Bs 3871 mcb and mccb in ac circuits

Switches for household and similar fixed electrical installations
Part 1: Specification for general requirements

1. BRITISH STANDARD 3871 : Part 1 : 1965
UDC 621.316.57
I SPECIFICATION FOR
MINIATURE
I
l AND MOULDED CASE
I CIRCUIT-BREAKERS
I
l Part 1. Miniature Abbreak
I
Circuit-breakers for amcm Circuits
BRITISH STANDARDS INSTITUTION
_____i
7
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2. SPECIFICATION FOR
MINIATURE
AND MOULDED CASE
CIRCUIT-BREAKERS
Part 1. Miniature Air-break
Circuit-breakers
for a.c. Circuits
B.S. 3871 : 1965
Incorporating amendments issued August 1968 (AMD 43),
November 1974 (AMD 1612) and May 1981 (AMD
3594)
BRITISH STANDARDS INSTITUTION
Incorporated by Royal Charter
2
PARK STREET, LONDON, W IA 2BS
Telex: 266933 Telephone: [phone]
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3. --
BSI BS*-3i71: PART81 b5 m Lb24bbî 0052754 5
B.S, 3871 : 1965
THIS BRITISH STANDARD, having been approved by the
Electrical Industry Standards Committee and endorsed by
the Chairman of the Engineering Divisional Council, was
published under the authority of the General Council
on
31st March, 1965.
The Institution desires to call attention to the fact that this
British Standard does not purport to include all the
necessary
provisions of a contract.
In order
to keep abreast of progress in the industries
concerned, British Standards are subject to periodical review,
Suggestions for improvements will
be recorded and in due
course brought to the notice of the committees charged with
the revision of the standards to which they refer.
A complete list of British Standards, numbiring over 9,000,
fully indexed and with a note of the contents of each, will be
found
in the BSI Catalogue which may be purchased from
BSI Sales Department, The Catalogue may be consulted in
many public libraries and similar institutions.
This standard makes reference to the foilowing British
Standards:
B.S.
7. Rubber-insulated cables and flexible cords for
electric power and lighting (for working voltages
up to and including i1 kV).
B.S.
842. Voltage-operated earth-leakage circuit-breakers
for use on consumers’ premises.
B.S. 2757. Classification of insulating materials for electrical
machinery and apparatus on the basis of thermal
stability in service.
B.S. 3042. Standard test finger (for checking protection
against electric shock).
1
British Standards are revised, when necessary, by the issue either
of amendment slips or of revised editions. It is important that
users
of British Standards should ascertain that they are in
possession
of the latest amendments or editions.
The following B.S.I. references relate to the work on tbis standard:
Committee reference
ELE/l0/23 Draft for comment AB(ELE) 11 18
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4. BSI BS*383L: PART*L b5 Lb24667 0052755 7
B.S. 3871 : 1965
CO-OPERATING ORGANIZATIONS
The Electrical Industry Standards Committee under whose
supervision this British Standard was prepared, consists of
representatives from the following Government departments
and scientific and industrial organizations:
Associated Offices’ Technical Cortunittee
*Association of Consulting Engineers
*Association
of Mining Electrical and Mechanical Engineers
*Association of Supervising Electrical Engineers
*British Electrical and Allied Manufacturers’ Association
*British Railways Board
*Cable Makers’ Association
*Crown Agents for Oversea Governments and Administrations
*Electrical Contractors’ Association (Incorporated)
‘Electrical Research Association
*Electricity Council, The Generating Board and the
Area Boards
in England and Wales
Electronic Engineering Association
*Engineering Equipment Users’ Association
Independent Cable Makers’ Association
*Institution of Electrical Engineers
*Ministry of Aviation
Ministry of Defence, Army Department
*Ministj of Defence, Navy Department
*Ministry of Labour (H.M. Factory Inspectorate)
*Minisfry of Power
*Minisfry of Public Building and Works
MunicipaL Passenger Transport Association (incorporated)
National Inspection Council for Electrical Installation Contracting
*National Physical Laboratory (D.S.LR.)
*Oil Companies Materials Association
*Post Office
*South
of Scotland Electricity Board
Electric Lamp Industry Council
Electric Light Fittings Association
Electrical Contractors’ Association of Scotland
Public Transport Association (Incorporated)
The Government departments and scientific and industrial
organizations marked with an asterisk
in the above list, together
with the following, were directly represented on the Committee
entrusted with the preparation
of this British Standard:
Association of Short-circuit Testing Authorities.
Engineer Surveyors’ Association
Lloyd’s Register of Shipping
London Transport Board
Ministry of Defence,
Air Force Department
National Coal Board
Radio and Electronic Component Manufacturers Federation
3
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5. BSI BS%3&7L: PART*L b5 = Lb2Llbbî 005275b 7
B,S. 3871 : 1965
CONTENTS
Co-operating organizations
Foreword
SPECWICATION
SECIION ONE : GENERAL
1. scope
2. Definitions
3. Service conditions
SECTION TWO : RATING, SIZES AND MARKING
4. Rating
5. Voltage and current ratings
6. Instantaneous tripping current
7, Short circuit capacities
8. Frequency
9. Circuit-breaker marking
10. Terminal markings
SECTION THREE : DESIGN AND CONSTRUCIIION
11, Temperature rise
12. Overcurrent device calibration
13. Time/current characteristics
14. Under-voltage release
15. Shunt-trip release coil
16. Construction
17. Operating mechanism
18. Connection arrangements
SECHON FOUR : TESTS
19. General
SECTION PIYE : TYPE TESTS
20. General requirements
21, Test duty sequence
4
Page
3
6
6
74
9
10
10
Il
Il
12
12
12
12
13
14
14
15
15
15
16
17
18
19
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6. BSI BS8387L: PART81 b5 = 1624669 0052757 0
Page
22. Selection of circuit-breakers 19
23. High-voltage test 19
24. Overcurrent device calibration test
25. Time/current characteristic test 20
26.
Temperature rise test 20
27. Overload performance test 20
28. Temperature rise check 21
29,
Endurance test sequence 21
30. Short-circuit capacity tests (general)
20
22
31. Short-circuit capacity tests (test duty sequence
and circuits)
23
32. Flexible cord test 25
34. Shock test 26
SECIION SIX : ROUTINE TESTS
35. High-voltage tests 27
36.
Performance tests 27
A.
B.
c.
D.
E.
F:
u.
M
APPENDICES
Application and selection of mhiature
circuit-breakers
28
Discrimination 31
Notes on terminology 32
Measurement of prospective current of test
Computation
of power factor from
Operation on short-circuit 33
duty circuit 33
oseiiiograms 34
hieasiuement of recovery voltage 35
Infurmatian to be included in records of
type i&$ for short-circuit capacity ratings 36
B.S. 3871 : 1965
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7. B.S. 3871 : 1965
BRITISH STANDARD SPECIFICATION FOR
MINIATURE AND MOULDED CASE
Part 1. Miniature Air-break Circuit-breakers
for a.c. Circuits
CIRCUIT-BREAKERS
FOREWORD
This British Standard has been prepared under the authority of the Electrical
industry 'Standards Committee and is the first part of a two-part standard
covering circuit-breakers of the miniature and moulded case
type. It is intended
to standardize a device which has become widely used
in industrial, commercial
and domestic electrical installations.
Part
2 of this standard, dealing with moulded case circuit-breakers, is in
course of preparation, Standards for current-operated earth-leakage circuit-
breakers and for miniature circuit-breaker distribution boards, are also being
prepared, and attention is drawn to
B.S. 842, ' Voltage-operated earth-leakage
circuit-breakers
'. It is common practice for a single unit to function both as a
miniature-breaker and
as an earth-leakage circuit-breaker.
Because of the difficulty in obtaining satisfactory and reproducible results,
it has not been found possible to specify in the present edition suitable tests for
mechanical strength, and resistance to moisture and heat.
Appendices have been included to assist in ensuring a proper application of
miniature circuit-breakers and attention
is directed to these, particularly to
Appendices
A and B.
SPECIFICATION
SECTION ONE : GENERAL
1. This British Standard specifies miniature a.c. air-break circuit-breakers (not
included in
B.S. 862) with -led cases for the mechanism and with fixed un-
adjustable time/ment characteristics. They are intended to be used for the
protection of industrial, commercial and domestic electrical installations. The
standard deals with circuit-breakers having voltage ratings up to
415 volts,
mnt ratings up to 100 amperes and short-circuit capacities up to 9ooo
amperes.
NOTE. It is racogniz,cd that miniature circait-breakers complying with this specification
may
bs UsSd on d.c. circuits. In such cases, the application of the circuit-breakers and the
relevancy of this standard should be the subject of agreement between the manufacturer and
purcimaor.
6
'
SCOPE
7
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8. ~
.~
BSI BS*3871: PARTS1 65 S 1b2Ltb67 0052757 4
B.S. 3871 : 1965
DEPïNiTiONS
2. For the pupposes of this British Standard the following deíìnitions apply:
u. Miniature circuit-breaker. @ereinafter referred to as circuit-breaker.) A
Compact mechanisril device for making and breaking a circuit both in normal
conditions, and in abnormal conditions such as those of overcurrent and short-
cira&.. In abnormal conditions the circuit is broken automatically.
b. Number ofpoles. The number of main conducting paths which the circuit-
breaker is required to open or close simuitaneously.
This includes a path normally intended for connection to a neutral conductor
but
does not include a switched neutral.
c. Switched neutral. Contach not intended to make or break current and
arranged to close before and open after the main contacts for the purpose of
isolating the neutral.
d. Case. The sealed container which encloses the circuit-breaker mechanism.
e. Enclosure. The container which encloses one or more circuit-breakers (for
the purposes of electrical distribution and/or mechanical
or climatic protection).
f. Prospective current. The current (r.m.s. value of the a.c. component) that
wodd flow
in a circuit due to the applied voltage if the circuit-breaker were
replad by a link or links of negligible impedance but without any other
circuit change.
NOTEI. For the purpose of this definition the tem circuit-breaker includes the short length
of cable used to connect the circuit-breaker to the test circuit.
g. Short-circuit capacity. The maximum value of prospective current at
which the circuit-breaker is capable of complying
with a prescribed test duty
cycle at the prescribed voltage and power factor
(see Clause 31).
h. Tripping factor. The ratio between the minimum value of overcurrent at
which the circuit-breaker
will trip and the current rating.
j. Main contacts. The ked and moving contacts in the main current carrying
circuit.
k. Arcing contacts. Contacts which open after, and dose before the main
contacts, to protect the latter from damage by an m.
