Earth Loop Impedance on COC test.

[ACEsterhuizen]

Page 276:

8.7.5 Earth fault loop impedance at the main switch:

8.7.5.1 At the main switch, the impedance shall be such that an earth
fault current double the rated current (or higher) of the main protective
device automatically disconnects the supply to the installation.

Table 8.2
indicates the earth fault loop circuits for different distribution systems. Page 277


https://www.tlc-direct.co.uk/Book/8.6.2.htm

http://www.ee.co.za/article/earth-lo...g-methods.html

http://www.elek.com.au/Files/Underst...0Impedance.pdf

http://mandrelectrical.com.au/karatings.php

So the Loop Test Result (eg 0.24 Ohms) in Ohms expressed in amps: A=V/z = 230/0.24 = 958 Amps
(Use the actual voltage and impedance readings.) The tester give you the psc amps anyway.

So your Main breaker is eg 60A. Your Earth Fault Impedance (0.24 Ohms) is such that a fault will result in 958 Amps flowing which is more than the "double or higher of your main protective device". (60A x 2( main breaker rating x double)=120A) as required by the reg. - so the earth fault impedance satisfy the regulation 8.7.5 because if you double your main breaker amps it is 120A and the earth fault that will flow is more than that and/or higher and will trip the breaker.

Lets say you loop impedance is 3 Ohms. So now 230/3=76AMps. So now the earth fault that will flow IS NOT more amps than the "double or higher than 120A" (which is double your main breaker 60A as required by regulation).

Note that the 76A fault might trip the breaker, but it does not satisfy the criteria required by regulation.

Your max amps that will flow on a fault is 958 amps, divide that by 2 (double the breaker rated amps) so the MAX amp breaker you can use on that loop impedance would be 479 amp breaker (theoretically)

So you record the 0.24 Ohms on the coc because it satisfies the regs and is correct.