Electrical Thumb rules

Special Thanks to http://electrical-engineering-portal.com/

Electrical Thumb Rules-(Part 1).

Cable Capacity:

For Cu Wire Current Capacity (Up to 30 Sq.mm) = 6X Size of Wire in Sq.mm

Ex. For 2.5 Sq.mm=6×2.5=15 Amp, For 1 Sq.mm=6×1=6 Amp, For 1.5 Sq.mm=6×1.5=9 Amp

For Cable Current Capacity = 4X Size of Cable in Sq.mm ,Ex. For 2.5 Sq.mm=4×2.5=9 Amp.

Nomenclature for cable Rating = Uo/U

where Uo=Phase-Ground Voltage, U=Phase-Phase Voltage, Um=Highest Permissible Voltage

Current Capacity of Equipments:

1 Phase Motor draws Current=7Amp per HP.

3 Phase Motor draws Current=1.25Amp per HP.

Full Load Current of 3 Phase Motor=HPx1.5

Full Load Current of 1 Phase Motor=HPx6

No Load Current of 3 Phase Motor =30% of FLC

KW Rating of Motor=HPx0.75

Full Load Current of equipment =1.39xKVA (for 3 Phase 415Volt)

Full Load Current of equipment =1.74xKw (for 3 Phase 415Volt)

Earthing Resistance:

Earthing Resistance for Single Pit=5Ω ,Earthing Grid=0.5Ω

As per NEC 1985 Earthing Resistance should be <5Ω.

Voltage between Neutral and Earth <=2 Volts

Resistance between Neutral and Earth <=1Ω

Creepage Distance=18 to 22mm/KV (Moderate Polluted Air) or

Creepage Distance=25 to 33mm/KV (Highly Polluted Air)

Minimum Bending Radius:

Minimum Bending Radius for LT Power Cable=12xDia of Cable.

Minimum Bending Radius for HT Power Cable=20xDia of Cable.

Minimum Bending Radius for Control Cable=10xDia of Cable.

Insulation Resistance:

Insulation Resistance Value for Rotating Machine= (KV+1) MΩ.

Insulation Resistance Value for Motor (IS 732) = ((20xVoltage (L-L)) / (1000+ (2xKW)).

Insulation Resistance Value for Equipment (<1KV) = Minimum 1 MΩ.

Insulation Resistance Value for Equipment (>1KV) = KV 1 MΩ per 1KV.

Insulation Resistance Value for Panel = 2 x KV rating of the panel.

Min Insulation Resistance Value (Domestic) = 50 MΩ / No of Points. (All Electrical Points with Electrical fitting & Plugs). Should be less than 0.5 MΩ

Min Insulation Resistance Value (Commercial) = 100 MΩ / No of Points. (All Electrical Points without fitting & Plugs).Should be less than 0.5 MΩ.

Test Voltage (A.C) for Meggering = (2X Name Plate Voltage) +1000

Test Voltage (D.C) for Meggering = (2X Name Plate Voltage).

Submersible Pump Take 0.4 KWH of extra Energy at 1 meter drop of Water.

Lighting Arrestor:

Arrestor have Two Rating=

(1) MCOV=Max. Continuous Line to Ground Operating Voltage.

(2) Duty Cycle Voltage. (Duty Cycle Voltage>MCOV).

Transformer:

Current Rating of Transformer=KVAx1.4

Short Circuit Current of T.C /Generator= Current Rating / % Impedance

No Load Current of Transformer=<2% of Transformer Rated current

Capacitor Current (Ic)=KVAR / 1.732xVolt (Phase-Phase)

Typically the local utility provides transformers rated up to 500kVA For maximum connected load of 99kW,

Typically the local utility provides transformers rated up to 1250kVA For maximum connected load of 150kW.


The diversity they would apply to apartments is around 60%

Maximum HT (11kV) connected load will be around 4.5MVA per circuit.

4No. earth pits per transformer (2No. for body and 2No. for neutral earthing),

Clearances, approx.1000mm around TC allow for transformer movement for replacement.

Diesel Generator:

Diesel Generator Set Produces=3.87 Units (KWH) in 1 Litter of Diesel.

