Electrical Thumb Rules-(Part-4)

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):


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









22KV to 33KV




6.6KV to 11KV












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) main switch 5A,15A,30 A for 250V
TPIC (Triple Pole Iron Clad) main switch 30A, 60A, 100A, 200 A For 500 V
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 Load) 32A,63A,100A,200A,300A,400A,630A,800A
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

About Jignesh.Parmar
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 13 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

9 Responses to Electrical Thumb Rules-(Part-4)

  1. tusharmahajan says:


  2. Maulesh Patel says:

    Dear Jigneshbhai,,

    Can you please guide me about the installation of Air terminal/Lightning arrester on the water tank roof…?

    Actually i am in little confusion in that because there is also internal cathodic protection for the tank. and if we directly fix that airterminal on tank roof without isolate it with the tank body/roof,then it will be affect to the internal cathodic protection of tank or not. Even though tank shell will be connected to the earthing also.


  3. Siddavatam Nizamuddin says:

    Very good information.

  4. kandage says:

    Good work keep it up

  5. nakul says:

    which standard you have taken here?

  6. how and why power factor improvement in electrical circute i want information in hindi language

  7. V.G SANTHOSH says:

    HI sir,

    I am having some doubts in measuring Insulation resistance.

    DOUBT 1:

    What is the difference between Measuring Insulation Resistance of a Motor/Generator using Megger and using Multimeter.

    Where to use Multimeter and where to use megger

    DOUBT 2:

    For what applications we have to use star connected Motor (PERMANENTLY IN STAR) and where to use Delta connected Motor (PERMANENTLY IN DELTA)

    DOUBT 3:

    This is about Pneumatics……….. in what way 4/2 valve is different from 5/2 valve i know a difference between them is 5/2 valve has one additional exhaust port. But both working Principles is same. is there is any other difference between these.

  8. suraj amatya says:

    want to know about XLPE HT and LT.

    maximum distance of ACSR can be used in LV line. Thumb rule for LV distribution ..

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