I. Auxilhty contacts. Contacts working in conjwctlm with, and actuated
by the operation of, the main contacts, to control a cWt for opting auxiliary
devices such as trip coils or audible alarms.
m. Break. The sum of the gaps introduced in one poi@ between contacts or
arcing contacts (íï any) when the circuit-breaker is in the fdy opened position.
d
I I
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9. -___I_ ___
BSI BS*3871: PART81 b5 W Lb24bb9 005Z7b0 O W
B.S. 3871 : 1965
n. Overcurrent release. A device which causes the circuit-breaker to open the
circuit automatically when the current exceeds the predetermined value
at which
the release has been adjusted to operate.
p. Inverse time-lag overcurrent release. A device which retards the tripping
of the circuit-breaker by
a period of time which is an inverse function of the
overcurren
t.
q. Under-voltage release. A device which causes the circuit-breaker to open
the circuit
if the voltage falls below a pre-determined value.
r. Shunt-trip release. A device which enables the circuit-breaker to be operated
by
a relay, push-button or other apparatus which may be independent of the
circuit-breaker and arranged for distant operation.
s. Operating duty. A defined sequence of make and/or breaking operations,
carried out without any deliberate alteration to the main circuit in which the
circuit-breaker is placed.
t. Rating of a circuit-breaker. The set of values assigned by the manufacturer
to dehe the working conditions for which it is built.
u. Performance of a circuit-breaker, The general terms used to denote its
behaviour on, and the values obtained from, tests made on it in the prescribed
conditions.
v. Applied voltage, The r.m.s. value of the voltage applied to a test circuit
immediately before the initiation of current.
w. Recovery voltage. The normal-frequency r.m.s. voltage that exists across
the poles of the circuit-breaker immediately after ha1 arc extinction.
x. Rated voltage. The voltage assigned by the manufacturer to indicate the
nominal rams. system voltage between phases
or between phase and neutral for
which the circuit-breaker is intended.
y. Opening time. The time interval between the application of the test current
and the instant of contact separation.
NOTE. This is the equivalent of pre-arcing time for a fuse.
z. Total operating time, The sum of the opening time and the arcing time.
uu, Type test. A test intended to show that all circuit-breakers made to the
same specification and having the same essential details would pass an identical
test.
bb. Routine test. A test of every circuit-breaker made to the same specifìca-
tion.
I
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10. BSI BS*3873: PART81 65 Lb24bb7 00527bL 2
B.S. 3871 : 1965
cc. Instnntnneorts fuipping cityrent. The minimum value of current causing As bin): aiiiended 1981
the circuit-breaker to operate automatically with an opening time not
exceeding
O. 1 s.
Symbols. The follow&g symbols are used to deñne the steps of any
operating duty or test duty.
B-denoting a breaking operation;
M-denoting a making operation;
MMenoting a making operation, followed by a breaking Operation,
+(or a numera1)denoting a time in minutes between successive opera-
without the introduction of any intentional time lag.
tions
of an operating duty.
SERVICE CONDITIONS
3. Circuit-breakers complying with this standard shall be suitable for use in the
following conditions of service:
a. At an ambient temperature having a peak value not exceeding 35°C with
an average value not exceeding
30°C over any 24 hour period. .
The circuit-breakers are not suitable for exposure to d¡rect radiation from
the
sun or other source of heat likely to raise temperatures above the designed
ambient. Attention is drawn
to the possible effect on the tripping characteristics
due to variations in the ambient temperature
(see Clause 12).
NOTE. In normal conditions of service, the available cooling air is subject to natural atmo-
spheric variations
of temperature and hence the peak temperature occurs only occasionally
during the hot season and on those days when it does occur it does
not persist for lengthy
periods. Meteorological records indicate that temperatures
of at least 10 centigrade degrees
below the peak temperature
will occur within the 24 hour period, and that the average tem-
perature of any
24 hour period that includes the peak temperature will be at least 5 centigrade
degrees below the peak value.
b, At an altitude not exceeding loo0 m. above sea level.
c. In an atmosphere not subject to abnormally high humidity, excessive
pollution by smoke, chemical
fumes, salt-laden spray or other abnormal con-
ditions.
NOTE. Where service conditions differ appreciably from those specified above, the relevancy
of this standard should be the subject of agreement between manufacturer and purchaser.
9
As
altered
Nov.
1974
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11. - _____I_
BSI BSr387L: PARTrL b5 M Lb24bbî 00527b2 4
Voltage rating
B.S. 3871 : 1965
Nominal voltage to earth
SEKTION TWO : RATING; SIZES AND MARñING
RATING
’
4. Circuit-breakers shall be rated in terms ofthe following:
a. Number of poles.
b. Voltage.
c. Current.
d. Type, according to instantaneous tripping current.
e. Short-circuit capacity.
f: Frequency.
,ismiem/?(/
iIlfl): 1981
240
415
VOLTAGE AND CURRENT RATINGS
240
240
,luniiieii</ec/ 5. a. The voltage ratings are not standardized, but preferred values are given in
Table
IA.
May. I98 I
TABLE lA, VOLTAGE RATINGS
b. The current ratings are not standardized, but preferred values are given in
Table
1B.
TABLE 1B. CURRENT RATINGS
Amp
5
6
10
15
16
20
25
30
32
Amp
40
45
50
60
63
1 O0
10
i-
,___-.
:,
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12. BSI BSX3BïL: PART*& b5 E Lb24bb9 00527b3 b W
I--
loo0
1500
2000
3000
4000
6000
B.S. 3871 : 1965
0.85 to 0.9
0.8 to 0.85
0-75 to 0.8
04'5 to 0.8
0.75 to 6.8
0.75 to 0.8
INSTANTANEOUS TRIPPING CURRENT
M9
6. Circuit-breakers are classified according to their instantaneous tripping
current as given in Table
2.
~xaimw/e[/
May, 1981
I TABLE 2. TYPES OF CIRCUIT-BREAKER, ACCORDING i
TO INSTANTANEOUS TRIPPING CURRENT
9000 0.55 to 0.6
instantaneous tripping current
Amp
> 2.7 I,,,< 4.01,
> 4.01n,< 7.01,
> 10 In,<50 I,
> 7.01n,< 10 In
> 3 In,< 5 In
> 5 In,<10 I,
>10 I,'<20 In
SHORT-CIRCUIT CAPACTlIES
7. Category of duty. Circuit-breakers are rated according to their category of
duty. The categories are not standardized, but preferred values are given in
Table
3.
Asariierided
May, I981
TABLE 3. CATEGORIES OF DUTY
I- l
M1
M1.5
M2
M3
M4
M6
The code for the category of duty consists of the short-circuit capacity
expressed in kiloamperes preceded by the letter
'M'. For categories of duties
other than the preferred ones given in the table, the range of power factors of
the test circuit shall be taken to be the same as that for the next higher category
of duty in the table, e.g. for the non-preferred category of duty
M8, the power
factor ofthe test circuit shall be
0.55 to 0.6, i.e. the same as for category ofduty
M9.
Asarrieiided
b*ay~19s'
-
11 - -.
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13. BSI BS*387L: PART*L 65 LbZLlb69 U05Z7bLl 8
B,S. 3871 : 1965
8. Frequencies are not standardized. The preferred value is 50 Hz and this
PREQUENCY
nsniiieiic/ed
híny. i981
value shall be assumed unless otherwise specified.
As nrrteiided
hifly, i981
Al
allered
Nov.
1974
NOTE. In general, circuit-breakers rated for 50 Hz are suitable also for 60 Hz.
CIRCUIT-BREAKER MARñING
9. Circuit-breakers shall be indelibly marked with the following particulars:
a. B.S. 3871.
b. Rated voltage and the associated number of phases.
c. Rated current.
d. Reference calibration temperature.
e. Type, according to instantaneous tripping current.
J: Manufacturer's name or distinguishing mark,
g. Frequency, if other than 50 Hz.
h. Manufacturer's type reference, where more than one type is
j. Category of duty.
k. Country of manufacture.
manufactured.
NOTE. The current rating should be readily visible without removing the circuit-breaker
from
its mounting.
TERMiNAL IMARIUNGS
10. The terminals shall be clearly and indelibly marked for those circuit-breakers
which require distinction between the supply side and the load side and/or
between phases and neutral,
SECXION THREE : DESIGN AND CONSTRUCi'ïON
TEMPERATUREBISE
11, The temperature rise, measured by any suitable method, shall not exceed
the values given below when the circuit-breaker is tested in accordance with
Ciause 26.
a. Terminals (for connection of external conductors) of
circuit-breakers fitted with copper contacts.
b, Terminals (for connection of external conductors) of
circuit breakers fitted with contacts having adequate and
durable facings
of silver or materials not subject to
progressive deterioration.
50 degC
35 degC
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14. ~
BSI BS%387L: PART*l b5 9 lb24bb7 0052765 T W
Inealptfng materiai
B.S. 3871 : 1965
Maximurn temperatme rise
Class Y
Class A
class E
class B
Class F
class H
55
70
85
95
120
145
~~ ~
NOTE. Details of insulatins materials covered by the classes specified in Table 4, arc con-
tained in B.S. 2757, ‘Classification of insulating materiais for electrical machineqr and
apparatus on the basis of thermal stabiiity in service ’.
OVERCURBENT DEVICE CALIBRATION
12. a. The circuit-breaker shall have a fixed unadjustable time/current As a»ieaúeú
May, 1981
tripping characteristic.
b. The calibration shall be such that the circuit-breakers, according to their
type and rating, comply with the requirements
of Table 5 when tested in the
conditions specified in Clause
24.
