Ground Fault

[Miguel c]

Why does not an EGC burn up when there is a grount fault in which for example a 8 AWG wire carries 583 A to the source in order to trip the breaker?

 

[Dsg319]

There’s others that can answer your question in way more detail, but I’m a nut shell it only has that current on it for a very short amount of time to operate the OCPD quickly.

 

[mbrooke]

Why does not an EGC burn up when there is a grount fault in which for example a 8 AWG wire carries 583 A to the source in order to trip the breaker?

At 583 amps on 8 AWG conductor has a 50% chance of melting it open.

Table 250.122 allows 8 AWG on OCPDs up to 100 amps. 583/100= 5.8 or an opening time between 2 and 10 seconds. This time will be longer if your starting current is 583 amps vs the finishing current as the resistance of the copper wire goes up 0.393% for every 1*C rise.

https://library.industrialsolutions.abb.com/publibrary/checkout/GES-6203B?TNR=Time%20Current%20Curves%7CGES-6203B%7CPDF&filename=GES-6203B.pdf

According to this, 472 amps will melt #8 in 10 seconds:

American wire gauge - Wikipedia

en.wikipedia.org

For this reason, you must calculate the loop impedance of all circuits to make sure a breaker's opening time is faster than the EGC's adiabatic limits.

For reasons of resistance rise and to prevent ignition, the final short circuit temperature of PVC wire should not exceed 150*C, and 250*C for XLPE.

If in doubt use a full size EGC for circuits 60 amps and below, half size in relation to the mm2 for circuits over 60 amps.

 

[don_resqcapt19]

Table 1 in this Bussmann pubication gives some guidance for this issue.

This calculator lets you play around with the numbers. It Insuated Cable Engineers Association considders a temperature of 150°C to be the maximum short time conductor temperature to avoid damage to the insulation.

 

[Miguel c]

There’s others that can answer your question in way more detail, but I’m a nut shell it only has that current on it for a very short amount of time to operate the OCPD quickly.

I came to the same conclusion, however I was not sure, but I thank you very much for answering and confirming this important information.