220.82 dwelling unit - 80% factor apply?

[malachi constant]

I am an electrical engineer and recently designed a multifamily dwelling. In meeting with the contractor a question came up about loads related to unit panel sizes. Try to follow me...

Part IV of 220 allows an optional feeder & service load calculation for dwellings. I used 220.82 Dwelling Unit to determine the ampacity of a given unit. All calculated ampacities on this project were between 80A and 96A. So I sized each feeder with #1 AWG conductors, and each panel at 100A.

The contractor thinks this is an issue for some/most of the panels - that each panel needs to be sized at 125% of the calculated load. I don't see that as a requirement in Article 220 or Article 408 Panelboards. Is it a requirement?

 

[nakulak]

230.42 a 1

 

[malachi constant]

Thanks. Thankfully I specified #1 AWG feeders (good for 130A) and I assume when I called out for "100A panelboards" we were going to be getting 125A rated panels 9will verify). So in this case it is a non-issue, but will keep in mind for future services.

 

[malachi constant]

Wait - after a second reading of 230.42(A) - this says we must take the calculation from Article 220 and from that add 100% of the non-continuous load to 125% of the continuous load.

So I used 220.82 to do my calcs. Should any of 220.82 be considered continuous? I would argue it should all be considered non-continuous. Is this defined anywhere? It is really hard to separate out any of the components of 220.82 and say one of them is definitely continuous. Let's take a look...

(B)(1) 3VA/sf for general lighting and receptacles - even though it includes "lighting" in the description you'd be hard pressed to say this number should be considered continuous.
(B)(2) 1500VA for small appliance branch circuit (laundry/washing machine) - not continuous.
(B)(3) and (4) fixed in place appliances. I assume some of these could maybe count as continuous: range, exhaust fan? But others wouldn't: dishwasher, garbage disposal, microwave, air conditioner, washing machine.
(C) Heating and AC. AC is not considered continuous, correct? Heating probably? If one is considered continuous and the other non-cont then the calculation gets considerably more complicated than intended.

I don't think the intent of 230.42(A) is to parse 220.82 like I just did. I assume the calculated result of 220.82 should be considered one big non-continuous load. Anyone have some insight - other interpretations?

Thanks in advance!

 

[cpal]

Dwelling loads are not generally considered be continuios. I don't think I've ever saw anyone treat them as such.

You need to increas the motor loads per unit IAW 220.14(C) and 220.18(A)

also read 220.14(I) and(J)

also 220.12states that the VA per Sq Ft shall constitute the minimum lighting load. I do not see it asking for an inc of 125% for loads operating 3 hours or more.