Section 110.24 A

[WEILEROT]

As an electrical inspector, I see N.E.C. section 110.24 (Available Fault Current) not being addressed properly. Some electricians say "what is fault current" Others say I did not know that. I see arbritary numbers being place on service equipment. There was a large car dealership that went in in the city I inspect for. I was able to get the primary available fault current from the uitlity myself. I calculated the fault current my self based on the XFMR size and impedance, the calble length from the XFMR to the service equipment. The calculatioon that I came up with was not even close to the numbers the contractor had on the panel. Even figuring an infinite bus the numbers were not comparable. There was little motor contribution. So motor contribution was not a factor. In my opinion, I think a professional engineer should make the calculations. I submitted a public input for the 2017 (#3578) code cycle. My public input was not accepted. A professiona engineer submitted the same public input similar to mine and he received the same answer that I did. I just would like a general opinion on what other think. Please give me your opinion.

Herb

 

[Dennis Alwon]

I agree. Fault current calculations is not something an electrician should do but they do have the option of hiring an EE to do the calculation. Unfortunately most of us have no idea how to calculate it and when it comes to spending money to get it done- well you know the rest of the story.

 

[don_resqcapt19]

I have no issues if that label number exceeds what is actually available and the equipment has a rating equal to or greater than the available fault current listed on the label. This number is not used for anything other than proving that the correct equipment has been selected. There is only a hazard where the label shows a current that is less than what is actually available.