Section 220.82

[jones26r]

When do I use the optional calculation method in section 220.82? I know about the standard method, but when exactly is the optional method used?

I inputed the same figures for both methods and my results were not the same. This could throw-off calculations if the correct method is not used.

 

[bphgravity]

Either / or. It's a choice. The standard method is typically more conservative.

 

[charlie b]

The whole idea of the optional method is to give you, well, to give you an option. Do the problem both ways, and use the method that gives you the smaller answer.

But keep in mind that the NEC only gives you the minimum requirements for a safe installation. The owner of a new building project might want more than the NEC minimums. So the number you use when you actually build the facility is a matter between yourself and the owner's wallet.