Requirement Area of Diesel Generator = for 25KW to 48KW=56 Sq.meter, 100KW=65 Sq.meter.

DG less than or equal to 1000kVA must be in a canopy.

DG greater 1000kVA can either be in a canopy or skid mounted in an acoustically treated room DG noise levels to be less than 75dBA @ 1meter.

DG fuel storage tanks should be a maximum of 990 Litter per unit Storage tanks above this level will trigger more stringent explosion protection provision.

Current Transformer:

Nomenclature of CT:

Ratio: input / output current ratio

Burden (VA): total burden including pilot wires. (2.5, 5, 10, 15 and 30VA.)

Class: Accuracy required for operation (Metering: 0.2, 0.5, 1 or 3, Protection: 5, 10, 15, 20, 30).

Accuracy Limit Factor:

Nomenclature of CT: Ratio, VA Burden, Accuracy Class, Accuracy Limit Factor.Example: 1600/5, 15VA 5P10 (Ratio: 1600/5, Burden: 15VA, Accuracy Class: 5P, ALF: 10)

As per IEEE Metering CT: 0.3B0.1 rated Metering CT is accurate to 0.3 percent if the connected secondary burden if impedance does not exceed 0.1 ohms.

As per IEEE Relaying (Protection) CT: 2.5C100 Relaying CT is accurate within 2.5 percent if the secondary burden is less than 1.0 ohm (100 volts/100A).


Quick Electrical Calculation

1HP=0.746KW

Star Connection

1KW=1.36HP

Line Voltage=√3 Phase Voltage

1Watt=0.846 Kla/Hr

Line Current=Phase Current

1Watt=3.41 BTU/Hr

Delta Connection

1KWH=3.6 MJ

Line Voltage=Phase Voltage

1Cal=4.186 J

Line Current=√3 Phase Current

1Tone= 3530 BTU

85 Sq.ft Floor Area=1200 BTU

1Kcal=4186 Joule

1KWH=860 Kcal

1Cal=4.183 Joule

Electrical Thumb Rules (Part-2)

Useful Equations:

For Sinusoidal Current : Form Factor = RMS Value/Average Value=1.11

For Sinusoidal Current : Peak Factor = Max Value/RMS Value =1.414

Average Value of Sinusoidal Current(Iav)=0.637xIm (Im= Max.Value)

RMS Value of Sinusoidal Current(Irms)=0.707xIm (Im= Max.Value)

A.C Current=D.C Current/0.636.

Phase Difference between Phase= 360/ No of Phase (1 Phase=230/1=360°,2Phase=360/2=180°)

Short Circuit Level of Cable in KA (Isc)=(0.094xCable Dia in Sq.mm)/√ Short Circuit Time (Sec)

Max.Cross Section Area of Earthing Strip(mm2) =√(Fault Current x Fault Current x Operating Time of Disconnected Device ) / K

K=Material Factor, K for Cu=159, K for Alu=105, K for steel=58 , K for GI=80

Most Economical Voltage at given Distance=5.5x√ ((km/1.6)+(kw/100))

Cable Voltage Drop(%)=(1.732xcurrentx(RcosǾ+jsinǾ)x1.732xLength (km)x100)/(Volt(L-L)x Cable Run.

Spacing of Conductor in Transmission Line (mm) = 500 + 18x (P-P Volt) + (2x (Span in Length)/50).

Protection radius of Lighting Arrestor = √hx (2D-h) + (2D+L). Where h= height of L.A, D-distance of equipment (20, 40, 60 Meter), L=Vxt (V=1m/ms, t=Discharge Time).
Size of Lighting Arrestor= 1.5x Phase to Earth Voltage or 1.5x (System Voltage/1.732).

Maximum Voltage of the System= 1.1xRated Voltage (Ex. 66KV=1.1×66=72.6KV)

Load Factor=Average Power/Peak Power

If Load Factor is 1 or 100% = This is best situation for System and Consumer both.

If Load Factor is Low (0 or 25%) =you are paying maximum amount of KWH consumption. Load Factor may be increased by switching or use of your Electrical Application.