13
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15. ._--
c_--
B.S. 3871 : 1965
---
1
5Pe of
. instantaneous
opera tion
1234
1234
1234
it 2j 3t 4t
1
li
2
2t
3
3t 4
4
1234
1234
1234
BCD
BCD
B C D$
B
C D$
BCD
BCD
B C D$
B C DS
BCD
BCD
Bt Ct Dt
Bt C$ Dt
Bi Cj Di
B
4t
C
Bt
D
c;
Di
Rated
current,
In
Amp
AU ratings
6 10
> 10
All ratings
AU ratings
AU ratings
Ali ratings
AU ratings
Ali ratings
AU ratings
AU ratings
Ali ratings
Ali ratings
6 10
> 10
Ali ratings
< 63
> 63
< 63
> 63
< 63
> 63
< 63
> 63
< 63
> 63
All ratings
< 32
> 32
AU ratinss
AU ratings
AU ratings
AU ratings
AU ratings
All ratings
Test
current
Amp
1.0
I,
l.s In
1.35 In
2.5 In
2.7 I,
4.0 I,
4.0 In
7.0 I,
7.0 I,
10 I,
6.0 I,
10 I,
50 I,
1.75 In
1.5 I,
0.9 In
1.131,
1.131,
1.45
I,
1.45 In
1.13 In
1.13 I,
1.9 In
1.9 I,
In
In
2.55
In
2.55 In
2.55 I,
3 In
5 In
5 In
10 I,
10 I,
20 I,
TABLE 5. OPERATING DUTIES
Test
period
2h
lh
Ih
is-60s
0.1
s
0.1 s
0.1 s
0.1 s
0.1 s
0.1 s
10 s
0.i s
0.1 s
lh
lh
2h
lh
2h
lh
2h
lh
2h
lh
2h
lh
2h
1s
1
min
2 min
0.1 s
0.1 s
0.1 s
0.1 s
0.1 s
0.1 s
Result
No trip
Trip
Trip
Trip
No trip
Trip
No trip
Trip
No trip
Trip
Trip
No trip
Trip
Trip
Trip
No trip
No trip
No trip
Trip
Trip
No trip
No trip
Trip
Trip
No trip
No trip
No trip
Trip
Trip
No trip
Trip
No trip
Trip
NO trip
Trip
Ambient temperature
Reference
calibration
te21
20
Alin.
OC
20
20
20
20
20
20
20
20
20
20
20
20
20
O
O
34
-
-
iture
-
Max.
OC
25
25
25
25
2s
25
2s
25
2s
25
25
25
25
5
5
36
-
-
Min.
OC
-
30
30
30
30
-7
-7
-7
-7
38
38
30
30
30
30
30
30
30
30
30
40
40
40
40
20
54
35
35
35
35
-3
-3
-3
-3
42
42
35
35
35
35
35
35
35
35
35
1
*The reference calibration temperature for types B, C or D shall be 30 'C and for types 1,2,3 and 4 shall be either
20
'Cor 40 OC, lhe purpose of the latter value being to avoid the necessity of de-rating thermaiiy sensitive circuit-
breakers which are
IO be mounted in enclosures.
+These tests are repeated in Table
8.
$See Clause 24.
-
Mas.
OC
45
45
45
45
45
45
45
45
45
45
45
.
45
45
25
25
56
-
-
_-
g_- ~-
It shall be possible to reclose a circuit-breaker on to rated current within
c. All circuit-breakers rated at Fa@ or less shall be checked in accordance,
14
five minutes of the end of the minimum trip test.
with Clause
32 for their ability to protect sinal1 flexible cords.'
-
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16. -
BSI BSg3871: PARTg1 65 = 1624669 0052767 3 =
TiME/CURRENT CHARA<;TERIsTIcS
13. Time/current characteristic curves shall be prepared in accordance with
Ciause 25 and the manufacturer shall make copies available to the purchaser
upon request.
NOTE. It is recommended that the time scale be plotted vertically and the current scale
horizontally.
14. If an under-voltage release is provided it shall operate on a slowly faiüng
voltage, at normal frequency, between the
limits of 66 per cent and 10 per cent
of the normal operating voltage.
Ar uiiieiided
Alu& I981
The curves shall be prepared with both axes scaled logarithmically.
UNDER-VOLTAGE RELEASE
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17. . BSI BS*387E: PART*I b5 m Lb2Ltbb9 0052768 5
B.S. 3871 : 1965
Ab half the normal frequency, the lower limit of operation shall be not less
If the release is self resetting it shall require not more than 85 per cent of
than
15 per cent of the normal operating voltage.
the normal operating voltage to reset it.
15. If voltage operated tripping coils are provided they shall operate betwe&
the
limits of 60 per cent and 110 per cent of the normal operating voltage.
16. The operating mechanism case shall be effectively sealed by the manufactura
to prevent access to the mechanism.
The case may be of insulating material or
of metal, and shall be designed to withstand reasonably rough usage without
fracture or permanent distortion.
The construction shall be such that when the circuit-breaker is mounted as
in service, any person operating the circuit-breaker shall be safeguarded from
injury.
Live parts shall not be accessible to the standard test fìnger specified in
B.S. 3042.
Provision shall be made for earthing of exposed metal parts which require
earthing in accordance with the current edition of the ' Regulations for the
elecjrical equipment of buildings
', published by the Institution of Electrical
En&ineers. If an earthing teminal is provided it shall have a size of not less than
M5 if of steel, or M6 if non-ferrous metal,
Metallic contact with the enclosure, if of metal, is deemed sufficient earthing
for movable parts such
as covers. When the earthiiig termina! is of steel, it shall
be effectively protected against corrosion.
NOTE. Manufacturers should provide, if required, means for ensuring that circuit-breakers
cannot inadvertently
be switched to the ON position. Such means can, for example, be pro-
vided by the use of circuit-breakers
of the withdrawable type.
S"T-"RIP RELEASE COIL
CONSTRUCïíON
OPERATìNG MECHANISM
17, Circuit-breakers shall be arranged for manual closing and opening and for
The mechanism shall be fitted with an automatic release which shall at all
times function independently
of the means used to close the circuit-breaker.
Both the
ON and OFF position of the circuit-breaker shall be clearly indicated.
The indication shall
be clearly visible to the operator when the circuit-breaker
is mounted in the normal manner.
The metallic portions of the mechanisms shall be either iiiherently resistant
to, or
so treated as to make them resistant to, atmospheric corrosion.
automatic tripping
on overcurrent. As altered
1968
15
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18. B.S. 3871 : 1965
CONNECïION ARRANGEMENTS
18. If wiring terminals are provided, they shall adequately accommodate and
securely clamp the conductors specified in Table
6.
addition, have adequate means for accommodating and clamping firmly any
number
of conductors each size 2.5 mm2, up to and including three.
~ísom~ided Each terminal of circuit-breakers having a rating of 30/33 amp 'shall, in'
Alop. 1981
i
AS anieiided
híay, 1981
TABLE 6. TERMINAL CAPACITIES
35
Circuit-breaker
rating
A
5fG
20
30132
50
- --. 1
GOT67
To accommodate and clamp conductors of
1 and 2-pole
mm2
2.5 (2 cables)
4
10
16
16
'>C
3 and &pole
mm2
2.5 (2 cables)
4
10
16
25
I
16
I
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19. BSI BS%387-I,: PART*I, b5 m Lh2qbb9 0052770 3 m
B.S. 3871 : 1965
SECTION POUR : TESTS
GENERAL
19. Tests shall be made to prove compliance with all the requirements of this
standard. It is not intended, nor is it recommended, that every circuit-breaker
shali be subjected to all the tests.
Two
kinds of tests shaü therefore be recognized namely, type tests which
shali be made on
a representative sample or samples of each type of apparatus,
and routine tests which shaii be made on each individual piece of apparatus
manufactured
to this standard.
17
./------
------i
-7
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20. A
BSI BS*3871: PART*3 b5 = 162qbb9 0052773 5
B.S. 3871 : 1965
SECIION FIVE : TYPE T.WTS
As
altered.
Nov.
1974
As attittided
Mny. 1981
GENERAZ. REQUIREMENTS
20. If specified when inviting tenders, certificates giving records of type tests on
a circuit-breaker identical in all respects with the one being purchased shall be
furnished by the manufacturers.
Certificates of all type tests, with certified detailed drawings of the type of
circuit-breaker, shall
be held available by the manufacturer, together with a
record of any alterations, whether essential
or not, which have been made to
the circuit-breaker since the test.
Type tests may be made by the manufacturer provided that he shall arrange
for a recognized authority to make any type test for which he himself is not
equipped.
Unless otherwise specified, tests shall be made at a frequency
of 50 Hz rt 10
per cent and at an ambient of between 20°C and 25°C.
Unless otherwise specified in the relevant test clauses, the circuit breaker
shall be mounted individually, vertically and
in free air and shall be protected
against undue heating
or cooling. It shall be wired with the cables specified in
Table
7 and shall be fixed to a metal support, the method of fixing complying
with any requirements relating
to the means of mounting recommended by the
manu fact urer.
--__
_I_ - - - -
TABLE?. CABLE SIZES FOR TÈSTS
Circuit-breakel
current rating
A
516
10
15/16
20
25
30132
40
45 .
As attietided 50
hfaJI, 1981 60163
1 O0
Cable size
One- and two-pole
circuit-breakers
rnm'
1
1.5
2.5
2.5
4
6
10
10
16
16
35
Three- and four-pole .
circuit-breakers
inni2
I
1.5
2.5
4
4
6
10
10
16
25
3s
.
'The length of cable used to connect the circuit-breaker to the test circuit ;
shall not exceed a total of 1.2 f 0.05 m per pole.
For circuit-breaker ratings not specified in Table
7 the cable size for the
next higher
rating shall be used.
,
18
~ _--- -- f==---i
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21. B.S. 3871 : 1965
TEST DUTY SEQUENCE
21. u. The following type tests shall be made on circuit-breakers as specified in
Clause 22. The circuit-breaker samples shall be in a clean new condition at .the
commeucement of each test-duty sequence, and the specified sequence shall
be
completed without any adjustment being made to the samples.
Samples shall
be submitted to the following test-duty sequence:
High-voltage test Clause
23
Overcurrent device calibration test Clause 24
Temperature rise test Clause 26
Overload performance test Clause 27
Temperature rise check Clause 28
Endurance test
Calibration check Subclause
29c
Fresh samples shall be submitted to the following test-duty sequence:
Rating check Subclause~JOa
Short-circuit capacity tests
Insulation resistance test Subclause
30j
Calibration check Subclause 30k
Subclauses 29a and b
Subclauses 306 to h
I The time/current characteristic test (Clause 25), flexible cord test (Clause
As
32), and shock test (Clause 34) are separate tests. For each of these tests
Nov. u"ered
additional &cuit-breakers in a clean new condition shall be used.
