ECN Forum Forums General Topics of the Trade General Discussion Area Standard vs Optional Calculation

Just wanted to see what the most popular method is for calculating the service load for residential installations, the standard or optional. It seems to me that the standard calculation is more conservative. Has that been your experience out there?

There are requirements t hat must be met listed in 220.30A before you can use the optional method. You project may not meet the requirements.

[This message has been edited by Bob (edited 01-17-2005).]

Hey EE,
I've done it both ways in the past. I'm not sure what you mean by [e]conservative[/e], but I've found that most of the time the standard calculation results in a larger service. I haven't done any of these calculations, with the exception of my own house, in years. I used the standard calculation on my house. It seems like there were a few times when the optional method resulted in a larger service, but not very often.

Wattologically Yours,
Doc

As an inspector, I never see the standard method used. My experience is the same as Doc's, which is that the optional method results in a smaller service/feeder.

What I meant by conservative is that the calculated service size would be larger using the standard method vs the optional method. From the perspective of a practicing EE who worries about liability issues, and often not knowing exactly what the appliance and heating/air cond. ratings are, or how they might get changed during the construction phase, it seemed prudent to me to use the more conservative method, better safe than sorry. I wanted to see which method the experience base out there is using.

Practicing EE,
Looks like we are on the same page.
Regards,
Doc