Demand Factor= Maximum Demand / Total Connected Load (Demand Factor <1)

Demand factor should be applied for Group Load

Diversity Factor= Sum of Maximum Power Demand / Maximum Demand (Demand Factor >1)

Diversity factor should be consider for individual Load

Plant Factor(Plant Capacity)= Average Load / Capacity of Plant

Fusing Factor=Minimum Fusing Current / Current Rating (Fusing Factor>1).

Voltage Variation(1 to 1.5%)= ((Average Voltage-Min Voltage)x100)/Average Voltage

Ex: 462V, 463V, 455V, Voltage Variation= ((460-455) x100)/455=1.1%.

Current Variation(10%)= ((Average Current-Min Current)x100)/Average Current

Ex:30A,35A,30A, Current Variation=((35-31.7)x100)/31.7=10.4%

Fault Level at TC Secondary=TC (VA) x100 / Transformer Secondary (V) x Impedance (%)

Motor Full Load Current= Kw /1.732xKVxP.FxEfficiency

Electrical Thumb Rules-(Part-3)

Size of Capacitor for P.F Correction:

For Motor

Size of Capacitor = 1/3 Hp of Motor ( 0.12x KW of Motor)

For Transformer

< 315 KVA

5% of KVA Rating

315 KVA to 1000 KVA

6% of KVA Rating

>1000 KVA

8% of KVA Rating

Earthing Resistance value:

Power Station

0.5 Ω

Sub Station Major

1.0 Ω

Sub Station Minor

2.0 Ω

Distribution Transformer

5.0 Ω

Transmission Line

10 Ω

Single Isolate Earth Pit

5.0 Ω

Earthing Grid

0.5 Ω

As per NEC Earthing Resistance should be <5.0 Ω

Voltage Limit (As per CPWD & Kerala Elect.Board):

Voltage Limit (As Per CPWD)

240V
< 5 KW

415V
<100 KVA

11KV
<3  MVA

22KV
<6 MVA


33KV
<12 MVA


66KV
<20 MVA


110KV
<40 MVA

220KV
>40 MVA

Voltage Variation

> 33 KV
(-) 12.5% to (+) 10%

< 33 KV
(-) 9% to (+) 6%

Low Voltage
(-) 6% to (+) 6%

Insulation Class:

Insulation
Temperature

Class A
105°C

Class E
120°C

Class B
130°C

Class F
155°C

Class H
180°C

Class N
200°C

Standard Voltage Limit:

Voltage
IEC (60038)
IEC (6100:3.6)
Indian Elect. Rule

ELV
< 50 V

LV
50 V to 1 KV
<=1 KV
< 250 V

MV

<= 35 KV
250 V to 650 V

HV
> 1KV
<= 230 KV
650 V to 33 KV

EHV

> 230 KV
> 33 KV

Standard Electrical Connection (As per GERC):

As per Type of Connection

Connection

Voltage

LT Connection

<=440V

HT connection

440V to 66KV







EHT connection

>= 66KV





As per Electrical Load Demand





Up 6W Load demand

1 Phase 230V Supply





6W to 100KVA(100KW)

3 Phase 440V Supply





100KVA to 2500KVA

11KV,22KV,33KV





Above 2500KVA

66KV





HT Connection Earthing





H.T Connection’s Earthing Strip

20mmX4mm Cu. Strip





CT & PT bodies

2Nos





PT Secondary

1Nos





CT Secondary

1Nos





I/C and O/G Cable+ Cubicle Body

2Nos






Standard Meter Room Size (As per GERC):


Meter Box Height
Upper level does not beyond 1.7 meter and Lower level should not


below 1.2 meter from ground.




Facing of Meter Box
Meter Box should be at front area of Building at Ground Floor.




Meter Room / Closed Shade
4 meter square Size





Approximate Load as per Sq.ft Area (As per DHBVN):


Sq.ft Area
Required Load (Connected)




< 900 Sq.ft
8 KW




901 Sq.ft to 1600 Sq.ft
16 KW




1601 Sq.ft to 2500 Sq.ft
20 KW




> 2500 Sq.ft
24 KW




For Flats :100 Sq.ft / 1 KW





For Flats USS /TC: 100 Sq.ft / 23 KVA






Contracted Load in case of High-rise Building:


For Domestic Load
500 watt per 100 Sq. foot of the constructed area.