1974
SELECXION OP CIRCUIT-BREAKERS
22. Circuit-breakers shall be submitted to the test-duty sequence as follows: A F ainerideri
Muy. i981
a. One each of the highest and lowest preferred current ratings (see
Table
1B) to the test-duty sequence specified in Subclause 2 Ib.
b. Samples of the highest and lowest preferred current ratings (see Table 1B)
within each category of duty assigned to the circuit-breaker (see Table 3) to the
test-duty sequence specified in Subclause
2 IC.
HIGH-VOLTAGE TEST
23. For this test the circuit-breaker shall be in a clean new condition.
be applied for one minute between the following parts:
closed.
circuit-breaker closed.
terminal with the circuihbreaker open.
Circuit-breakers shall withstand a test voltage of
2ooo volts r.m.s. which shall
(i) Between all individual incoming terminals with the circuit-breaker
(ii) Between all incoming terminals and the earth terminal (if fitted) with the
(iii) Between each incoming terminal and the corresponding outgoing
19
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22. ~ ~~~~~ ~ ~~
BSI BSX387.L: PART*& 65 E Lb246b9 0052773 9 E
B.S. 3871 : 1965
(iv) Between terminals and any other metal parts unearthed and exposed in
The tsst voltage shall be alternating and of any convenient frequency be
service.
tween
25 and 100 Hz and approximately of sine wave form.
OVERCURRENT DEVICE CALIBRATION TEST

24. Compliance with the requirements of Subclause 126 shall be checked by
operating the circuit-breaker between the specified limits of ambient temperature,
at any convenient test voltage and power factor, at the relevant current values.
Opening tiines shall be measured starting from the specitied ambient tem-
rature in each
case; except for the tests at 1.45 In or 1.9 í,, on types B, C
and D which shalTfollow the tests ax13 1, at the sanie ambient temperature
Multi-pole circuit-breakers shall
be tested on all poles simultaneously and
also
on each pole separately. When testing single poles of multi-pole circuit-
breakers, the values of the test current may
be increased by 20 per ?nt except
for
No-trip tests. ..
__~ ~ - - __- - -.
I Q yithin I 5 sew - - - ~
II
TIME/CURRENT CHARACXERISTIC TEST

25. Time/current characteristics of circuit-breakers shall be ascertained by
causing them to operate at not less than six different currents so chosen as to
.The lowest
of the currents shall be not greater fhan 1 .O5 times the 1
the highest of the currents shall cause the circuit-breakers to trip in not more
than 0.1
s., _-
'
Points corresponding to total operating times at higher currents obtained
from the test specified in Clauses 30 and 31 shall be plotted
on the same graph,
and the curve shall
be extended in accordance with the indication of these points.
1. ,
facilitate the production of a curve of the kind shown in Fig. 8. 2-
t
,'&iinum tripping current of the circuit-breakers as specified in Table 5 and
--z- -- --
-a
~ -- =-
- -
TEMPERATURE RISE TEST
26. The rated current shall be passed until the circuit-breaker attains a steady
temperature.
For the purposes of this test sready is defined as not changing by ,r
more than one centigrade degree in 30 minutes.
Alternating current shall
be used for this test.
OVERLOAD PERFORMANCE TEST
27. The circuit-breaker shall be submitted to 35 maksbreak operations, closing
and opening manually if possible, and 15 make-brak operations, closing manu-
ally and opening automatically, at a rate of
4 make-break operations per minute,
NOTE. If the circuit-breaker does not latch in at the specified rate of operation the rate
should
be reduced sufficiently so that the circuit-breaker will just stay in.
20
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23. BSI BSm3871: PART*& 65 3b24bb9 0052774 O W
B.S. 3871 : 1965
The value of the current shall be equal to 600 per cent of the rated current
of the circuit-breaker with a minimum of
150 amperes.
The test shail be made at
100 f 5 per cent of rated voltage and at a lagging
power factor of
0.7 to 0.8.
The current in the test circuit-breaker shall be limited to the required value
at the
spec^^ power factor by means of reactors and/or resistors COMected
on the load side of the test circuit-breaker.
The impdance of the supply circuit shall
be such that the voltage regulation
will not excd 15 per cent except that the impedanse of the supply circuit may
be increased
so that the short-circuit capacity at the line terminals of the circuit-
breaker does not exceed the rated short-circuit capacity of the circuit-breaker.
Resistors and inductors shall not be connected
in parallel except that:
Resistors shall be connected between phases or between phase and neutral,
after the impedances for adjusting the prospective current,
so as to draw a
current of 10 amperes per phase from the supply:
If an air-core inductor is used, a resistor taking approximately one per
cent
of the current through the inductor shail be connected in parallel with it.
TEMPERATURE RISE CHECK
28. At the conclusion of the test specified in Clause 27 the circuit-breaker shall
successfuüy pass a temperature rise check made in accordance with the conditions
of test specified
in Clause 26.
The circuit-breaker shall be deemed to have failed the test if it trips auto-
matically during the test
or if the temperature rise at the terminals, in the steady
state, excd by more than
10 degC the temperature rise permitted in the clean
new condition
(see Clause 11).
ENDURANCE TEST SEQUENCE
29. a. On-load endurance test. Circuit-breakers shall be operated by manual or
equivalent
means ON and OFF 6ooo times at a rate of 240 &- 30 times per hour,
each oN/oFF cycle being approximately 2 seconds ON and 13 seconds OFF.
During the test each pole of the circuit-breaker shall carry its full rated
current at
100 f 5 per cent of rated voltage and at a lagging power factor of
0.7 to 0.8, the test circuit being -ranged as specified in Clause 27.
6. O$-Ioad endurance resr. Circuit-breakers shall then be operated by manual
or equivalent means ON and OFF 4ooo times at the rate specified in Subclause a
above.
c. Calibration check. At the conclusion of the off-löad endurance test the
opening time, at a current value
of twice the rated current and at the reference
calibration temperature shall be measured,
Asarnertded
‘”’
21
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24. BSI BS*3875i: PART*L b5 m Lb24669 0052775 2 m
B,S. 3871 : 1965
A
The opening time shall not exceed three minutes.
NOTE. Where circuit-breakers are fitted with optional extra features such as shunt trip
coils, auxiliary contacts, etc., the relevancy of this Clause should be the subject of agreement
between manufacturer and purchaser.
-- 30. -- & -__ For circuit-bieakers, __ types 1, 2-3-and 4, sadubmitted for this te&
shall have bEiiteped to check that they will not tripswithin two hours when
~~JI-Y&I~ rated cuqent; and that tfie opening the at-1.5 times rated curr.ent,
fQKsircg~~reakers rated up to
and includine 1[1 ZWIID. a nd 1. 5 times rated!
-_ current, for circuit-breakers rat- above ~ 10 ~p,~~mplies withF-a
SHORT-CIRCUIT CAPACITY TESTS (GENERAL) A’-
--~ --
.
-
cpecifiedh SugdaGër26717 __
~ --_b__--
For circuit-breakers, types B, C and D, saiiiples subinitted for this test shall
have been tested to check that when
a current of 1.13 I,, is passed through all
poles for the time specified
in Table 5, the’circuit-breaker does not trip and
when the current is then increased within
5 s to 1.45 I,, the circuit-breaker
.
,sco,ic,,i~(ed
.\In?: 1981 - - --
As
altered
No v.
1974
shall trip within ___ the - time specified in Table 5;
b. The metal support on which the circuit-breaker is mounted, together with
all metal parts normally earthed in service, shall
be connected to the neutral
through
a tine wire fuse having a minimum length ot‘75 mm. The fuse shall be,
a tinned coppcr wire not greater
than 0.125 mm diameter and shall remain
intact at the conclusion of the complete series
of tests.
c. During all breaking capacity tests cheesecloth shall be applied to the
exterior of the circuit-breaker
as indicated below.
The cheesecloth shall be clean and
dry, bleached, plain cotton, approximately
30-40 grams per square metre. When placed in position the cheesecloth shall
be folded loosely in such a manner that cut’or tom edges will not be exposed
directly
to the arc or flash.
There shall
be no ignition of the cheesecloth. The material may be changed
during the series of tests.
(i) For circuit-breakers intended to
be used in an enclosure, cheesecloth
shall be placed on the outside of the enclosure at all openings, handles, etc.,
and inside the enclosure wherever
insulated conductors may be located, care
being taken not to block the vents.
(ii) For circuit-breakers not intended to
be used in an enclosure, cheese-
cloth shall
be placed at all openings, handles, etc., care being taken not to
block the vents.
(iii) Circuit-breakers
so constructed that they may or may not be fitted
in an enclosure shall be tested as in (i¡) above.
d. Ail poles of multi-pole circuit-breakers shall be tested simultaneously, the
test circuit being arranged
io represent a normal condition under balanced
loading. In addition, tests shall
be made on individual poles of multi-pole
circuit-breakers in accordance with Subclause
31g.
more than 110 per cent of the rated voltage. The recovery voltage shali be not
less than 95 per cent nor more than 105 per cent of the rated voltage and shall
I
e. The applied voltage shall be not less than 100 per cent and shall be not I ..
-
22
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25. BSI BS*38?2: PART*l b5 L624669 0052776 4 rn
B.S. 3871 : 1965
be raaintained for at least 30 seconds after the interruption of the short-circuit
current-m the final
MB operation in a sequence?
f. Impedances used for linriiting the prospective short-circuit fault current to
the
quirai values shall be inserted on the supply side of the circuit-breaker
under test. (See Fig. 1 to 6.)
Resistors and inductors shall not be connected in paraliel, except that:
(i) Rexiston shall
be connected between phases or between phase and
neutral, after the impedances for adjusting the prospective current, so as to
draw
a current of 10 A per phase from the supply.
(5) If an air-core inductor is used, a resistor taking approximately one
per cent of the current through the inductor shall be connected in parallel
with it.
g. Tests shall be made in accordance with Clause 31, on each sample at
both 30 per cent and 100 per cent of the rated breaking capacity at the power
factor specified in Table
3.
The time interval between successive operations at each value of test current
shall
be 2 minutes or the inherent resetting time of the circuit-breaker whichever
is the greater.
h. All circuit-breakers shall successfully perform the appropriate sequence of
break and make-break operations specified in Clause 3 1. Circuit-breakers
intended for use in
a 240 volt single phase system shall be tested in accordance
with Clause
31a or 31b. Single-pore circuit-breakers intended for use in a
415 volt three phase system shall be tested in accordance with Clause 3 IC.
j. The insulation resistance shall be measured within 3 minutes of the con-
clusion of the series of tests. The test shall
be made at 500 volts d.c. and the
resistance shall
be not less than:
(i)
A quarter megohm between all individual incoming terminals with the
circuit-breaker closed,
(ii)
A half megohm between ali incoming terminals and earth with the
circuit-breaker closed.
