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Saturday, 3 May 2014

12 electrical thumb rules to follow:

1. Transformer earthing wire / Strip size

Size of T.C or DGBody EarthingNeutral Earthing
<315 KVA25×3 mm Cu / 40×6 mm GI Strip25×3 mm Cu Strip
315 KVA to 500 KVA25×3 mm Cu / 40×6 mm GI Strip25×3 mm Cu Strip
500 KVA to 750 KVA25×3 mm Cu / 40×6 mm GI Strip40×3 mm Cu Strip
750 KVA to 1000 KVA25×3 mm Cu / 40×6 mm GI Strip50×3 mm Cu Strip


2. Motor earthing wire / Strip size

Size of MotorBody Earthing
< 5.5 KW85 SWG GI Wire
5.5 KW to 22 KW25×6 mm GI Strip
22 KW to 55 KW40×6 mm GI Strip
>55 KW50×6 mm GI Strip


3. Panel earthing wire / Strip size

Type of PanelBody Earthing
Lighting & Local Panel25×6 mm GI Strip
Control & Relay Panel25×6 mm GI Strip
D.G & Exciter Panel50×6 mm GI Strip
D.G & T/C Neutral50×6 mm Cu Strip


4. Electrical equipment earthing

EquipmentBody Earthing
LA (5KA,9KA)25×3 mm Cu Strip
HT Switchgear50×6 mm GI Strip
Structure50×6 mm GI Strip
Cable Tray50×6 mm GI Strip
Fence / Rail Gate50×6 mm GI Strip


5. Earthing wire (As per BS 7671)

Cross Section Area of Phase, Neutral Conductor(S) mm2Minimum Cross Section area of Earthing Conductor (mm2)
S<=16S (Not less than 2.5 mm2)
16<S<=3516
S>35S/2


6. Area for transformer room: (As per NBC-2005)

Transformer SizeMin. Transformer Room Area (M2)Min. Total Sub Station Area( Incoming HV,LV Panel, T.C Roof) (M2)Min. Space Width (Meter)
1 x 16014909
2 x 1602811813.5
1 x 25015919
2 x 2503012113.5
1 x 40016.5939
2 x 4003312513.5
3 x 40049.516718
2 x 5003613014.5
3 x 5005417219
2 x 6303613214.5
3 x 6305417619
2 x 8003913514.5
3 x 8005818114
2 x 10003914914.5
3 x 10005819719
- The capacitor bank should be automatically switched type for substation of 5MVA and higher.
- Transformer up to 25 KVA can be mounted direct on pole.
- Transformer from 25 KVA to 250KVA can be mounted either on “H” frame of plinth.
- Transformer above 250 KVA can be mounted plinth only.
- Transformer above 100 MVA shall be protected by drop out fuse or circuit breaker.


7. Span of transmission line (Central electricity authority)

VoltageNormal Span
765 KV400 to 450 Meter
400 KV400 Meter
220 KV335,350,375 Meter
132 KV315,325,335 Meter
66 KV240,250,275 Meter


8. Max. lock rotor amp for 1-phase 230V motor (NEMA)

HPAmp
1 HP45 Amp
1.5 HP50 Amp
2 HP65 Amp
3 HP90 Amp
5 HP135 Amp
7.5 HP200 Amp
10 HP260 Amp


9. Three phase motor code (NEMA)

HPCode
<1 HPL
1.5 to 2.0 HPL,M
3 HPK
5 HPJ
7 to 10 HPH
>15 HPG

10. Service factor of motor

HPSynchronous Speed (RPM)
3600 RPM1800 RPM1200 RPM900 RPM720 RPM600 RPM514 RPM
1 HP1.251.151.151.15111
1.5 to 1.25 HP1.151.151.151.151.151.15>1.15
150 HP1.151.151.151.151.151.151
200 HP1.151.151.151.151.1511
> 200 HP11.1511111


11. Type of contactor

TypeApplication
AC1Non Inductive Load or Slightly Inductive Load
AC2Slip Ring Motor, Starting, Switching OFF
AC3Squirrel Cage Motor
AC4,AC5,AC5a, AC5b,AC6aRapid Start & Rapid Stop
AC 5aAuxiliary Control circuit
AC 5bElectrical discharge Lamp
AC 6aElectrical Incandescent Lamp
AC 6bTransformer Switching
AC 7aSwitching of Capacitor Bank
AC 7bSlightly Inductive Load in Household
AC 5aMotor Load in Household
AC 8aHermetic refrigerant compressor motor with Manual Reset O/L  Relay
AC 8bHermetic refrigerant compressor motor with Automatic Reset O/L  Relay
AC 12Control of Resistive Load & Solid State Load
AC 13Control of Resistive Load & Solid State Load with Transformer Isolation
AC 14Control of small Electro Magnetic Load (<72 VA)
AC 15Control of Electro Magnetic Load (>72 VA)


12. Contactor coil

Coil VoltageSuffix
24 VoltT
48 VoltW
110 to 127 VoltA
220 to 240 VoltB
277 VoltH
380 to 415 VoltL

3 comments:

  1. It gives us more power when we visit this blog every time thanks lot
    May GOD be with you ever to help all like this
    With regards
    TNEB KATHIR

    ReplyDelete
  2. help me to culculate the how many earthpits required for a building with 1000A circuit breaker as incoming

    ReplyDelete