For Commercial
1500 watt per 100 Sq. foot of the constructed area





For lift, water lifting pump, streetlight if any, corridor/campus

Other Common Load
lighting and other common facilities, actual load shall be


calculated






Staircase Light

11KW/Flat Ex: 200Flat=200×11=2.2KW






Sanctioned Load for Building





Up to 50 Kw

The L.T. existing mains shall be strengthened.





50 kW to 450 kW (500 kVA)

11 kV existing feeders shall be extended if spare capacity is



available otherwise, new 11 kV feeders shall be constructed.





450 kW to 2550 kW (3000 kVA)

11 kV feeder shall be constructed from the nearest 33 kV or 110



kV substation





2550 kW to 8500 kW (10,000 kVA)

33kV feeder from 33 kV or 110 kV sub station





8500 kW (10,000 kVA)

110 kV feeder from nearest 110 kV or 220 kV sub-station












Electrical Thumb Rules-(Part-4)


AUGUST 18, 2013 5 COMMENTS

Sub Station Capacity & Short Circuit Current Capacity:




As per GERC






Voltage
Sub Station Capacity

Short Circuit Current






400 KV
Up to 1000 MVA

40 KA  (1 to 3 Sec)






220 KV
Up to 320 MVA

40 KA  (1 to 3 Sec)






132 KV
Up to 150 MVA

32 KA  (1 to 3 Sec)






66 KV
Up to 80 MVA

25 KA  (1 to 3 Sec)






33 KV
1.5 MVA to 5 MVA

35 KA (Urban) (1 to 3 Sec)






11 KV
150 KVA to 1.5 MVA

25 KA (Rural) (1 to 3 Sec)






415 V
6 KVA to 150 KVA

10 KA  (1 to 3 Sec)






220 V
Up to 6 KVA

6 KA (1 to 3 Sec)







Sub Station Capacity & Short Circuit Current Capacity:


As per Central Electricity Authority

Voltage
Sub Station Capacity
Short Circuit Current





765 KV
4500 MVA
31.5 KA for 1 Sec





400 KV
1500 MVA
31.5 KA for 1 Sec





220 KV
500 MVA
40 KA for 1 Sec





110/132 KV
150 MVA
40 KA or 50 KA for 1 Sec





66 KV
75 MVA
40 KA or 50 KA for 1 Sec






Minimum Ground Clearance and Fault Clearing Time:


Voltage
Min. Ground Clearance
Fault Clear Time





400 KV
8.8 Meter
100 mille second








220 KV

8.0 Meter


120 mille second













132 KV

6.1 Meter


160 mille second













66 KV

5.1 Meter


300 mille second













33 KV

3.7 Meter
















11 KV

2.7 Meter














Bus bar Ampere Rating:





















For Phase Bus bar


Aluminium 130 Amp / Sq.cm or 800Amp / Sq.inch.











For Phase Bus bar


Copper 160 Amp / Sq.cm or 1000Amp / Sq.inch










For Neutral Bus bar

Same as Phase Bus bar up to 200 Amp than Size of Neutral Bus bar is at







least half of Phase Bus bar.













Bus bar Spacing:













Between Phase and Earth


26mm (Min)










Between Phase and Phase


32mm (Min)









Bus bar Support between Two Insulator

250mm.













