Residential MWBC & AFCI Question

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MikeS

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Location
Chapel Hill NC
Looked @ a job the other day for bid - customer wants to finish off an attic space for a home office. When the house was built, the original EC Pulled a 14/3 "spare" circuit up there for future use.
I like to separate lights from receptacles when I wire a room, plus, with cans & whatever office equipment he may have, he might exceed 15A for the room, especially when vacuuming/ cleaning. The sub panel in the basement that feeds the circuit is GE & they don't make a combo 2 pole AFCI Breaker. To keep costs down and minimize damage to finished portions of the house, I'm trying to avoid pulling a new wire from the basement to the attic.

Can I install a tiny 4 space subpanel up there, fed by the 14/3 and arc fault the 2 circuits from there? Having trouble finding code ref on this one....

Thanks in advance
 
S

Strife

Senior Member
There was a commercial for something a few years back in Florida, it went something like this:
"Driving in the exact change lane without exact change, NOT OK. Going through the exact change lane without a car, but with exact change: WEIRD, but OK"
I don't think there's anything that prohibits that, weird to have a panel fed by a 15A breaker, but I think it's OK.

MikeS said:
Looked @ a job the other day for bid - customer wants to finish off an attic space for a home office. When the house was built, the original EC Pulled a 14/3 "spare" circuit up there for future use.
I like to separate lights from receptacles when I wire a room, plus, with cans & whatever office equipment he may have, he might exceed 15A for the room, especially when vacuuming/ cleaning. The sub panel in the basement that feeds the circuit is GE & they don't make a combo 2 pole AFCI Breaker. To keep costs down and minimize damage to finished portions of the house, I'm trying to avoid pulling a new wire from the basement to the attic.

Can I install a tiny 4 space subpanel up there, fed by the 14/3 and arc fault the 2 circuits from there? Having trouble finding code ref on this one....

Thanks in advance
Click to expand...
 
ceb58

ceb58

Senior Member
Location
Raeford, NC
Can I install a tiny 4 space subpanel up there, fed by the 14/3 and arc fault the 2 circuits from there?
Click to expand...

I like to separate lights from receptacles when I wire a room, plus, with cans & whatever office equipment he may have, he might exceed 15A for the room, especially when vacuuming/ cleaning
Click to expand...
.

Your OCP to this sub would still be 15 amp. The only thing it would allow you to do is install AFCI.


Is the main panel Siemens?
Click to expand...

OP stated main panel is a GE.... But isn't Siemens listed for replacement in a GE? I think what 480 is getting at is Siemens makes a 2 pole AFCI that will work on MWBC. But you are still limited to 15 amps.
 
cadpoint

cadpoint

Senior Member
Location
Durham, NC
Be sure you explain this to the home owner, I'd strongly suggest more circuits.
You have to state that you believe that the first thing the owner will do is max out his little 15 Amp circuit.

Try to get them to understand all the various situations of appling power to this space, if they need A/C,
or even add a temp heater they will totally be out of luck.

Your not relieving any of the circuits that are up there with a panel as you suggest!
 
M

MikeS

Member
Location
Chapel Hill NC
I can accept weird

I can accept weird

Thanks for the quick responses!

I can deal with weird & unorthodox, illegal is a different matter:roll:
Of course I'll clear my idea with the ahj before I proceed, just wanted to get other opinions first.

The main panel located in the center of the house is Square D. The home is a pseudo timber frame with lots of exposed woodwork, open airy spaces-- a real nightmare to fish anything so I'm trying to make do with what is already there...
Life hands you lemons, make limoncello!
 
M

MikeS

Member
Location
Chapel Hill NC
cadpoint said:
Be sure you explain this to the home owner, I'd strongly suggest more circuits.
You have to state that you believe that the first thing the owner will do is max out his little 15 Amp circuit.

Try to get them to understand all the various situations of appling power to this space, if they need A/C,
or even add a temp heater they will totally be out of luck.

Your not relieving any of the circuits that are up there with a panel as you suggest!
Click to expand...

As far as heat & A/C is concerned the unit serving the upstairs is in the attic access area adjacent to the office, so that, fortunately won't be an issue, I'll be sure to line out the limitations of the circuit(s) on the contract, if the job proceeds...
 
david luchini

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
ceb58 said:
.

Your OCP to this sub would still be 15 amp. The only thing it would allow you to do is install AFCI.
Click to expand...

I think the OP is suggesting that rather than using two wires of the existing 14/3 from one 15A AFCI c/b in the main panel, he'd use the 14/3 as 2 phase + neutral from a 15A-2P c/b to feed a 120/240 sub panel and install two 15A AFCI c/b's in the sub panel giving him two 15 amp circuits in the converted attic space.

In effect, he'd have 3600VA of circuit capacity instead of only 1800VA.
 
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M

MikeS

Member
Location
Chapel Hill NC
ceb58 said:
.
OP stated main panel is a GE.... But isn't Siemens listed for replacement in a GE? I think what 480 is getting at is Siemens makes a 2 pole AFCI that will work on MWBC. But you are still limited to 15 amps.
Click to expand...

I'm not seeing the Siemens listed for other enclosures... I give them a call next week.
Regarding OCP, yes, 15 amps but, for each circuit--15 lights and 15 receptacles.
 
M

MikeS

Member
Location
Chapel Hill NC
Precisely!

Precisely!

david luchini said:
I think the OP is suggesting that rather than using two wires of the existing 14/3 from one 15A AFCI c/b in the main panel, he'd use the 14/3 as 2 phase + neutral from a 15A-2P c/b to feed a 120/240 sub panel and install two 15A AFCI c/b's in the sub panel giving him two 15 amp circuits in the converted attic space.

In effect, he'd have 3600VA of circuit capacity instead of only 1800VA.
Click to expand...

Yes, that is exactly what I'm thinking!

Mike
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Mike , GE may make a DP arc fault combo style-- I would check with Moe but personally I would rather see the panel-- it is perfectly legal and a fix for situation where they have a panel such as Homeline which , I believe, does not make a DP combo arc fault.

You should have no issues with the panel idea. Obviously you couldn't run a 20 amp circuit from this panel for , say a bathroom, and expect that to pass. :D
 
M

MikeS

Member
Location
Chapel Hill NC
Dennis Alwon said:
Mike , GE may make a DP arc fault combo style-- I would check with Moe but personally I would rather see the panel-- it is perfectly legal and a fix for situation where they have a panel such as Homeline which , I believe, does not make a DP combo arc fault.

You should have no issues with the panel idea. Obviously you couldn't run a 20 amp circuit from this panel for , say a bathroom, and expect that to pass. :D
Click to expand...

Already spoke with Moe and he said Noe!:D GE doesn't yet. Hence the panel solution...
 
Jim W in Tampa

Jim W in Tampa

Senior Member
Location
Tampa Florida
Your idea is OK, I would rather see you add the panel next to the other and buy combo breaker. Also your not solving much if lights are on just 1 side. Rather see lights and perhaps a receptacle just under light switch for the vacume or any other unnormal items in office. Also smart to tell them to buy a small plug in ups for computer equipment. All of our computers have them $200 now saves a computer and what ever work they are in middle of.
But 3600 watts is plenty for typical home office. Assuming normal printer
 
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