Standard Method vs Optional Method

[sparkyman51]

I’m new to the electrical world and wondering which method should be used in the case that the results for either method derive different service sizes.

Example:
Standard method - 290 amps / 400 service
Optional method - 203 amps / 225 service

Can the optional method be trusted to have enough power in most cases? Or should the standard method be used to make sure that you are covering yourself from being short?

 

[LarryFine]

Can the optional method be trusted to have enough power in most cases? Or should the standard method be used to make sure that you are covering yourself from being short?

Welcome to the forum.

Either, depending on how you judge the likelihood of actually exceeding the optional ampacity.

Generally speaking, commercial is likely to be more highly loaded than residential.

 

[Birken Vogt]

I feel like either method rather grossly oversizes the number. So I pick whichever one suits me best.

I use a spreadsheet that allows you to switch back and forth after entering all the numbers.

 

[charlie b]

If you give the results of your article 220 service load calculation to the serving utility, they are likely to provide a service transformer rated around 40% to 50% of that value. They base that decision on long experience of design loading versus actual loading. In your example, I would be comfortable with the 225 amp service.

 

[tortuga]

I always use the optional calcs unless the odd case I am not allowed to.
For example the I recently started an optional dwelling unit calc 220.82 then realized I had a dwelling with a guest suite (ADU) so I had to use the standard calc.
Also there are times I have to use both, like mixed commercial / residential services, apartments over a commercial space.
I used the optional for the feeders to the dwelling unit but a general calc for the service equip / service entrance conductors for all units.