(iii)
A quarter megohm between each incoming terminal and the cor-
responding outgoing terminal
wtih the circuit-breaker open.
(iv)
A half meghom between terminals and any other metal parts un-
earthed and exposed in service.
k. The opening time at twice rated current, at the reference calibration
temperature, shall then
be measured,
The opening time shail not exceed three minutes.
31. The short-circuit test duty sequence at each value of the test current and the
method of connection of the circuit-breakers and the testing apparatus shall
be
appropriate to the rating of the circuit-breaker as follows:
23
ASOIIICII(M
"'w "'"
r~SOJIld~led
May, I581
.
SHORT-CIRCUïï CAPACITY TS.
fleit duty wuence and circuits) -
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26. B.S. 3871 : 1965
,is nirieti(icii a. Single-pole circuit-breakers of 240 volt single phase rating. For this test
three circuit-breakers shall be used and the test circuit shall be
as shown in
Fig.
1, The following tests shall be made:
(i) One break test
on the three circuit-breakers simultaneously.
(ii)
A test duty MB-2-MB on each of the three circuit-breakers
b. Alternative method of testing single-pole circuit-breakers of 240 volt
single phase rating.
For this test three circuit-breakers shall be tested and the
test circuit
shall be as shown in Fig, 2. The following tests shall be made:
a test duty: B-2-MB-2-MB on each circuit-breaker.
’ *\lm I Y81
independently.
As nrtietidcù
May, I981
Pointsn-wave switching shall be used for the break test to ensure that the
points
of initiation of the short-circuit on the three samples are spad at
approximately
60 electrical degrees from each other.
c. Singie-poie circuit-breakers of 415 volts, 3-phase rating. For this test
three circuit-breakers shall be used and the test circuit shall be as shown in
Fig. 3, The following tests shall be made:
(i) One break test
on the three circuit-breakers simultaneously.
(ii) With the circuit-breaker (a) closed and circuit-breaker (b) open an
MB test shall be made on circuit-breaker (c).
(iii) With the circuit-breaker (b) closed and circuit-breaker (c) open an
MB test shall be made on circuit-breaker (a).
(iv) With the circuit-breaker (E) closed and circuit-breaker (a) open an
ME test shall be made on circuit-breaker (b).
During these tests any or all of the circuit-breakers under test may operate
to clear the fault; and every circuit-brbaker shall trip automatically at least once.
if they do not, the entire sequence of tests shall be repeated once more with three
fmh samples.
d. Double-poie circuit-breakers. For this test, threa circuit-breakers shall be
used and the test circuit shall be as shown in Fig. 4. The line-to-neutral voltage
shall be
in accordance with the voltage rating of the circuit-breakers,
The following tests shall be made:
(i) One break test, the three circuit-breakers being tested simultaneously.
(ii) A test duty MB-2-MB on each of the three circuit-breakers inde-
e. Alternative test for double-pole circuit-breakers. For this test thea circuit-
breakers shall
be tested and the test circuit shall be as shown in Fig. 5. The
following tests shali be made:
pendently.
A test duty E-Z-MB-2-ME on each circuit-breaker.
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27. s BSI BSa387L: PARTrL 65 Lb2Llb69 0052778 8
B.S. 3871 : 1965
Point-on-wave switching shall be used for the break test to ensure that the
points
of initiation of the short-cifcuit on the three samples are spaced at approxi-
mately
60 electrical degrees from each other.
f. Triple-pole and triple-pole and neutral circuit-breakers. For this test a single
circuit-breaker shall
be tested and the circuit shall be as in Fig, 6. The following
tests shall
be made:
B-2-MB-2-MB.
g. Individual poles of multì-pole circuit-breakers. In the case of multi-pole
circuit-breakers an additional sample shall also
be tested. Each pole of this
sample shall
be subjected individually to the following test sequence made at
100 per cent of rated breaking capacity only.
B-2-MB-2-MB.
For the purpose of this test the applied voltage shall be the rated line-to-
neutral voltage. At the conclusion of the test the circuit-breaker shall
be capable
of making and breaking its rated current at rated voltage.
FLEXIBLE CORD TEST
(For circuit-breakers UP to and includhg 6 amp only)
32. For this test the circuit-breaker shall be in a clean new condition. As
altered
Nov.
1974
Each pole of a multi-pole ckcuit-breaker shall be tested separately.
A
A
A
The test circuit shall comply with the requirements of Subclauses 30e and&
240 V beiig regarded as the maximum rated voltage.
BS 6500.: 1984\, a single core length of not more than 100 mm shall be taken
and connected in the test circuit as shown in Fig.
7. T& connections shall be
completed by means of
1.5 mm2 cable to 'BS 6004 : 1984, not less than 4.5 m
nor more than
5 m in total length.
The circuit-breaker shall successfully withstand a
break operation followed
by two successive make-break operations with a prospective breaking current of
loo0 amp at a power factor of 0.8 to 0.9 lagging, at incoming terminals ' X'
and ' Y ' (see Fig. 7). Thecooling interval between operations shall be 10 seconds
or the inherent resetting time of the circuit-breaker, whichever is the greater.
"he circuit-breaker shaii not fail to interrupt the circuit, and the flexible cord
shall
be in good usable condition after the series of operations.
33. Tungsten filament-lamps test.
(This clause deleted in accordance with
AMD 1612).
~
-.
From the length of twin core 0.5 mm2 flexible cord complying withTable 15,
25
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28. BSI BS*3871i: PARTS1 65 D Zb24bb9 O052779 T D
B.S. 3871 : 1965
I
SHOCK TEST
34. For this test, the circuit-brkker shall be in a clean new condition and shall
be fixed to the test apparatus shown in Fig. 14.
Prior to the commencement of the test, the circuit-breaker shaii carry 0.7
times its rated current for one hour.
The test shall
be made with the circuit-breaker closed, and carrying 0.7 times
its rated current, the supply
being at any convenient voltage. A multi-pole
circuit-breaker shall
carry 0.7 times its rated current on all poles.
The apparatus platform shall
be lifted at its free end and then aiiowed to fali
from a .height
of 3 mm 50 times, with an interval of one second between each
fall.
The circuit-breaker shall not open throughout this test.
The test shaii be made in three directions, along the three axes of the circuit-
breaker.
As
dtered
Nov.
1974
.. .
-----
I-.
I
26
..
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29. BSI BS*387&: PART*& 65 9 Lb2LIbbî 0052780 b
B.S. 3871 : 1965
SECTION SM : ROUTINE TESTS
HIGH-VOLTAGE TEST
35. For this test the circuit-breaker shall be in a clean new condition.
shall
be applied momentarily between the following parts:
Circuit-breakers shall withstand a test voltage of
2000 volts r.m.s. which
(i) between all individual incoming terminals with the circuit-breaker
(ii) between all incoming terminals and earth with the circuit-breaker
(iii) between
each incoming terminal and the corresponding out-going
(iv) between terminals and
any other metal parts unearthed and exposed
The test voltage shall be alternating and of any available frequency between
closed.
closed.
terminal with the circuit-breaker open.
in service.
As
E:d
1974
25 and 100 Hz and approximately of sine wave form.
PERFORMANCE TESTS
36. To ensure that the circuit-breaker complies with the requirements of
Clause 12, it
is sufficient for each circuit-breaker to be tested to ensure that it
trips within the time specified in Table
8. Where appropriate, tests shall also be
made to ensure that the circuit-breaker complies with the requirements of
Clauses 14 and
15.
TABLE 8. OPERATING DUTIES FOR ROL
; Typeof
instantaneous
operation
1234
1
2
3
4
BCD
' BCD
. BCD
B
I
C
D
Rated
current,
In
hP
All ratings
All ratings
All ratings
All ratings
All ratings
Ail ratings
<32
A
>32 A
All ratings
All ratings
All ratings
Test
current
hP
< 2.5 I,,
4.0 In
7.0 In
10 I,
50 I,
2.55 In
2.55 In
2.55 r,
5 In
10 In
20 I,
INE TESTS
~
Test
period
ls-6Os*
0.1 s
0.1 s
0.1 s
0.1 s
1 s*
1 min*
2 min*
0.1 s
0.1 s .
0.1 s .
Result
Trip
Trip
Trip
Trip
Trip
No trip
Trip
.
Trip
Trip
Trip
Trip
~-
*These values can be amended to ensufe that the requirements of Table 5
are met for breakers when tested at their reference calibration temperature.
Table
5.
NOTE. The values in this Tableare extracted from the values given in -
L
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. BSI BS*387&: PART*& b5 W Lb24bb9 0052783 B W
B.S. 3871 : 1965
APPENDIX A
APPLICATION AND SELECTION OF MINIATURE
CIRCUIT-BREAKERS
Miniature circuit-breakers are designed to provide a convenient means of pro-
tecting circuits against the effects of overcurrents and short-circuits; at the same
time they permit ready restoration of the supply without any servicing.
This standard incorporates a series of making and breaking capacity tests
designed
to ensure that the circuit-breaker is capable of clearing a number of
short-circuit faults at its full rated breaking capacity, whilst still remaining in a
good serviceable condition.
The most important technical. factors, upon which the correct selection of
circuit-breakers for any installation depends, are set out below. The headings
indicate the kind of information which should
be supplied by the purchaser
with enquiries or orders.
Al, System voltage, The voltage rating of the circuit-breakers in a circuit
should
be not less than the r.m,s. a.c. voltage between conductors of that circuit.
The nominal voltage between conductors and earth should not exceed
250 volts.
A2. Number of poles. Miniature circuit-breakers are suitable for use on single-
phase
or polyphase supplies. The more common applications for the various
types are given below.
Single phase supply
a, Single-pole circuit-breaker, A circuit-breaker having one pole which is
fitted with an overcurrent release. It is intended for connection in the phase
conductor of
a single-phase and neutral supply.
6. Single-pole and solid-neutral circuit-breaker, A circuit-breaker having one
pole which
is fitted with an overcurrent release for connection in the phase
conductor and also, a solid conducting path with terminations to allow connec-
tion of the neutral conductor of a sizgle-phase and neutral supply. The solid
neutral may be a detachable link.
c. Single-pole and switched-neutral circuit-breaker. A circuit-breaker having
one pole which is.fitted with an overcurrent release for connection in the phase
conductor and
dso a switch having contacts not intended to make or break
current.
