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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 CapacityShort Circuit Current
400 KVUp to 1000 MVA40 KA  (1 to 3 Sec)
220 KVUp to 320 MVA40 KA  (1 to 3 Sec)
132 KVUp to 150 MVA32 KA  (1 to 3 Sec)
66 KVUp to 80 MVA25 KA  (1 to 3 Sec)
33 KV1.5 MVA to 5 MVA35 KA (Urban) (1 to 3 Sec)
11 KV150 KVA to 1.5 MVA25 KA (Rural) (1 to 3 Sec)
415 V6  KVA to 150 KVA10 KA  (1 to 3 Sec)
220 VUp to 6 KVA6 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 CapacityShort Circuit Current
765 KV4500 MVA31.5 KA for 1 Sec
400 KV1500 MVA31.5 KA for 1 Sec
220 KV500 MVA40 KA for 1 Sec
110/132 KV150 MVA40 KA or 50 KA for 1 Sec
66 KV75 MVA40 KA or 50 KA for 1 Sec

Go back to Rules ↑


3. Minimum Ground Clearance and Fault Clearing Time

Voltage Min. Ground ClearanceFault Clear Time
400 KV8.8 Meter100 mille second
220 KV8.0 Meter120 mille second
132 KV6.1 Meter160 mille second
66 KV5.1 Meter300 mille second
33 KV3.7 Meter
11 KV2.7 Meter

Go back to Rules ↑


4. Busbar Ampere Rating

For Phase BusbarAluminium 130 Amp / Sq.cm or 800Amp / Sq.inch.
For Phase BusbarCopper 160 Amp / Sq.cm or 1000Amp / Sq.inch
For Neutral BusbarSame 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 Earth26mm (Min)
Between Phase and Phase32mm (Min)
Busbar Support between Two Insulator250mm.

Go back to Rules ↑

6. Sound Level of Diesel Generator (ANSI 89.2 and NEMA 51.20)

KVAMax. Sound Level
<9 KVA40 DB
10 KVA to 50 KVA45 DB
51 KVA to 150 KVA50 DB
151 KVA to 300 KVA55 DB
301 KVA to 500 KVA60 DB

Go back to Rules ↑


7. IR Value of Transformer

IR Value of Transformer
Voltage30°C40°C50°C
>66KV600MΩ300MΩ150MΩ
22KV to 33KV500MΩ250MΩ125MΩ
6.6KV to 11KV400MΩ200MΩ100MΩ
<6.6KV200MΩ100MΩ50MΩ
415V100MΩ50MΩ20MΩ

Go back to Rules ↑


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

MCB, MCCB, ELCB, RCCB, SFU, Fuse – Standard Ratings
MCBUp to 63 Amp (80Amp and 100 Amp a    per Request)
MCCBUp to 1600 Amp (2000 Amp as per Request)
ACBAbove 1000 Amp
MCB Rating6A,10A,16A,20A,32A,40A,50A,63A
MCCB Rating0.5A,1A,2A,4A,6A,10A,16A,20A,32A,40A,50A,63A,80A,100A (Domestic Max 6A)
RCCB/ELCB6A,10A,16A,20A,32A,40A,50A,63A,80A,100A
Sen. of ELCB30ma (Domestic),100ma (Industrial),300ma
DPIC (Double Pole Iron Clad) main switch5A,15A,30 A for 250V
TPIC (Triple Pole Iron Clad) main switch30A, 60A, 100A, 200 A For 500 V
DPMCB5A, 10A, 16A, 32A and 63 A for 250V
TPMCCB100A,200A, 300Aand 500 A For 660 V
TPN main switch30A, 60A, 100A, 200A, 300 A For 500 V
TPNMCB16A, 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 MCBMax. 25 Sq.mm
20A to 63A MCBMax. 35 Sq.mm
MCCBMax. 25 Sq.mm
6A to 45A ELCB16 Sq.mm
24A to 63A ELCB35 Sq.mm
80A to 100A ELCB50 Sq.mm

About Author //

author-pic

Jignesh Parmar

jiguparmar - Jignesh Parmar has completed M.Tech (Power System Control) ,B.E(Electrical). He is member of Institution of Engineers (MIE),India. Membership No:M-1473586.He has more than 13 years experience in Transmission -Distribution-Electrical Energy theft detection-Electrical Maintenance-Electrical Projects (Planning-Designing-Technical Review-coordination -Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He has published numbers of Technical Articles in "Electrical Mirror", "Electrical India", "Lighting India", "Industrial Electrix"(Australian Power Publications) Magazines. He is Freelancer Programmer of Advance Excel and design useful Excel base Electrical Programs as per IS, NEC, IEC,IEEE codes. 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 Comments


  1. uday desai
    Oct 23, 2015

    Excellent information, which will usefull in daily working.


  2. 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.


  3. Y M Yacoob
    Jun 19, 2015

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


  4. Y M Yacoob
    Jun 19, 2015

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


  5. anuja
    Feb 20, 2015

    Its too useful n knowledgeable thanku


  6. bavya
    Dec 04, 2014

    You are a motivation for many of unsuccessful electrical engineers


  7. 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


  8. hoss
    Mar 22, 2014

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


  9. merksab
    Dec 01, 2013

    Excelleng

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