Sound Level of Diesel Generator (ANSI 89.2&NEMA 51.20):


KVA
Max. Sound Level




<9 KVA
40 DB




10 KVA to 50 KVA
45 DB




51 KVA to 150 KVA
50 DB




151 KVA to 300 KVA
55 DB




301 KVA to 500 KVA
60 DB




IR Value of Transformer:




IR Value of Transformer

Voltage
30°C
40°C
50°C






>66KV
600MΩ
300MΩ
150MΩ






22KV to 33KV
500MΩ
250MΩ
125MΩ






6.6KV to 11KV
400MΩ
200MΩ
100MΩ






<6.6KV
200MΩ
100MΩ
50MΩ






415V
100MΩ
50MΩ
20MΩ







Standard Size of MCB/MCCB/ELCB/RCCB/SFU/Fuse:



MCB Up to 63 Amp (80Amp and 100 Amp a per Request)


MCCB

Up to 1600 Amp (2000 Amp as per Request)





ACB

Above 1000 Amp





MCB Rating

6A,10A,16A,20A,32A,40A,50A,63A





MCCB Rating

0.5A,1A,2A,4A,6A,10A,16A,20A,32A,40A,50A,63A,80A,100A



(Domestic Max 6A)





RCCB/ELCB

6A,10A,16A,20A,32A,40A,50A,63A,80A,100A





Sen. of ELCB

30ma (Domestic),100ma (Industrial),300ma





DPIC (Double Pole Iron Clad)

5A,15A,30 A for 250V

main switch







TPIC (Triple Pole Iron Clad)

30A, 60A, 100A, 200 A For 500 V

main switch







DPMCB

5A, 10A, 16A, 32A and 63 A for 250V





TPMCCB

100A,200A, 300Aand 500 A For 660 V





TPN main switch

30A, 60A, 100A, 200A, 300 A For 500 V





TPNMCB

16A, 32A,63A For 500 V, beyond this TPNMCCB: 100A, 200A,



300A, 500 A For 660 V





TPN Fuse Unit (Rewirable)

16A,32A,63A,100A,200A





Change over switch (Off

32A,63A,100A,200A,300A,400A,630A,800A

Load)







SFU (Switch Fuse Unit)

32A,63A,100A,125A,160A,200A,250A,315A,400A,630A





HRC Fuse TPN (Bakelite)

125A,160A,200A,250A,400A.630A





HRC Fuse DPN (Bakelite)

16A,32A,63A






MCB/MCCB/ELCB Termination Wire / Cable





Up to 20A MCB

Max. 25 Sq.mm





20A to 63A MCB

Max. 35 Sq.mm





MCCB

Max. 25 Sq.mm





6A to 45A ELCB

16 Sq.mm





24A to 63A ELCB

35 Sq.mm





80A to 100A ELCB

50 Sq.mm









Electrical Thumb Rules-(Part-5)



SEPTEMBER 1, 2013 4 COMMENTS

Standard Size of Transformer (IEEE/ANSI 57.120):


Single Phase Transformer
Three Phase Transformer




5KVA,10 KVA,15 KVA,25 KVA,37.5
3 KVA,5 KVA,9 KVA,15 KVA,30 KVA,45 KVA,75

KVA,50 KVA,75 KVA,100 KVA,167
KVA,112.5 KVA,150 KVA,225 KVA,300 KVA,500 KVA,750

KVA,250 KVA,
KVA,1MVA,1.5 MVA,2 MVA,2.5 MVA,3.7 MVA,5

333 KVA,500 KVA,833 KVA,1.25
MVA,7.5MVA, 10MVA ,12MVA,15MVA,20MVA ,25MVA,

KVA,1.66 KVA,2.5 KVA,3.33 KVA,5.0
30MVA,37.5MVA ,50MVA ,60MVA,75MVA,100MVA

KVA,6.6 KVA,8.3 KVA,10.0 KVA,12.5


KVA,16.6 KVA,20.8 KVA,25.0


KVA,33.33 KVA






Standard Size of Motor (HP):


Electrical Motor (HP)


1,1.5,2,3,5,7.5,10,15,20,30,40,50,60,75,100,125,150,200,250,300,400,450,500,600,700,

800,900,1000,1250,1250,1500,1750,2000,2250,3000,3500,4000


Approximate RPM of Motor


HP
RPM




< 10 HP
750 RPM




10 HP to 30 HP
600 RPM




30 HP to 125 HP
500 RPM




125 HP to 300 HP
375 RPM




Standard Size of Motor (HP):




Electrical Motor (HP)


