3 wire circuits and arc fault breakers

[homeowner in burbank]

I'm extending one leg of a three wire circuit and the inspector wants an arc fault breaker on it.

Do two pole arc fault breakers work effectively on three wire circuits, or is it going to be tripping all the time?

 

[Stuff]

Works find as long as you don't have a neutral/ground fault issue. Some brands/panels easier to deal with. The new GE's don't check for ground fault at all.
Note this is 30ma ground fault. Not the 5ma that GFCI breakers check for.

 

[Sponsor]

 

[homeowner in burbank]

Works find as long as you don't have a neutral/ground fault issue. Some brands/panels easier to deal with. The new GE's don't check for ground fault at all.
Note this is 30ma ground fault. Not the 5ma that GFCI breakers check for.

The "ground" is the flex conduit the wire was run in 30 years ago.

Am I screwed?

 

[Jadnashua]

A GFCI doesn't need a ground wire to work properly. Arc fault (at least as I understand it) has a 'tuned' circuit to listen for literally an arc from a loose connection. Since there should never be current in the ground wire unless there's a fault (generally, while the current might be going to ground, it may not be the actual ground wire that's providing that path), it will probably work. A bit more research is probably required.

One reason some don't like arcfault is based on the early designs...they ended up tripping much more often than they really should. It is designed to detect a loose connection that is arcing under load, and some appliances make a close approximation to a real fault.

 

[Stuff]

You should be fine as long as the neutral is not connected to the ground anywhere down the line.

 

[homeowner in burbank]

I am considering an alternative: to use an arc fault outlet in the place where the two circuits diverge. I only need to protect the new work, should be cheaper and less likely to trip.

 

[Kreemoweet]

I am considering an alternative: to use an arc fault outlet in the place where the two circuits diverge. I only need to protect the new work, should be cheaper and less likely to trip.

Unless there's a local amendment to the electrical code that provides otherwise, the latest NEC releases require AFCI protection for the
ENTIRE circuit when there's an extension made, not just the newly extended part of it.

 

[homeowner in burbank]

Unless there's a local amendment to the electrical code that provides otherwise, the latest NEC releases require AFCI protection for the
ENTIRE circuit when there's an extension made, not just the newly extended part of it.

Yes, we'll see about that. It is a QO panel and I am not sure that these breakers are available in QO. Happily this inspector is not a hard ass. Think good thoughts.

 

[Cacher_Chick]

Yes, we'll see about that. It is a QO panel and I am not sure that these breakers are available in QO. Happily this inspector is not a hard ass. Think good thoughts.

There is no difficulty in getting AFCI breakers for a QO panel.

 

[Kreemoweet]

https://www.homedepot.com/p/Square-...rc-Fault-Circuit-Breaker-QO220CAFIC/204844654

 

[homeowner in burbank]

There is no difficulty in getting AFCI breakers for a QO panel.

OK. Plus there is not room to swing a dead cat in that panel.

 

[homeowner in burbank]

Here's a QO arc fault breaker with no neutral pig tail:

https://www.homedepot.com/p/Square-...c-Fault-Circuit-Breaker-QO115PCAFIC/204860225

Does this mean it will perform in a three wire circuit without trouble?

Gotta call Square D.....

 

[Stuff]

That breaker is for a single pole circuit. More importantly it can only be used in a relatively recent QO panel that supports the plug-in neutrals.

I'm still not sure of what or how your panel is set up. Can you post pictures ?

 

[homeowner in burbank]

Well, I want to protect only one circuit, but in a three wire circuit. It is not a new QO panel. I have no Idea why one would choose a QO panel when cheaper and equal panels are available from Square D and Murray. I don't know anything about the plug-in of neutrals, but I am nearly sure that this panel is not one of them.

A photo would mostly show the mass of wiring in the panel. I fear needing to trace any wires in that panel.

 

[Cacher_Chick]

Well, I want to protect only one circuit, but in a three wire circuit. It is not a new QO panel. I have no Idea why one would choose a QO panel when cheaper and equal panels are available from Square D and Murray. I don't know anything about the plug-in of neutrals, but I am nearly sure that this panel is not one of them.

A photo would mostly show the mass of wiring in the panel. I fear needing to trace any wires in that panel.

Since you are planning to live there, it might be a good idea to take the time to clean it up.

 

[Kreemoweet]

Well, I want to protect only one circuit, but in a three wire circuit. It is not a new QO panel. I have no Idea why one would choose a QO panel when cheaper and equal panels are available from Square D and Murray. I don't know anything about the plug-in of neutrals, but I am nearly sure that this panel is not one of them.

A photo would mostly show the mass of wiring in the panel. I fear needing to trace any wires in that panel.

A "three-wire circuit" is what is known to electricians as a "multiwire branch circuit". It is ONE circuit, not two, and the two-pole breaker I
posted above (with perhaps a different rating to match your existing circuit) is what you need to meet current electrical code requirements. It will
work fine, provided your existing wiring is not messed up. QO panels are excellent, and preferred by many.

 

[homeowner in burbank]

QO tandem breakers are priced as if they were shed by unicorns. I've never found flaw with a Murray panel, nor a Square D homeline, both of which have a full selection of breakers (including tandems with both 15 and 20 amp toggles) and four pole tandems that really free up space.

I appreciate the confirmation that a two pole breaker will serve (assuming there is no flaw in the existing circuit.) The panel is pretty full and I don't know if I can juggle the single pole breakers around enough to free up two spaces. I am always fretting about inadvertently putting the red and black leg of a multiwire circuit on the same side of the phase, thus stressing and likely destroying the neutral. Gotta concentrate.

 

[Jadnashua]

You should never be using a 3-wire circuit without it being powered by a tandem breaker.

 

[homeowner in burbank]

You should never be using a 3-wire circuit without it being powered by a tandem breaker.

Jim, sorry, tandem vs twins. Yes, it is currently required that three wire circuits be fed by two pole breakers with a common disconnect (and you might call that tandem, where I am referring to two independent breakers fitting in one slot as tandem; possibly you would call that a twin) , that requirement post dates the assembly of the panel in question. Another argument against QOs. One can buy a Murray breaker that has four poles in two spaces, with the inner two ganged together, and the outer two ganged together. In various current combinations. A clean installation unavailable (as best as I know) in QO.

 

[Stuff]

Not a lot of selection in QO land but there is this one. Also non-CTL so only legal for old panels. They call it a quad tandem but I'd call it a triplex - QO20303020 - https://www.rexelusa.com/usr/Root-C...,-20A,-1-2P,-30A,-120-240VAC,-10kAIC/p/214387
I don't think the center double pole 30 is common trip as cut sheet shows two separate tandems. So I guess you could take CTL tandems and use handle ties as well for MWBC.

From their catalog page:

Order two QOT1515 or QOT2020 circuit breakers and handle tie, catalog #QOTHT, for commonswitching of center double-poles.