This switch is arranged to be operated with the main pole of the circuit-
breaker, and to
close before and open after the main contacts, for the purpose
of isolating the neutral,
d. Single-pole and neutral circuit-breaker. A circuit-breaker having two poles,
oniy one of which is fitted with an overcurrent release, this being for connection
28
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31. BSI BSr387L: PARTxL b5 Lb24669 0052782 T =
B.S. 3871 : 1965
in the phase conductor of a singlephase and neutral supply. The other pole is
for connection in the neutral conductor.
e. Double-pole circuit-breaker. A circuit-breaker having two poles, each
fitted with an overcurrent release for connection in the
two conductors of a
single-phase supply.
Three-phase ad three-phase and neutral supplies
f. Triple-pole circuìt-breaker. A circuit-breaker having three poles each fitted
with an overcurrent release.
This arrangement is intended for use on a three-
phase supply, where control of the three phases is required to
be simultaneous
and where
a fault on one or more phases will resuit in isolation of the supply.
g. Triple-pole arid solid-neutral circuit-breaker. A triple-pole circuit-breaker,
as
hf, but with the addition of a solid conducting path with terminations to
allow connection
of the neutral conductor of a three-phase, four-wire supply.
The solid neutral may be a detachable link.
h. Tripleyole and switched-neutral circuit-breaker. A triplepole circuit-
breaker, as
in5 with the addition of a switch having contacts not intended to
make or break current.
This switch is arranged to be operated with the main
poles of the circuit-breaker, and to close before and open after the main con-
tacts, for the purpose of isolating the neutral in
a three-phase, four-wire supply.
j. Triple-pole arid neutral circuit-breaker. A circuit-breaker having four poles,
only thre of which are fitted with overcurrent releases.
"hese three poles are
for connection in the phase conductors, and the fourth pole in the neutral
conductor, of a three-phase four-wire supply.
A3. Service conditions. See Clause 3.
A4. Breaking capacity. The maximum breaking capacity of the circuit-breaker
should be adequate for the maximum prospective fault current at the place where
the circuit-breakers are to be installed in the supply system or network.
(See
also Appendix B re ' Back-up protection '.)
In many a.c. installations of miniature circuit-breakers, elaborate calcuiatìons
are
unnecessary for the following reasons:
a. The resistance and reactance characteristics of small transformers do not
vary appreciably between different makes and designs.
It is therefore possible
to
use common values from which the short-circuit current and power factor
can be calculated, assuming ,that the high-voltage network from which the
transformer is fed exercises no appreciable influence. ms assumption errs on
the safe side since any appreciable effect of the h.v. network would be to reduce
the 1.v. short-circuit current.)
29
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32. __ .li
BSI BS*387Ji: PART*L b5 Lb2Llbb7 0052783 L
B.S. 3871 : 1965
b. The connections between the supply transformer and the miniature circuit-
breaker may have
a considerable effect upon the values of the short-circuit
current and power factor.
For low-voltage cables the resistance value is the most
important factor, as the reactance is relatively small, and, by neglecting the
latter, the necessary measurements or calculations can be considerably simplified
without danger
to the circuit-breaker performance.
A5. Apparatus to be protected. The primary function of an m.c.b. is to protect
the installation.
For this reason the present standard lays down requirements for
the overcurrent device calibration and, furthermore, states that the circuit-
breakers shaii have
a fixed unadjustable time/current characteristic. To ensure
complete protection of the system conductors, the current rating of the circuit-
breaker should not, therefore, exceed that permitted in the current edition
of
the I.E.E. Wiring Regulations for the size of cable in question.
When,
in addition; it is desired to protect certain items of apparatus, the
apparatus
to be protected may be put into two general classes:
(i) Apparatus that imposes a load which does not vary much above its
rated value, e,g. heating apparatus. The circuits feeding such apparatus may
be called steady load circuits.
(ii) Apparatus that imposes
a foad which may have peaks of compara-
tively short duration about its rated value, e.g. motors, capacitors, trans-
formers and lighting apparatus, ali of which take a transient overcurrent.
Circuits feeding such apparatus may
be cailed fluctuating load circuits.
a. Miniature circuit-breakers for steady load circuits. If, as often happens,
circuit-breakers are the only protection in a steady load circuit, their current
ratings should
be at least equal to that of the apparatus. If other overcurrent
protection is provided,
or if discrimination requires it, a circuit-breaker of
greater current rating may
be permissible or necessary.
6. Circuit-breakers for juctuating load circuits. For fluctuating load circuits
the circuit-breakers should have tims/current characteristics that
will allow the
transient overcurrent to
be carried without tripping, For this purpose it my
sometimes be necessary to select circuit-breakers having a current rating greater
than that of the circuit.
For motor circuits it is necessary to obtain particulars of the magnitude and
duration
of the starting current, and to select circuit-breakers of the required
current rating by reference to the appropriate t¡me/cmmt characteristics.
Alternatively (and this is usually better) the problem should
be referral to the
manufacturer of the circuit-breakers
so that advantage may be taken of previous
experience.
Foi: capacitor circuits, transformer circuits, tungsten lighting circuits and
fluorescent lighting circuits, the circuit-breakers
may need to have current
30
.
AS
allered
1974
. -__1
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33. ~ ~~
BSI BS*387II: PART*II 65 W II624669 0052784 3 W
B.S. 3871 : 19G5
ratings greater that the nominal current of the apparatus to be protected. Again
the recommendation of the manufacturer of the circuit-breakers
is to be pre-
ferred to an inflexible ruling in such cases.
APPENDIX B
DISCRIMINATION
Miniature circuit-breakers are essentially devices for the protection
of sub-
circuits. The application
of miniature circuit-breakers in any medium or large
distribution network will usually result
in there being one or more protective
devices between the miniature circuit-breaker and the power source, These
protective devices may
be other circuit-breakers or high-breaking capacity fuses,
and
in each case it is desirable to estimate the degree of discrimination which
wili be obtained.
Furthermore,
if the fault Ievel at the point of application of the miniature
circuit-breaker is in excess Òf its breaking capacity it is necessary to provide
a
means of back-up protection. Although it is not the purpose of this Appendix
to deal with back-up protection as such, it should be realized that satisfactory
discrimination between
a smaller and a larger device does not necessarily
amount to provision of back-up protection by the larger device. This can only
be achieved if the larger device has an energy limiting feature. It follows that a
circuit-breaker normally does not provide back-up protection for
a miniature
circuit-breaker.
On the other hand, a high-breaking-capacity fuse may be used
for such duty provided that its normal current rating does not exceed such
definite maximum value-as published by the miniature circuit-breaker manu-
facturer. It must
be appreciated that this maximum value will depend on the
make and type of fuse.
B1. Discrimination between miniature circuit-breakers. A miniature circuit-
breaker is normally provided with both an inherent time delay and an instan-
taneous trip device. The former operates
on small overcurrents, and has an
inverse time/current Characteristic which is
a function of the normal current
rating, whereas the latter operates
on severe overcurrents and short-circuits,
and has a total operating time of about
10 milliseconds.
It follows that where there are two miniature circuit-breakers of differing
current ratings in series
:
a. At currents below the value at which the higher rated miniature circuit-
breaker trips instantaneously, the miniature circuit-breaker
of lower current
rating will discriminate against that of higher rating. This can
be readily ascer-
tained by a comparison of the time/current characteristic curves of the devices
concerned
(see Fig. 12).
31

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34. BSI BS*:3871: PART81 65 W L624bb9 0052785 5 I
BOS. 3871 : 1965
6. At currents above the value at which the higher rated miniature circuit-
breaker trips instantaneously, discrimination will not be achieved.
B2. Discrimination between miniature circuit-breakers and other circuit-breakers.
Exactly the same provisions apply as for the miniature circuit-breakers in Sub-
clause
I above.
B3. Discrimination between miniature circuit-breakers and high-breaking-capacity
fuses. Due to the levelling-off of the miniature circuit-breaker timelcurrent
characteristic curve at the limiting total operating time of approximately
10
milliseconds (1/2 cycle) the pre-arcing timelcurrent characteristic curve of the
high-breaking-capacity fuse crosses the former along its limiting line: this
' crossover point ' defines the degree of discrimination obtainable.
a. At currents below the crossover point the miniature circuit-breaker will
discriminate against the fuse. This can be readily ascertained by a comparison
of the time/current curves of the devices concerned (see Fig.
13).
6. At currents above the crossover point, discrimination will not be achieved.
NOTE. It must be appreciated that in all the foregoing, the instantaneous trip currents and
crossover Roints cannot
be determined with absolute accuracy so that, in fact, there will be
a marginal area where discrimination is somewhat uncertain.
APPENDIX C
NOTES ON TERMINOLOGY
C1. Operating characteristics. The time/current characteristics (see Clause 13)
of miniature circuit-breakers are illustrated typically in Fig. 8 and are of value
in connection with the selection of miniature circuit-breakers,
see Appendix A.
In the determination of the timelcurrant characteristics, the miniature circuit-
breakers start from approximately ambient temperature (i.e. a temperature
generally
less than 25'C) and have not been carrying current prior to the test.
C2. Current rating. The term current rating applied to a miniature circuit-
breaker is synonymous with the terms
normal current, current carrying, capacity
etc,, used for other electrical apparatus. The current rating is assigned by the
manufacturer from the results of tests made in accordance with Clauses
12,
30 and 31.
C3. Calibration. Circuit-breakers constructed in accordance with this
specification, are set to trip at a sustained
35 per cent or 50 per cent (see
Table
5) overcurrent within a given time at a specified ambient temperature.
At smaller values
of overcurrent they will either not trip or will only trip after
an indeterminate time.
32
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35. ~~ ~
-~
BSI BSr3871: PARW1 65 1624669 0052786 7 II
B.S. 3871 : 1965
APPENDIX D
-OPERATION ON SHORT-CIRCUIT
In tests for duty, current and voltage are usuaiiy heasured on an oscillograph.
The full
kes in Fig. 9 are typical of current and boltage traces when breaking
a fault on short circuit. The dotted line markedprokpective current
on the current
trace represents the current that would have flowed had it not been limited by
the internal impedance of fhe circuit-breaker toa the value represented by the
full line marked
actual current.