1,1.5,2,3,5,7.5,10,15,20,30,40,50,60,75,100,125,150,200,250,300,400,450,500,600,700,

800,900,1000,1250,1250,1500,1750,2000,2250,3000,3500,4000


Motor Line Voltage:


Motor (KW)
Line Voltage




< 250 KW
440 V (LV)




150 KW to 3000KW
2.5 KV to 4.1 KV (HV)




200 KW to 3000KW
3.3 KV to 7.2 KV (HV)




1000 KW to 1500KW
6.6 KV to 13.8 KV (HV)




Motor Starting Current:




Supply

Size of Motor
Max. Starting Current





1 Phase
< 1 HP
6 X Motor Full Load Current





1 Phase
1 HP to 10 HP
3 X Motor Full Load Current






3 Phase
10
HP
2 X Motor Full Load Current






3 Phase
10
HP to 15 HP
2 X Motor Full Load Current





3 Phase
> 15 HP
1.5 X Motor Full Load Current









Motor Starter:


Starter
HP or KW
Starting Current
Torque






DOL
<13 HP(11KW)
7 X Full Load Current
Good






Star-
13 HP to 48 HP
3 X Full Load Current
Poor

Delta









Auto TC
> 48 HP (37 KW)
4 X Full Load Current
Good/ Average






VSD

0.5 to 1.5 X Full Load Current
Excellent








Motor > 2.2KW Should not connect direct to supply voltage if it is in Delta winding


Impedance of Transformer (As per IS 2026):


MVA
% Impedance




< 1 MVA
5%




1 MVA to 2.5 MVA
6%




2.5 MVA to 5 MVA
7%




5 MVA to 7 MVA
8%




7 MVA to 12 MVA
9%




12 MVA to 30 MVA
10%




> 30 MVA
12.5%




Standard Size of Transformer:




Standard Size of Transformer
KVA




Power Transformer (Urban)
3,6,8,10,16




Power Transformer (Rural)
1,1.6,3.15,5




Distribution Transformer
25,50,63,100,250,315,400,500,630










Electrical Thumb Rules-(Part-6)


SEPTEMBER 5, 2013 9 COMMENTS

Transformer Earthing Wire / Strip Size:


Size of T.C or DG
Body Earthing
Neutral Earthing





<315 KVA
25×3 mm Cu / 40×6 mm GI Strip
25×3 mm Cu Strip





315 KVA to 500 KVA
25×3 mm Cu / 40×6 mm GI Strip
25×3 mm Cu Strip





500 KVA to 750 KVA
25×3 mm Cu / 40×6 mm GI Strip
40×3 mm Cu Strip





750 KVA to 1000 KVA
25×3 mm Cu / 40×6 mm GI Strip
50×3 mm Cu Strip






Motor Earthing Wire / Strip Size:

Size of Motor
Body Earthing




< 5.5 KW
85 SWG GI Wire




5.5 KW to 22 KW
25×6 mm GI Strip




22 KW to 55 KW
40×6 mm GI Strip







>55 KW

50×6 mm GI Strip









Panel Earthing Wire / Strip Size:









Type of Panel

Body Earthing









Lighting & Local Panel

25×6 mm GI Strip









Control & Relay Panel

25×6 mm GI Strip









D.G & Exciter Panel

50×6 mm GI Strip









D.G & T/C Neutral

50×6 mm Cu Strip









Electrical Equipment Earthing:















Equipment

Body Earthing









LA (5KA,9KA)

25×3 mm Cu Strip









HT Switchgear

50×6 mm GI Strip









Structure

50×6 mm GI Strip









Cable Tray

50×6 mm GI Strip









Fence / Rail Gate

50×6 mm GI Strip









Earthing Wire (As per BS 7671)









Cross Section Area of Phase, Neutral

Minimum Cross Section area of Earthing Conductor



Conductor(S) mm2

(mm2)









S<=16

S (Not less than 2.5 mm2)









16<S<=35

16









S>35

S/2









Area for Transformer Room: (As per NBC-2005):


Transformer
Min. Transformer
Min. Total Sub Station Area(
Min. Space

Size
Room Area (M2)
Incoming HV,LV Panel, T.C
Width (Meter)



Roof) (M2)







1X160
14
90
9






2X160
28
118
13.5






1X250
15
91
9






2X250
30
121
13.5






1X400
16.5
93
9






2X400
33
125
13.5






3X400
49.5
167
18






2X500
36
130
14.5






3X500
54
172
19






2X630
36
132
14.5






3X630
54
176
19






2X800
39
135
14.5








3X800
58
181
14






2X1000
39
149
14.5






3X1000
58
197
19


















The Capacitor Bank should be automatic Switched type for Sub Station of 5MVA and Higher.

