Adiabatic formula

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Farmelectrics

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• Feb 3, 2012

• #1

Not got my reqs or on site guide with me today could some one explain or show me an example to work out earth size 230v supply ze = 0.12 customer been told about calculation rather than need to upgrade earth system and i cant remember formula or how to do it thanks in advance lads

 

telectrix

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• Feb 3, 2012

• #2

I = 230/0.12 = 1.92kA.

S= sq.rt. ( Isq. x 0.1 ) /143.

 

Last edited: Feb 3, 2012

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Farmelectrics

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• Feb 3, 2012

• #3

telectrix thanks for help but how would i calculate what size earth cable to use for installation by the above formula not done this before allways put in 16mm main earth 10mm water and gas thanks

 

Richard Burns

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• Feb 3, 2012

• #4

Minimum earth size using the formula and values tel has given from you readings is 4.24mm2 anything above that and you can assume adequate but if fitting would need to be subject to minimum size for earthing system.

 

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• Feb 3, 2012

• #5

richard thanks for advise but coukld you explain step by step how you got that if you dont no ask always been my policy once ive been shown will store in my human hard drive many thanks

 

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brman

• Feb 3, 2012

• #6

have a read through this thread, I think it gives the info you need....
http://www.electriciansforums.net/e...egulations/50345-adiabatic-earth-bonding.html

 

Richard Burns

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• Feb 3, 2012

• #7

this is how I did it

 

i=p/u

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• Feb 3, 2012

• #8

there is no set values for main earth, just main protective bonding, minimum 6mm for tns,tt and minimum for tnc-s 10mm,

the valuers are in the book if you cant be bothered too count

 

B

brman

• Feb 3, 2012

• #9

i=p/u said:

there is no set values for main earth, just main protective bonding, minimum 6mm for tns,tt and minimum for tnc-s 10mm,

the valuers are in the book if you cant be bothered too count

Click to expand...

except it is a minimum of 4mm2 for any unprotected protective conductor according to 543.1.1.

 

D

Deleted member 26818

• Feb 3, 2012

• #10

With TN-C-S the minimum is 10mm², as the earth conductor is treated the same as a bonding conductor.
However, a smaller CSA could be deemed as adequate, if there is no evidence of overheating.