RCD Operation Training Lecture Lagos Nig.

RCD Operation

3. Content
•Operating principles of RCDs
•Types of RCDs
•Circuit arrangement of RCDs
•RCD current rating
•Wiring rules requirements concerning RCDs
•RCD selection

4. Inside a RCD

5. Inside a RCD
Toroidal Transformer
Tripping Relay

6. Trip Relays
Three Types
•Magnetically Held
•Electronic
•Electro-mechanical

7. Magnetically Held
•Magnet holds trip circuit closed against a spring
•Fault causes a current to flow in a coil around magnet
•Magnetic field is reduced
•Spring is stronger than magnetic field and trips breaker
•Polarised
•Saturation
Trips on +ve cycle only
Trips on both +ve and –ve of the cycle

8. How a RCD Works With a Fault

9. How a RCD Works With a Fault

10. What Must A RCD Do?
•Detect leakage current up to its rated value
•Switch of rapidly when such leakage current is detected
•Ignore leakage currents 50% below its rated value
•Discriminate between earth leakage current and other
line disturbances

11. Causes of Unwanted Tripping
•Standing Leakage Currents
•Electrical Disturbances
•Installation practices & Faults

12. Standing Leakage Currents
Is insulation is perfect?
AS/NZS 3000:2007
Clause 8.3.6.2
Page 321
1MΩ
230V
= 0.23 mA
Class Iappliances may legally have up to 5mA
What about sheathed heating elements?
AS/NZS 3000:2007
Clause 8.3.6.2
Page 321
0.01MΩ
230V
= 23 mA

13. Electrical Disturbances
Caused by:
•Lightning strikes
•Switching transients
Natural
Manmade

14. Lightning Strikes
Generally cause transients in the form of:
•High Voltage
•High frequency

15. Switching Transients
What happens when a
magnetic field changes?
Generation of:
•High Voltages
•High frequencies
Reduce the X
cof the circuitf
I
X
c cX
V
I
Leakage current increases
Two insulated conductors running together

16. Switching Transients
•Starting induction motors have a very low PF
•High inrush currents

17. Relay Types
TypeI
RCDs and relays with a trip current (I
Δn)
not exceeding 10 mA.
Found in high risk areas such as:
•Hospitals
•Doctors rooms
•Dialysis rooms
•Dentists rooms
•Kindergartens

19. Relay Types
TypeII
RCDs and relays with a trip current (I
Δn)
exceeding 10mA but not 30mA
General purpose:
As per AS/NZS 3000:2007

21. Relay Types
TypeIII
RCDs and relays with a trip current (I
Δn)
exceeding 30mA but not 300mA
Time Delay
But without “Selective Tripping”

23. Relay Types
TypeIV
RCDs and relays with a trip current (I
Δn)
exceeding 30mA but not 300mA
Time Delay
With “Selective Tripping”

25. But What Type of Current?
Type and shape of current will affect the tripping
time of an RCD AS/NZS 3000:2007
Clause 2.6.2.2
Page 97
ACGuaranteed for only AC operation
AWill take some pulsating DC current
BAC up to 1000Hz, pulsating DC, and DC
SSelective RCD

26. RCD Housings
Does not trip due
to over current
2 Pole

27. Connecting a 2 Pole RCD
Neutral link Protected Neutral link

28. 4 Pole RCD

29. Single Phase Circuit
X2
OR
3 Phase + Neutral
Note
Some RCDs are Polarised

30. RCD Power Point

31. Combination RCD MCB

32. RCD + MCB
OR
RCD/MCB
= 3 Modules
= 2 Modules

33. Toroidal RCD
Output Used to supply Trip
Coil on a Circuit breaker