Complete isolation of the circuit in which a fault has been present usually
occurs at the Grst
or second instant of zero current following initiation of the
fault. Whether this occurs at the
first or second instant of zero current is de-
pendent
on the point on the voltage wave at which the fault is initiated. The
minimum total operating time usually varies bhween
% and 5/s of a cycle and
is often referred to
as ' half cycle ' operation. .
The values of power factor given in this spekification are those assigned to a
testing circuit. They represent values that nihy
be obtained on short-circuit
conditions in service, and should not be confused with the power factor of a
circuit when it is carrying nomal current.
r
,
APPENDIX: E
MEASUREMENT OF PROSPECTIVE CURRENT OF
TEST DUTY CIRCUIT'
Prospective current is measured (as a preliminary to a test for duty) in a circuit
irl which a link of negligible impedance is used in place of the circuit-breaker.
In an a.c. circuit, current is usually measured as the r.m.s. value of the sym-
metrical constant-amplitude wave form it reaches shortly after the circuit is
made. The time between the making of the circuit and the reaching of the
measured value usually depends only on thje time-constant of the
d.c. component
of the transient asymmetrical current.
The initial magniâude of the d.c. component
(or the degree of asymmetry)
in any circuit depends on the power factor of the circuit and on the point on the
I
33
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36. -
BSI BS*3872: PART*L 65 m Lb24bb9 0052787 9 m
B.S. 3871 : 1965
voltage wave at which the circuit is made. The rate at which the d.c. component
falls from its initial magnitude depends on the power factor of the circuit.
The current obtained in an a.c. prospective current test may or may not reach
a constant amplitude wave form. If it does so in a time comparable with the
time-constant of the d.c. component
of the transient asymmetrical current, the
r,m.s. value of the constant amplitude wave form, measured by an ammeter
or otherwise, is the prospective current of the test circuit.
If the required current is large it is usually not possible to obtain a constant
amplitude wave form
in an a.c. prospective current test, because of charac-
teristics inherent in the source of power for the test or because of limitations
imposed on the operation of large current a.c. testing equipment. In these cir-
cumstances the prospective current is measured
as the r.m.s. value of the alter-
nating component of the current over a stated period of time; the arbitrary
period usually taken is the first 0.02 second after the making of the circuit. In
practice it is usually suíñciently accurate to make this measurement in the way
indicated
ia the next paragraph.
An oscillogram of the current is taken (see Fig. 10) and on this oscillogram:
a. AA, and BB, are drawn as the envelope of the current wave.
b. nie point O corresponding to the current when the circuit is made, is
marked, and the current zsro line is produced from
O to F, where F corresponds
to a time
0.01 second after O (i.e. midway between O and 0.02 second after the
circuit is made).
c. GH is drawn through F perpendicular to the current zéro line to intersect
AA, and BBI at G and H respectively.
The prospective current during the ikst
0.02 second after the making of the
circuit is deemed to
be given by GH/2i2.
APPENDIX F
COMPUTATION OF POWER FACTOR FROM OSCILLOGRAMS
The power factor of an alternating current circuit is computed from osciiio-
grams
in accordance with the following methods:
Method 1. if the asymmetry of the prospective current is sufficient, the power
factor may
be determined from the curve of the d.c. component of the pros-
pective current wave as folIows:
34
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37. ?
BSI BS*387lt: PART*L 65 m Lb24669 0052788 O m
B.S. 3871 : 1965
a. Determine the time constant T of the d.c. component, which has the
general form:
id = Zdoe-t/T
where id is the value of the d,c. component at any instant,
Ido is the initial value of the d.c. component,
T is the time constant in seconds of the test circuit,
f is the time interval in seconds between id and Idop
and e is the base of Naperian logarithms.
This can readily
be done as follows:
(i) Measure the value of
Ido (i.e. the initial value), and the Value of id
(ii) Determine the value e-*/= by dividing id by Ido.
(iii) From a table of emX determine the value of x corresponding to the
ratio
id/Ido.
(The value of emX can be obtained re ily from a table of Naperian
logarithms by taking the reciprocal
f f the number of which x is the
I
(iv) The value x represents t/T and so T can be determined by dividing
6. Determine the angle I# from $ =arc tan wT, where w is the actual
at any other time
t.
logarithm.)
t by x.
frequency multiplied by 27r. The power factor is then cos 9.
Method 2. For the higher values of power factor the asymmetry is likely to be
insuíñcient for an accurate determination of T, and this alternative method
should then
be used; it requires a voltage trace in addition to a prospective-
current trace, as shown in Fig.
11. The part of the current wave at which the
asymmetry, if any, has disappeared is determined by comparison of the duration
of the current-loops.
Thus asymmetry has disappeared at A, since AB = BC.
A distance AD is then stepped back along the current-loops, making AD equal
to
AB; it may be necessary to do this more than once. A projection E on the
current
zero is then made from the point F, which represents the last voltage
zero before the initiation of the current.
Then
ED, to the appropriate scale, is the angle 4 and the power factor is
cos
5.
APPFNDIX G
MEASUREMENT OF RECOVERY VOLTAGE
The recovery voltage is the normal frequency r.m.s. voltage that exists between
the poles of a circuit-breaker after ha1
arc extinction.
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38. I
. BSI BSm387L: PART*kL 65 = Lb24b69 0052789 2
B.S. 3871 : 1965
For tests on single-phase circuit-breakers in accordance with Figs. 2 and 5,
the recovery voltage is measured directly across the individual circuit-breakers,
and the measured value is the recovery-voltage for the test.
For three-phase tests in accordance with Figs. 1,3 and 4 the recovery voltage
may
be measured directly across each phase.
Aiternatively,
if being recorded by oscillograph, it may more conveniently
be measuied by recording the voltages, Vr, across each of the three circuit-
breakers. The recovery voltage
is then the average of the three values of Vr SO
obtained, multiplied by the phase factor, 1.73.
For tests of three-pole or four-pole circuit-breakers in accordance with
Fig.
6, the recovery voltage is obtained by measuring the recovery voltage
across each of the three active poles, and multiplying the average
of the three
values
so obtained by the phase factor, 1.73.
APPENDIX H
INFORMATION TO BE WCLUDED IN RECORDS OF TYPE T"s
FOR SHORT-CIRCUIT CAPACITY RATINGS
1. Generai.
u. Date of tests.
b. 'Reference or report number.
c. Test numh.
d. Osciiiogram numbers.
2. ApparatusMed.
u. Type or list number.
b. Manufacturer's description.
c. Name of manufacturer.
d. Photograph numlys.
e. Drawing numb, with dates and issue number.
3. Raw assigned by the manufacimer.
u. Number of poles.
b. Voltage.
c. Normalcurrent.
d. Frequency.
e. Short-circuit capacity (prospective current).
f. Operatingduty.
g. Type, according to instantaneous tripping current.
36
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39. BSI BS*387L: PART*L b5 = Lb2Libb9 0052790 9
B.S. 3871 : 1965
4, Test conditions.
u. Number of poles.
6. Power factor.
c. Frequency.
d. Diagram of COM~C~~O~S.
5. Specincation. Tests to be made in accordance with this British Standard.
6. Short-circuit capacity tests (see Ciause 30).
a. Operation and time intervals.
b. Appìied voltage.
c. Prospective current.
d. Recovery voltage.
e. Total operating time.
f. Physical behaviour.
(i) Flame emission (see Ciause 30).
(ii) Behaviour, condition after test, insulation resistance and remuits.
37
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40. BSI BSx3871: PART*3 b5 LbSLtbb9 0052793 O =
B.S. 3871 : 1965
38
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41. BSI BS*387L: PART81 65 I 1b24bh7 0052772 2 =
B.S. 3871 : 1965
39
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42. BSE BS*387L: PART*L b5 L624667 0052793 Li =
B.S. 3871 : 1965
40
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43. BSI BS*3872: PART*& b5 3624bb9 0052794 b M
B.S. 3871 : 1965
41
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44. BSI BS*3B7&: PART*& h5 L62Yhh9 0052795
B.S. 3871 : 1965
1
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45. B.S. 3871 : 1.965
43
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46. 75 mm crs
Flexible cable holder
/
r-L-1 Test
j 11
circuit-
I breaker
L- -J
1.5mm2 ca~e
--T
: BSI BSx387L: PARTxL 65 W Lb2Ltb69 0052797 L M
B.S. 3871 : 1965
As
altered
Nov.
I974
---- 9
~~ ~- -.y
single ~OC:! oí
0.5 mm2 twisted
twin
flexible cord

2 -10 mm sq. brass
each 50 mm long
-terminal Mocks,
Insulating
base
+
Tapped for
M 3 screws
/
Detail of
cable holder
2 holes,
drill 3 mm dia.
Fig 7. Flexible cord test
44
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47. BSI BS*3B72: PART*L 65 W 2624664 0052798 3 W
B.S. 5871 : 1965
I
I-
Multiples of rated current
Fig. 8. Typical MCB time/curreat characteristic
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48. BSI BSx387L: PARTxL b5 LbZ4bb9 005Z797 5 =
B.S. 3871 : 1965
Prospective Current
Actual current
Current
pis. 9. miral osculogram of operetion under short-circuit break cooditioos
-v
.--_-
'i6
-
-...
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49. BSI BS*38?L: PART*L 65 m Lb24667 0052800 8 m
B.S. 3871 : 1965
47
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50. --__
BSI BS*3871i: PART81 65 W 1624669 005Z801i T W
B.S. 3871 : 1965
Q,
E
I-
.-
u
E
%
0
Fig. 12. Comparative time/current characteristic curve^ for MCB’s of different ratings
I E
I-
t!
VI
E
O -
Current
b.
Current
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51. BSI BS*387L: PARTS1 65 m 1624669 0052802 L m
. B.S. 3871 : 1965
AdjustaMe bard
I
I-
200 mm
I80 mm I
20 mm
As
altered
Nov.
1974
300 mm
Hinged wooden
,platform
Metal
stop
plate
Concrete
Mock
400 mm
Slots
NOTE The supplementary mass is provided to ensure that the moment of inertia of
the complete system is practically constant.
49
Fig. 14. Shock tat 8ppulius
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52. BRITISH STANDARDS
The foliowing are available on application:
YEARBOOK
Including subject index and numerical list of
British Standards
SECTIONAL LISTS. Gratis
Acoustics
Aircraft materiais and components
Building materials and components
Chemical engineer&
Chemicals, fats, oils, scientific apparatus, etc.
