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Home / Technical Articles / Electrical Thumb Rules You MUST Follow (7)
Electrical Thumb Rules You MUST Follow, part 7
Electrical Thumb Rules You MUST Follow, part 7 (photo by joy russell via Flickr)

Continued from: Electrical Thumb Rules You MUST Follow (Part 6)

8 electrical thumb rules to follow:

  1. Overhead conductor / cable size
  2. Transmission / distribution  line (span, height of tower)
  3. Types of towers
  4. Tower swing angle clearance (metal part to live part)
  5. Cable coding, IS 1554 (A2XFY, FRLS, FRPVC, FRLA, PILC)
  6. Corona ring size
  7. Load as per Sq.Ft
  8. Size of ventilation shaft

1. Overhead conductor / cable size

VoltageOverhead ConductorCable Size
33 KVACSR-Panther/Wolf/Dog , AAAC150,185,300,400,240 mm2 Cable
11 KVACSR-Dog/Recon/Rabbit , AAAC120, 150,185,300 mm2 Cable
LTACSR-Dog/Recon/Rabbit , AAC, AAAC95,120, 150,185,300 mm2 Cable

Go back to Rules ↑

2. Transmission / distribution line (span, tower height)

SpanHeight of Tower
400KV = 400 Meter400KV=30Meter (Base 8.8 Meter)
220KV = 350 Meter220KV=23Meter (Base 5.2 Meter)
132KV = 335 Meter220KV Double Circuit=28 Meter
66KV = 210 Meter66KV=13Meter
Conductor AmpereVoltage wise Conductor
Dog = 300Amp400KV=Moose ACSR=500MVA Load
Panther = 514Amp220KV=Zebra ACSR=200MVA Load
Zebra = 720Amp132KV=Panther ACSR=75MVA Load
Rabbit = 208Amp66KV=Dog ACSR=50MVA Load
Moose = 218Amp

Go back to Rules ↑

3. Types of Towers

ASuspension TowerUp to 2°
BSmall Angle Tower2° to 15°
CMedium Angle Tower15° to 30°
DLarge Angle / Dead End Tower30° to 60° & Dead End

Go back to Rules ↑

4. Tower Swing Angle Clearance (Metal Part to Live Part)

Swing AngleLive Part to Metal Part Clearance (mm)

Go back to Rules ↑

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

FFlat Armoured
WWire Armoured
YOuter PVC Insulation Sheath
WSteel Round Wire
WWSteel double round wire Armoured
YYSteel double Strip Armoured
FRFire Retardation
LSLow Smoke
LALow Acid Gas Emission
WANon Magnetic round wire Armoured
FANon Magnetic Flat wire Armoured
FFDouble Steel Round Wire Armoured

Go back to Rules ↑

6. Corona Ring Size

<170 KV160mm Ring put at HV end
>170 KV350mm Ring put at HV end
>275 KV450mm Ring put at HV end & 350 mm Ring put at Earth end

Go back to Rules ↑

7. Load as per Sq.Ft

Type of LoadLoad/Sq.FtDiversity Factor
Industrial1000 Watt/Sq.Ft0.5
Commercial30 Watt/Sq.Ft0.8
Domestic15 Watt/Sq.Ft0.4
Lighting15 Watt/Sq.Ft0.8

Go back to Rules ↑

8. Size of Ventilation Shaft

Height of Building in meterSize of ventilation shaft in sq meterMinimum size of shaft in meter
15 and above4.01.5

Go back to Rules ↑

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More Information

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 20 years experience in transmission & distribution-energy theft detection and maintenance electrical projects.


    Aug 22, 2014

    Dear sir,

    I want know how to select MCCB breaker with kA rating of the Load.



  2. Ahmed Al-Wajeeh
    Aug 21, 2014

    Dear Sir,
    We have in our transmission 400kV system high Corona losses
    I will appreciate if could provide me with any related information.

  3. manyamganesh
    Jun 16, 2014

    Sir i want knowcontrolling wiring iec codes for vaccum circuit breakers i.e ferrules code j means d.c voltage,k means controll signals and more can i get it

    Dec 25, 2013

    I want more information about LT-HT installation, testing, commissioning. And also a energy audit , green energy.

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