One more multifamily question

[laramie]

When i prepare the calcs, by using the standard method it shows i need a service of 1320A = 1600..

if i use the optional method, i come up with a calc of 1024A = 1200..

why is there such a big difference in the standard vs optional methods.. and why wouldn't someone ALWAYS use the optional method for calcs if it proves a smaller service can be installed??

 

[steve66]

Re: One more multifamily question

I don't think you will always get the same results. In some cases, the optional method may give a larger service size. Thus, do both calcs and take the smaller of the two, if you wish.

Steve

 

[charlie b]

Re: One more multifamily question

I agree with that advice: do it both ways. I haven't had to do a vast great number of load calculations. But I have yet to see a case in which the optional method gave the higher result.

It might be worth having a conversation with the owner. There might be some plans for future expansion. The owner might appreciate learning that the NEC just gives the minimums for a safe installation, but that the customer's ultimate satisfaction might require going beyond code minimums.