Search

Premium Membership

Get access to premium HV/MV/LV electrical guides, technical articles, research studies and much more.
Home / Technical Articles / Electrical Thumb Rules You MUST Follow (4)
Electrical Thumb Rules You MUST Follow - part 4
Electrical Thumb Rules You MUST Follow – part 4 (on photo: Distribution substation bus on a clear night in February by Eli Nelson, via Flickr)

Continued from: Electrical Thumb Rules You MUST Follow (Part 3)


Eight rules to follow:

  1. Substation Capacity and Short Circuit Current Capacity (As per GERC)
  2. Substation Capacity and Short Circuit Current Capacity (As per Central Electricity Authority)
  3. Minimum Ground Clearance and Fault Clearing Time
  4. Busbar Ampere Rating
  5. Busbar Spacing
  6. Sound Level of Diesel Generator (ANSI 89.2 and NEMA 51.20)
  7. IR Value of Transformer
  8. Standard Size of MCB, MCCB, ELCB, RCCB, SFU and Fuse

1. Substation Capacity and 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)

Go back to Rules ↑


2. Substation Capacity and 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

Go back to Rules ↑


3. 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

Go back to Rules ↑


4. Busbar Ampere Rating

For Phase Busbar Aluminium 130 Amp / Sq.cm or 800Amp / Sq.inch.
For Phase Busbar Copper 160 Amp / Sq.cm or 1000Amp / Sq.inch
For Neutral Busbar Same as Phase Busbar up to 200 Amp than Size of Neutral Busbar is at least half of Phase Busbar.

Go back to Rules ↑


5. Busbar Spacing

Between Phase and Earth 26mm (Min)
Between Phase and Phase 32mm (Min)
Busbar Support between Two Insulator 250mm.

Go back to Rules ↑


6. Sound Level of Diesel Generator (ANSI 89.2 and 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

Go back to Rules ↑


7. 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

Go back to Rules ↑


8. Standard Size of MCB, MCCB, ELCB, RCCB, SFU and Fuse

MCB, MCCB, ELCB, RCCB, SFU, Fuse – Standard Ratings
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

Premium Membership

Premium membership gives you an access to specialized technical articles and extra premium content (electrical guides and software).
Get Premium Now ⚡
author-pic

Jignesh Parmar

Jignesh Parmar has completed M.Tech (Power System Control), B.E (Electrical). He is member of Institution of Engineers (MIE), India. He has more than 13 years experience in transmission & distribution-energy theft detection and maintenance electrical projects.

13 Comments


  1. Praveen Kumar Yadav
    Aug 25, 2018

    What is Maximum sound level for
    1000 KVA and 1250 KVA DG Set’s


  2. NITIN
    Apr 19, 2018

    I want to install a bus bar. For total 6 rooms having 6 electric water gyser of 25 litres (2000 watt) and lighting.
    Which bus bar suits me.
    63 amp
    100 amp


  3. hari haran GKM
    Nov 21, 2017

    MCB/MCCB/ELCB Termination Wire / Cable
    MCCB Max. 25 Sq.mm is it correct??


  4. Ghazanfar Ali Khan
    Nov 11, 2017

    How the maximum voltage is specified for 132-KV and 220-KV for Lightning arresters ?
    How Tertiary winding a transformer mitigate third harmonics? This question is pending since Feb.2015 to answer.


  5. uday desai
    Oct 23, 2015

    Excellent information, which will usefull in daily working.


  6. Joseph Auo
    Jul 08, 2015

    Dear Sir,

    the minimum Ground clearances to Ground for the voltages 11kV to 132kV seem to be too small. They should be 5.6 for 11kV and 22kV and 6.5 for 33kV and 6.7 for 66kV and 132kV. The condition should be @ he maximum operating temperature of 75 Deg. C.


  7. Y M Yacoob
    Jun 19, 2015

    Sorry Jignesh, I just found all the past copies, Thanks


  8. Y M Yacoob
    Jun 19, 2015

    Hello Jignesh, thank you for the very interesting info. Where can I find parts 1 ; 2 & 3 ?


  9. anuja
    Feb 20, 2015

    Its too useful n knowledgeable thanku


  10. bavya
    Dec 04, 2014

    You are a motivation for many of unsuccessful electrical engineers


  11. Manoj Badave
    Jun 02, 2014

    Hello dear,
    you have a grand collection of information, very useful one for the freshers as well as for practicing engineers


  12. hoss
    Mar 22, 2014

    Hi mr. Parmar.Please send to me your experiences via my email hosseinke@yahoo.com.Best regards.


  13. merksab
    Dec 01, 2013

    Excelleng

Leave a Comment

Tell us what you're thinking... we care about your opinion!