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

Voltage Overhead Conductor Cable Size
33 KV ACSR-Panther/Wolf/Dog , AAAC 150,185,300,400,240 mm2 Cable
11 KV ACSR-Dog/Recon/Rabbit , AAAC 120, 150,185,300 mm2 Cable
LT ACSR-Dog/Recon/Rabbit , AAC, AAAC 95,120, 150,185,300 mm2 Cable

Go back to Rules ↑

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

Span Height of Tower
400KV = 400 Meter 400KV=30Meter (Base 8.8 Meter)
220KV = 350 Meter 220KV=23Meter (Base 5.2 Meter)
132KV = 335 Meter 220KV Double Circuit=28 Meter
66KV = 210 Meter 66KV=13Meter
Conductor Ampere Voltage wise Conductor
Dog = 300Amp 400KV=Moose ACSR=500MVA Load
Panther = 514Amp 220KV=Zebra ACSR=200MVA Load
Zebra = 720Amp 132KV=Panther ACSR=75MVA Load
Rabbit = 208Amp 66KV=Dog ACSR=50MVA Load
Moose = 218Amp

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3. Types of Towers

Type Used Angle/Deviation
A Suspension Tower Up to 2°
B Small Angle Tower 2° to 15°
C Medium Angle Tower 15° to 30°
D Large Angle / Dead End Tower 30° to 60° & Dead End

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

Swing Angle Live Part to Metal Part Clearance (mm)
66KV 132KV 220KV 400KV
915mm 1530mm 2130mm 3050mm
15° 915mm 1530mm 2130mm
22° 3050mm
30° 760mm 1370mm 1830mm
44° 1860mm
44° 610mm 1220mm 1675mm

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

A Aluminium
F Flat Armoured
W Wire Armoured
Y Outer PVC Insulation Sheath
W Steel 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

Go back to Rules ↑

6. 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

Go back to Rules ↑

7. Load as per Sq.Ft

Type of Load Load/Sq.Ft Diversity Factor
Industrial 1000 Watt/Sq.Ft 0.5
Commercial 30 Watt/Sq.Ft 0.8
Domestic 15 Watt/Sq.Ft 0.4
Lighting 15 Watt/Sq.Ft 0.8

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8. Size of Ventilation Shaft

Height of Building in meter Size of ventilation shaft in sq meter Minimum size of shaft in meter
9.0 1.5 1.0
12.5 3.0 1.2
15 and above 4.0 1.5

Go back to Rules ↑

About Author //


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.


    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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