1-pole AFCI as 120V subpanel feeder

[tonyi]

This is a thought experiment I've been pondering.

Imagine load calcs for a couple of BRs indicated that the pair of them could be served by a single 20A branch. You could run #12 and use one breaker, but this has the disadvantage of taking out both BRs if it tripped, #12 is harder to handle, slower to install, fills boxes quicker, etc.

What would prevent using a single 20A AFCI as a 120V feeder to a 2-slot panel with a pair of ordinary 15A breakers in it? They're listed for feeders as well as branches. Downstream stuff would be protected, and it would wind up cheaper than using a pair of 15A AFCI's on the #14 wire.

[edit: what got me thinking about this are these microscopic sized bedrooms often found in Victorian and turn of the century places where there's room enough for a bed/dresser and not much else. There's really no room for a bunch of high powered stuff in one.]

[ January 03, 2004, 10:43 AM: Message edited by: tonyi ]

 

[iwire]

Re: 1-pole AFCI as 120V subpanel feeder

Tony, I doubt the cost of the panel and breakers would be less than the cost of the 12 AWG and perhaps some larger boxes.

Beyond that 215.2(A)(2)(1) would require the feeder to be 30 amps minimum regardless of load calcs.

I would also wonder about feeding a 250 volt 3 wire panel with 120 volt 2 wire? (listing)

Would you consider feeding a 3 phase panel single phase?

Bob

 

[jimwalker]

Re: 1-pole AFCI as 120V subpanel feeder

I could easily see 3 bedrooms on 1 afci breaker.If i am correct all i need is 3 watts fer sq ft.
14-2 =1800 watts= 600 sq ft of bed rooms.
You might easily be kicking breaker and have unhappy customer,but i believe your legal.
I see nothing wrong in maybe 2 bedrooms on 1 afci.
Min.code will not keep happy customers
I too fail to see any savings in that extra panel

[ January 03, 2004, 07:12 PM: Message edited by: jimwalker ]

 

[tonyi]

Re: 1-pole AFCI as 120V subpanel feeder

I'd considered the 215 point previously, but all it really requires is 30A feeder ampacity - there's no requirement I could find forcing you actually to feed it with that much. Just means a piece of 10-2 rather than 12-2 for the feeder. The panel is still a 1 phase panel, it just won't be doing any 240V branches

I don't view this notion a something you'd want to do in new work, rather something that might be useful in certain specific rework situations. Some of the old metal boxes are awful shallow, getting new #12 MC or Romex in them is a fill violation. #12 AC can work, but the stuffing is a lot more tedious than #14 and I've never been fond of internal box clamps when using AC, they just don't cinch down all that well.

Jim, the aim here would be to improve the usability of something that's bad. A lot of these older places maybe have one or two 15A branchs running virtually all the commonly used lights and recepticals in the place (outside of the kitchen). The idea is to add a bit more capacity and be able to partition up the existing branch(s) in a more logical manner so the whole place doesn't go dark and the existing wire isn't running as maxed out as it was.

Frequently there'll be a few strategic spots in a basement where some maxed out branch can be split up very easily and give excellent bang for the buck in usability returns.

[ January 03, 2004, 07:33 PM: Message edited by: tonyi ]

 

[iwire]

Re: 1-pole AFCI as 120V subpanel feeder

Point taken on the feeder.

I am not sold on the panel.

 

[jxofaltrds]

Re: 1-pole AFCI as 120V subpanel feeder

"10-2 rather than 12-2 for the feeder"

Do you mean a 10-3wg? Isn't this a "panel"? Are you allowed to have a panel fed by one leg?

"If i am correct all i need is 3 watts fer sq ft."

No limit in a residential application for the number of receps on one circuit.

Mike P.

[ January 04, 2004, 08:44 AM: Message edited by: jxofaltrds ]

 

[tonyi]

Re: 1-pole AFCI as 120V subpanel feeder

This is sort of the crux of the question Mike - there's nothing I can find in the NEC that would preclude a single leg subpanel. Couldn't load balance it, or get 240V off it, but in some cases that might not be an issue.

I think many years ago there may have been some small single leg services put in...

The point how its listed seems valid, I'm going to call Cutler tomorrow and ask'em what their take on using one this way would be.

To add more confusion to this - suppose the branches in such a 1-leg sub were all the same size as the feeder. Now whats the electrical difference between this sub and a multi-gang switch box with a single 20A feed? The breakers in the sub will undoubtedly be SWD, breakers are switches, well you can see where this thought track is going...

 

[jxofaltrds]

Re: 1-pole AFCI as 120V subpanel feeder

Tonyi

Thanxs. I would like to know.

We do alot of what ifs here. Althought we would never do it (some of the examples), it is good to know what is code compliant.

Mike P.

 

[tonyi]

Re: 1-pole AFCI as 120V subpanel feeder

Well, I called Cutler today and their engineering people said it would work OK and be safe in reality, but it would have a UL listing problem.