Transformer up to 25KVA can be mounted direct on Pole.

Transformer from 25KVA to 250KVA can be mounted either on “H” Frame of Plinth.

Transformer above 250KVA can be mounted Plinth only.

Transformer above 100MVA shall be protected by Drop out Fuse or Circuit Breaker.

Span of Transmission Line (Central Electricity Authority):


Voltage
Normal Span




765 KV
400 to 450 Meter




400 KV
400 Meter




220 KV
335,350,375 Meter




132 KV
315,325,335 Meter




66 KV
240,250,275 Meter





Max. Lock Rotor Amp for 1 Phase 230 V Motor (NEMA)


HP
Amp




1 HP
45 Amp




1.5 HP
50 Amp




2 HP
65 Amp




3 HP
90 Amp




5 HP
135 Amp




7.5 HP
200 Amp




10 HP
260 Amp





Three Phase Motor Code (NEMA)




HP




Code

















<1 HP




L

















1.5 to 2.0 HP




L,M

















3 HP




K

















5 HP




J















7 to 10 HPPHPHPHHHHH



H

















>15 HP




G













Service Factor of Motor:























Synchronous Speed (RPM)



HP













3600

1800
1200
900
720
600
514














RPM

RPM
RPM
RPM
RPM
RPM
RPM












1 HP

1.25

1.15
1.15
1.15
1
1
1












1.5 to 1.25
1.15

1.15
1.15
1.15
1.15
1.15
1.15

HP




































150 HP
1.15
1.15
1.15
1.15
1.15
1.15
1










200 HP
1.15
1.15
1.15
1.15
1.15
1
1










> 200 HP
1
1.15
1
1
1
1
1











Type of Contactor:


Type
Application




AC1
Non Inductive Load or Slightly Inductive Load




AC2
Slip Ring Motor, Starting, Switching OFF




AC3
Squirrel Cage Motor




AC4,AC5,AC5a,
Rapid Start & Rapid Stop

AC5b,AC6a





AC 5a
Auxiliary Control circuit




AC 5b
Electrical discharge Lamp




AC 6a
Electrical Incandescent Lamp




AC 6b
Transformer Switching




AC 7a
Switching of Capacitor Bank




AC 7b
Slightly Inductive Load in Household




AC 5a
Motor Load in Household




AC 8a
Hermetic refrigerant compressor motor with Manual Reset O/L  Relay




AC 8b
Hermetic refrigerant compressor motor with Automatic Reset O/L  Relay




AC 12
Control of Resistive Load & Solid State Load




AC 13
Control of Resistive Load & Solid State Load with Transformer Isolation




AC 14
Control of small Electro Magnetic Load (<72 VA)




AC 15
Control of Electro Magnetic Load (>72 VA)




Contactor Coil:




Coil Voltage
Suffix




24 Volt
T




48 Volt
W




110 to 127 Volt
A




220 to 240 Volt
B




277 Volt
H




380 to 415 Volt
L







Electrical Thumb Rules-(Part-7)

SEPTEMBER 16, 2013 7 COMMENTS


Overhead Conductor /Cable Size:


Voltage

KV

KV

LT

Overhead Conductor
Cable Size

ACSR-Panther/Wolf/Dog , AAAC
150,185,300,400,240 mm2 Cable

ACSR-Dog/Recon/Rabbit , AAAC
120, 150,185,300 mm2 Cable

ACSR-Dog/Recon/Rabbit , AAC,AAAC
95,120, 150,185,300 mm2 Cable




Transmission / Distribution Line:



