220.83(A) Existing Dwelling Unit Load Calculation

[wwhitney]

Why is 220.83(A) different from 220.83(B)?

It seems like when you are adding non-HVAC loads to a dwelling unit, 220.83(A) doesn't break out the A/C and electric space heating loads separately, so they end up lumped in with everything and with a 40% diversity factor. While 220.83(B) does break those loads out separately, and then gives them a 100% factor.

The upshot being that 220.83(A) would always give a lower number than 220.83(B). I can't see any technical justification for this distinction.

Thanks,
Wayne

 

[tortuga]

All I can say is the original intent in '74 when it was added was to allow people to squeeze a little more out of widespread existing 60 amp services:

Then in '84 there were a number of proposals to drop the 60A restriction one of them was by the sponsor of this forum.

 

[wwhitney]

Looks like that version of the text has the same dichotomy, in that the last paragraph starts "if [electric HVAC equipment] is to be installed," then you use the 100% factors.

But logically that should have been "whenever [electric HVAC equipment] is installed". So is this just a 50 year old error that has never been corrected?

I did check the First Draft ROPs back to 2004 to see if anyone had proposed just eliminating 220.83(A) in favor of the computation in 220.83(B) for all cases. But there were no such proposals in the last 20 years.

Cheers, Wayne

 

[Tainted]

All I can say is the original intent in '74 when it was added was to allow people to squeeze a little more out of widespread existing 60 amp services:
View attachment 2563945
Then in '84 there were a number of proposals to drop the 60A restriction one of them was by the sponsor of this forum.

I've asked the same questions as wwhitney and forever wondered about this code. 220.83 was such a mystery to me and why it was ever in the code in the first place. You cleared it up just a little but it still calls for HVAC units to be at 100%