Electrical System Design, Classifications

The electrical installations are classified
according to the classification of voltages as
• Low voltage installation
• Medium voltage installation
• High voltage installation
• Extra High voltage installation

1. Electrical Design

2. Classification of Voltages
Standard voltages are classified in NEC as follows

–Low voltage (less than 250 V)
–Medium voltage (250 V to less than 650 V)
–High voltage (650 V to less than 33kV)
–Extra high voltage (33 kV)

3. The electrical installations are classified
according to the classification of voltages as
•Low voltage installation
•Medium voltage installation
•High voltage installation
•Extra High voltage installation

4. Standard declared voltages
•240 V ( single phase 2 wire system)
•415 V (three phase 4 wire system)
•3.3kV, 6.6kV, 11kV, 22kV, 33kV, 66kV, 132kV,
220kV, 400kV (line to line voltage)

5. Voltage limits for AC system
•The voltage at any point of the system under
normal condition shall not depart from the
declared voltage by not more than the below
values
•Low and medium voltages - 6 %
•High voltage - 9 %
•Extra high voltage - 12.5 %

6. Difference between neutral wire and
earth wire

7. Classification of supply systems
•T.N. Systems
–In this system 1 point is directly earthed
–The exposed conductive parts of electrical
installations are connected to that point by
protective conductors.

8. T.N. – S System

9. •T – direct connection of one point to earth
•N –neutral of ac
•S – neutral and protective functions provided
by separate conductors
•PE – power system earth

10. T.N.C. – S System

11. T.N.C.-S system

12. T.T. system

13. •T.T. Systems
–The power system has one point directly earthed.
–The exposed conductive parts of the installations
is connected to separate earth electrode which is
electrically independent of the earth electrode of
the power system

14. I.T. Systems

15. •No direct connection between live parts and
the earth
•The exposed conductive parts of electrical
installation being directly earthed.

17. Classification of buildings & building
services
•Domestic buildings
•Office /business buildings
•Shopping /commercial buildings
•Educational buildings
•Recreational /assembly buildings
•Other buildings

18. Electric services in buildings
•The nearness of supply point
•Position in the building
•Characteristics of supply (ac or dc)
–Number of phases, voltage levels, power ratings of
equipments and accessories.
•Maximum load demanded/anticipated
•Alternative power supply
•Guidelines of the supply authority are to be followed.

19. Rating of different luminaries

20. Number of points for building units

21. Recommended schedule of socket
outlets

22. WIRING ACCESSORIES AND ITS
SPECIFICATIONS

23. Wiring accessories and its
specifications
•AC Energy meter
–Phase : Single, three phase, three phase 4 wire
–Rated voltage: 240 V, 415 V
–Frequency : 50Hz
–Type: Induction type/Electronic

24. Ceiling fan
•Name of the firm
•Number of blades :
•Size of blade sweep : 36’’, 48’’, 56’’
•Type : AC/DC
•Rated voltage : 240V, single phase
•Frequency : 50 Hz
•Power factor : 0.8 0.9 etc
•Speed : 450 rpm
•Power consumption : 60 W, 100 W etc
•Type of regulator: resistance, eletronic

25. Tumbler switch
•Rating : 5A
•Control : single/two ways
•Construction material : bakelite with porcelain
base
•Type : surface
•Voltage : 250V

26. Main Switch: Single phase
•Make : IC (iron clad)
•Rating : 5A/15A/30A/40A/60A etc
•Voltage grade : 250V
•Fuse : one fuse with a neutral link

27. Main switch (3 phase)
•Make : IC (iron clad)
•No of poles : 3 poles with a neutral link
•Rating : 30A/60A100A/200A/300A
•Voltage grade : 500V

28. Distribution board (single phase)
•Make : IC (iron clad)
•Ways : two/three/four/five/six
•Ratings : 15A/30A/60A/100A etc
•Voltage grade: 250 V

29. Distribution board (3 phase)
•Make : IC (iron clad )
•Voltage grade : 500 V
•Bus bars : 3 phase/with or without neutral bus
•No of circuits: two ways to fifteen ways

30. Fuse carrier
•Fuse carrier : made of porcelain
•Voltage grade: 250V/500V
•Rated current : 15A/30A/60A/100A/200A

31. Fuse wire
Current rating (amp) Gauge of the fuse wire
3 38
5 35
10 29
15 25
24 22
32 20
45 18
102 14
High Rupturing Capacity (HRC) fuses
Current rating ( Amperes)
1 2 3 5 10 16 32 63 100 160 200 250 300 400 600 800

32. Socket outlet (Flush type)
•Current rating : 5 A/15A
•Voltage grade : 250V
•Contact : 2 pin, 3 pin
Plug
•Current rating : 5 A/15A
•Voltage grade : 250V
•Contact : 2 pin, 3 pin

33. Ceiling rose
•Type : 2 ways, 3 ways (2 plate, 3 plate)
Conduits
•Material : mild steel/PVC
•Size : 15mm dia, 20 mm dia, 30 mm dia, 35 mm dia etc

34. Choke for fluorescent tube
•Wattage (electromagnetic): 40W/20W
•Voltage grade : 250V
Starter for fluorescent tube
•Wattage : 40W/20W
•Voltage grade : 250V
•Type : glow type

35. Electric heater
PVC insulated cables (domestic)
•Voltage grade : 250V
•Conductor : copper /aluminium
•No of cores: single core/twin core/three core and 3½
core etc
•Wattage : 200/500/1000/2000W
•Voltage grade : 250V
•Type : coil type

36. Under ground cables (UG)
•Insulation : PILC/ XLPE
•Conductor : aluminium /copper
•Voltage grade : 6.6 kV, 33 kV
•No of cores : 3, 3½ core
•Size of conductors: 25mm², 35mm², 50mm²,
95mm², 120mm², 300mm², 400mm²

37. Miniature circuit breaker (MCB)
•Voltage rating: 240V/415V AC, 220V DC
•Current rating: 0.5A to 3 A
•No of poles: 1+N, 2,3,3+N,4
•Short circuit
–Breaking capacity: 9 kA
–Rated frequency : 50Hz, 60Hz
–Electrical endurance: more than 50,000 operating cycles
–Mechanical endurance: more than 100,000 operating
cycles
–Permissible ambient temp : 0.5 to +55˚C
–Connection conductor size : 35mm²

38. Load line Moulded Case Circuit
Breaker (MCCB)
•Voltage rating: 415V AC
•Current rating: 0.5A to 3 A
•No of poles: 2,4
•The load line G frames and A A frames MCCB’s
are available in single pole, three pole and
three pole with switched neutral

39. Earth leakage circuit breaker
(ELCB)
•Current rating: 25A,40A,63A for 4 pole
• 16A,25A,40A for 2 pole
•Nominal voltage: 240V/415V, 50 Hz
•Short circuit withstand capacity: 6000A
•Sensitivities : 300mA, 100mA,300mA
•Electrical life: 10,000 operations
•Mechanical life : 1 lac operations
•Ambient temperature: -5˚C to +60˚C
•Connecting terminal : 1.5 – 25 mm² condutors
•Protection class : IS – 2147
•Terminations : Flexible upto 25 mm² for 2 poles and 4 poles