Span

400KV=400 Meter

220KV=350 Meter

132KV=335 Meter

66KV=210 Meter

Conductor Ampere

Dog=300Amp

Panther=514Amp

Zebra=720Amp

Rabbit=208Amp

Moose=218Amp

Height of Tower

400KV=30Meter (Base 8.8 Meter)

220KV=23Meter (Base 5.2 Meter)

220KV Double Circuit=28 Meter


66KV=13Meter


Voltage wise Conductor


400KV=Moose ACSR=500MVA Load


220KV=Zebra ACSR=200MVA Load


132KV=Panther ACSR=75MVA Load


66KV=Dog ACSR=50MVA Load



Type of Tower:



Type


A

B

C

D


Used
Angle/Deviation

Suspension Tower
Up to 2°

Small Angle Tower
2° to 15°

Medium Angle Tower
15° to 30°

Large Angle / Dead End Tower
30° to 60° & Dead End




Tower Swing Angle Clearance (Metal Part to Live Part):


Swing Angle

Live Part to Metal Part Clearance (mm)



66KV
132KV
220KV

400KV

0°
915mm
1530mm
2130mm

3050mm

15°
915mm
1530mm
2130mm

-

22°
-
-
-

3050mm

30°
760mm
1370mm
1830mm

-

44°
-
-
-

1860mm

44°
610mm
1220mm
1675mm

-



Cable Coding (IS 1554)  A2XFY / FRLS / FRPVC / FRLA / PILC)


A Aluminium

2X XLPE


Flat Armoured

WWire Armoured

YOuter PVC Insulation Sheath

WSteel Round Wire


WW
Steel double round wire Armoured

YY
Steel double Strip Armoured

FR
Fire Retardation

LS
Low Smoke

LA
Low Acid Gas Emission

WA
Non Magnetic round wire Armoured

FA
Non Magnetic Flat wire Armoured

FF
Double Steel Round Wire Armoured



Corona Ring Size:


Voltage
Size

<170 KV
160mm Ring put at HV end

>170 KV
350mm Ring put at HV end

>275 KV
450mm Ring put at HV end & 350 mm Ring put at Earth end


Load as per Sq.Ft:



Type of Load
Load/Sq.Ft

Industrial
1000 Watt/Sq.Ft

Commercial
30 Watt/Sq.Ft

Domestic
15 Watt/Sq.Ft

Lighting
15 Watt/Sq.Ft



Diversity Factor

0.5

0.8

0.4

0.8


Size of Ventilation Shaft:



Height of Building in meter
Size of ventilation shaft in sq meter




9.0
1.5

12.5
3.0

15 and above
4.0



Minimum size of shaft in meter


1.0


1.2


1.5




Electrical Thumb Rules-(Part-8)


OCTOBER 1, 2013 6 COMMENTS

Accuracy Class of Metering CT:





Metering Class CT






Class

Applications






0.1 To

Precision measurements

0.2









0.5

High grade kilowatt hour meters for commercial grade kilowatt hour meters






3

General industrial measurements






3 OR 5

Approximate measurements






Accuracy Class Letter of CT:









Metering Class CT





Accuracy Class

Applications








B
Metering Purpose





Protection Class CT




C
CT has low leakage flux.




T
CT can have significant leakage flux.



CT accuracy is applicable within the entire range of secondary currents from 5 to 20 times the nominal CT rating. (Typically wound CTs.)


CT accuracy applies at the maximum rated secondary burden at 20 time rated only. The ratio accuracy can be up to four times greater than the listed value, depending on connected burden and fault current. (Typically window, busing, or bar-type CTs.)

Accuracy Class of Protection CT:


Class
Applications




10P5
Instantaneous over current relays & trip coils: 2.5VA




10P10
Thermal inverse time relays: 7.5VA




10P10
Low consumption Relay: 2.5VA




10P10/5
Inverse definite min. time relays (IDMT) over current




10P10
IDMT Earth fault relays with approximate time grading:15VA




5P10
IDMT Earth fault relays with phase fault stability or accurate time grading: 15VA