Cinematography and photography
Coal, coke and colliery requisites
Codes of Practice
Consumer pods
Documentation, including Universal Decimal Classification
Drawing prâctice
Electrical engineering
Farming, dairying and allied interests
Furniture, bedding and furnishings
Gas and solid fuel and refractories
Glassware including scientific apparatus
Hospital equipment
Illumination and lighting fittings
Industrial instruments, etc.
Iron and steel
Machine tools
Mechanical engineering
Nomenclature, symbols and abbreviations
Non-ferrous metals
Packaging and containers
Paints, varnishes, paint materials and colours for paints
Personal safety equipment
Petroleum industry
Plastics
Printing, paper and stationery
Road e,ngineering
Rubber
Shipbuilding
Textiles and clothing
Welding
Applications should be addressed to:
BRITISH STANDARDS INSTITUTION
Sales Administration
Linford
Wood, Milton Keynes MK14 6LE
(Telephone Milton Keynes
[phone])
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53. BSI 6S*3871: PART81 b5 Lb24667 0052804 5 m
BRITISH STANDARDS INSTITUTION
The British Standards Instifution was founded in 1901
and incorporated by Royal Charter in
1929.
The principal objects of the Institution as set out in
the charter are to Co-ordinate the efforts of producers
and users for the improvement, standardization and
simplification of engineering and industrial materials;
to simplify production and distribution; to eliminate
the waste
of time and material involved in the pro-
duction of an unnecessary variety of patterns and sizes
of articles for one and the same purpose; to set up
standards
of quality and dimensions, and to promote
the general adoption of British Standards.
In carrying out its work the Institution endeavours
to ensure adequate representation of all viewpoints.
Before embarking on any project it must be satisfied
that there is a strong body of opinion
in favour of
proceeding and that there is a recognized need to
be met.
The Institution is
a non-profit-making concern. It
is financed by subscriptions from
firms, trade asso-
ciations, professional institutions and other bodies
interested in its work, by a Government grant and
by
the sale of Its publications. The demands. on the
services of the Institution are steadily increasing and
can only
be met if continuing and incr,eased financial
support is provided.
Membership of the Institution is open to British
subjects, companies, technical and trade associations,
and local and public authorities.
.
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54. AMD 6431
Type
Amendment No. 4
published and effective from 30 March 1990
to BS 3871 : Part 1 : 1965
Specification for miniature and moulded case circuit-breakers
Part
1. Miniature air-break circuit-breakers for a.c. circuits
instantaneous Qipping current
Revised text
NOTE. This amendment is being published to incorporate the magnefic fripping
characteristics of types
B, C and D circuit-breakers from the draft CENELEC Standard,
EN 60898
: Circuit-breakers for overcurrent protection for household and similar
installations.
Table 2. Types of circuit-breaker according to instantaneous tripping current
(as amended by Amendment
No. 3). Delete the existing Table 2 and
substitute the following.
1
2
3
4
B' -
C
D
hP
> 2.71n,< 4.01,
> 4.OIn,< 7.01,
> 7.01n,<10 In
>10 In,<S0 I,
> 3 In,< 5 In
> s I,,<lO 1,
>10 In,<20 In
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55. . BSI BS*387L: PARTxL 65 Lb24bh7 005Z8Ob 9 =
Test
current
Amp
1.0 I,
1.5 In
1.35ín
2.5
I,
2.7 In
4.0 In
4.0 In
7.0 In
7.0 In
10 I,
6.0 In
10 In
50 In
1.5 I,,
0.9 In
1.131,
1.131,
1.451,
1.45
In
1.751,
1.131n
1.131,
1.9
In
1.9 In
In
I,
2.551,
2.551,
2.551,
3
rn
5 In
10 In
10 In
20 ln
5 In
Table 5. Operating duties (as amended by Amendment No. 3). Delete
the existing Table
5 and footnotes and substitute the foliowing.
TABLE 5. OPERATING DUTIES
Test Result Ambient temperature
period
Reference Reference Reference
calibration calibration calibration
temperature temperaNre temperature
20 OC* 30 OC* 40 OC*
hlin. Max. Min. Max. hlin. hiax.
OC OC Oc OC OC "C
2 h No trip 20 25 40 45
~ 1 h Trip 20 25 40 45
1 h Trip 20 25 40 45
1 s-60s Trip 20 25 40 45
0.1 s No trip 20 25 40 45
0.1
s Trip 20 25 40 45
0.1
s Notrip 20 25 40 45
0.1 s Trip 20 25 40 45
0.1 s No trip 20 25 40 45
0.1
s Trip 20 25 40 45
10s
Trip 20 25 40 45
0.i s Notrip 20 25 40 45
0.1
s Trip 20 25 40 45
1 h Trip o5 20 25
1 h Trip o5 20 25
2
h Notrip 34 36 54 56
1 h . Notrip 30 35
2
h No trip 30 35
1 h Trip 30 35
2
h Trip 30 ' 35
1 h No trip -1 -3
2 h No trip -1 -3
1 h Trip -7 -3
2 h Trip -7 -3
1 h No trip 38 42
2h No trip 38 42
1 s No trip 30 ' 35
1 min Trip 30 35
Zmin Trip 30 35
0.1 No trip 30 35
0.1
s No trip 30 35
0.1
s Trip 30 35
0.1
s No trip I 30 35
0.1
s Trip 30 , 35
0.1
s Trip 30 35
Type of
instantaneous
opera
tion
1234
1234
1234
it 2j 3j 4t
1
li
2
2:
3
3f
4
4
1234
1234
1234
BCD
BCD
B C D$
B C D$
BCD
4t
BCD
B C Dt
~ BCD$
BCD
Cj
D
Dt
(Rated
current,
In
Amp
AU ratings
4 10
> 10
AU ratings
AU ratings
AU ratings
AU ratings
AU ratings
Aiiratings
AU ratings
AU ratings
AU ratings
AU ratings
c 10
> 10
AU ratings
4 63
> 63
4 63
> 63
4 63
> 63
4 63
> 63
< 63
> 63
AU ratings
4 32
> 32
AU ratings
AU ratings
AU ratings
Ail ratings
AU ratings
AU ratings
*The reference calibration temperature for types
B, Cor D shall be 30 'Cand for types 1, 2,3 and 4 shall be either
20 OC or 40 OC, the purpose of the latter value being to avoid the necessity of de-iating thermally sensitive circuit-
breakers which are to be mounted in enclosures.
tThese tests are repeated
in Table 8.
$See Clause. 24.
2
-
AMD 6431
7
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56. BSI BS8387L: PART81 65 = L62qbbî 0052803 O
Circuit-breaker
current rating
A
516
10
15/16
20
25
30132
40
45
50
60/63
100
Cable size
One- and two-pole
circuit-breakers circuit-breakers
mm2 mm’
1 1
1.5 1.5
2.5 2.5
2.5 4
4 4
6 6
10 10
10 10
16 16
16
25
35 35
Three- and four-pole
Delete the sentence under the original Table 7 and substitute the following
under the new Table
7.
‘The length of cable used to conneet the circuit-breaker to the test circuit
shall not exceed a total of 1.2
f 0-05 m per pole.
For circuit-breaker ratings not specified in Table
7 the cable size for the
next higher rating shall be used.’
3 AMD 6431
J ,
7
/--
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57. - BSI BS*387L: PART*i 65 - Lb24bb9 0052808 2
Clause 24. Overcurrent device calibration test. Insert the following at the end
of paragraph
2 after ‘case’.
‘, except for the tests at I .45 in or 1.9 In on types B, C and D which shall
follow the tests at
1 .I3 in at the same ambient temperature within 5 seconds.’
Clause
25. Time/current characteristic test (as amended by Amendinent
No. 3). Delete paragraph 2 and subsfitute the following.
‘The lowest
of the currents shall be not greater than 1 .O5 times the
minimum tripping current
of the circuit-breakers as specified in Table 5 and
the highest of the currents shall cause the circuit-breakers to trip in not more
than
0.1 s.’
Clause 30. Short-circuit capacity tests (general) (as amended by Amendment
No. 3). In subclause a delete line 1 and substitute the following.
‘For circuit-breakers, types 1,2,3 and 4, samples submitted for this test
shall have been tested to check that they’.
Insert the following new paragraph after paragraph 1.
‘For circuit-breakers, types
B, C and D, sainples submitted for this test shall
have been tested to check that when a current of 1.13
In is passed through all
poles for the time specified in Table
5, the circuit-breaker does not trip and
when the current is then increased within 5
s to 1.45 In the circuit-breaker
shall trip within the time specified in Table 5
.’
Clause 30. Short-circuit capacity tests (general). In subclause e, insert the
following at the end
of sentence 2 after ‘current’.
‘on the final MB operation in a sequence’,
Clause
32. Flexible cord test (as amended by Amendment No. 2). In the title,
delete
‘5 amp’ and substitute ‘6 amp’.
In lines 5 and 6, delete ‘Table 8, BS 6500 : 1969’ and substitute ‘Table 15,
BS 6500.: 1984’.
In paragraph 4, line 4, delete ‘BS 6004 : 1969’ and substitute ‘BS 6004 :
1984’.
4
AMD 6431
-
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58. a BSI BS*3ô3\L: PART*icL 65 W Lb24669 00528Ö7 4 W.
Table 8. Operating duties for routine tests. Delete the existing Table 8 and
notes and substitute the following.
5Pe of
instantaneous
operation
1234
1
2
3
4
BCD
BCD
BCD
B
C
D
Rated
current,
In
hP
Ail ratings
All ratings
All ratings
All ratings
All ratings
Ail ratings
<32 A
>32 A
All ratings
Ail ratings
All ratings
Test
current
"p
< 2.5 In
4.0 I,
7.0 In
10 I,
50 I,
2.55 In
2.55 In
2.55 I,
5 In
10 I,
20 In
Test
period
1 s-60s"
0.1 s
0.1 s
0.1 s
0.1 s
1 s*
1 min*
2 min*
0.1 s
0.1 s
0.1 s
Result
Trip
Trip
Trip
Trip
Trip
No trip
Trip
Trip
Trip
Trip
Ti-ip
*These values can be amended to ensure that the requirements of Table 5
are met for breakers when tested at their reference calibration temperature.
NOTE. The values in this Table are extracted from the values given in
Table 5.
9003-2-1.2k-B
,
.Y -.
5
AMD 6431
PFLIII ,
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