Cannibalizing 240V Circuit

[Michael Armstrong]

Practically speaking, I think your example is fine, as long as the breaker is 15A or less. For an extreme example, suppose some genius invents a laser-powered range that only uses 10A. But he notices that the thousands of old ranges he wants to replace have those giant plugs on them, and a corresponding 50A receptacle, so he ships his new range with a plug that will go into the existing receptacle. Great. But if you're building a new house, you don't want to waste money on a long run of 8/3 for a 10A load, so you use 14/3 and a 15A breaker, and a 50A receptacle. I see no problem with that. It's the breaker's job to protect the wiring, and it doesn't care what happens downstream. If a new owner brings his old range in and plugs it in, *pop* and we're all OK. I'm sure the code will eventually require a warning placard or something, but if the new owner replaces the 15A breaker with a 50A, that will be self-correcting .

 

[Quatrix]

Good Day and Happy Holidays,

Purpose: Splice two sets of 12AWG (BLACK, WHITE, Bare GND) to one set of 10AWG (BLACK, RED, WHITE, Bare GND). One set will connect to one receptacle and the other set will connect to another receptacle in another bathroom.

My plan:

1. Use the 3-way connector 221-613 to tie the 10AWG, 12AWG, and another separate 12AWG, WHITE neutral conductors together

2. Use another 3-way connector to tie all bare grounds together

3. Use the 2-way 221-612 connector to tie the 10AWG and 12AWG BLACK conductors together

4. Use another 2-way connector to tie 10AWG RED and 12AWG BLACK conductors together

5. Replace two-pole 30A with a two-pole 20A breaker

Please refer to my wiring diagram, two-pole breaker, and feel free to make any comments or suggestions.

 

[Michael Armstrong]

I'd be real surprised if those push-in connectors accommodated 10AWG. Also, there might be a couple code problems, since bathrooms are involved.

 

[bud16415]

I would just twist them and use proper sized wire nuts. Space might be a problem in that Jbox with connectors. Then get a proper blank cover for the box.

 

[Quatrix]

Looking through their data sheet these connectors are rated for 20 – 10 AWG. After installation, each wire was given a good tug to ensure each is tightly secured. Most reviews are positive about these connectors.

https://www.wago.com/us/wire-splicing-connectors/compact-splicing-connector/p/221-612

Michael Armstrong,
For my own curiosity, where in the NEC does it mention that we are not allowed to cannibalize a 240V circuit for 120V, then use the two circuits for bathroom receptacles?

 

[Michael Armstrong]

Looking through their data sheet these connectors are rated for 20 – 10 AWG. After installation, each wire was given a good tug to ensure each is tightly secured. Most reviews are positive about these connectors.

https://www.wago.com/us/wire-splicing-connectors/compact-splicing-connector/p/221-612

Michael Armstrong,
For my own curiosity, where in the NEC does it mention that we are not allowed to cannibalize a 240V circuit for 120V, then use the two circuits for bathroom receptacles?

It doesn't; I apologize. But all bathroom receptacles now must be AFCI protected, can't share a circuit with any other non-bath room, and with this configuration you've got a "multiwire branch circuit" with a shared neutral, which will mess up some AFCIs, if they're in the service panel. You're OK on the non-bath room issue, I suspect individual AFCIs in the bathrooms would work, and the newer GEs in the service panel would work.

 

[Quatrix]

Mike,

You brought up a very good point.

I only have one dual function, QO, 20A, Single-pole breaker (https://www.homedepot.com/p/Square-...I-and-GFCI-Circuit-Breaker-QO120DFC/204844647) in a non-bathroom area. The circuit is a dedicated circuit and does not share neutral with any additional circuits.

All other breakers in the home are of regular type (thermal-magnetic) without any GFCI/AFCI protection.

Reading through nuisance tripping of AFCI breakers I came across the following article:

https://inspectapedia.com/electric/AFCI_Nuisance_Tripping.php

The way I understood, nuisance tripping is dependent upon the connected load, otherwise shared neutrals could be OK. As written in the subject article, nuisance tripping occurred on an AFCI circuit where a coffee maker was connected, sharing the neutral with a “string of electrical receptacles”. Another three additional AFCI breakers were installed in the same electrical panel, with one of them being in active use. This one breaker also had a string of receptacles connected, powering lighting and computer equipment – did not have nuisance tripping. The way I understood, in both cases neutral wire was shared among the receptacles, otherwise what would make them be called a string of receptacles? As far as the multi-wire branch circuit discussed in this topic, apart from the AFCI jazz, I think the wiring diagram is correct. There is nothing connected to the two 120V legs except for the two bathrooms' receptacles. Please confirm if my reasoning is correct.

P.S.

By sharing (multi-wire branch circuit) I mean a scenario as shown in the image below where the load power (RED or BLACK) wires are separately tied together and all neutral wires are also tied together. Each receptacle is sharing either the RED wire power leg or the BLACK wire power leg. All of them are tied to the same neutral wiring. I have also provided helpful links on AFCI (for curious people).



http://apps.geindustrial.com/publibrary/checkout/DEA-635?TNR=Brochures|DEA-635|PDF&filename=DEA-635.PDF

https://apps.geindustrial.com/publibrary/checkout/DET-719?TNR=Application and Technical|DET-719|generic

 

[Quatrix]

Happy New Year to All,

Does anyone have any ideas regarding my previous post? It would be interesting to read how a veteran of the trade understands the issue.

 

[Michael Armstrong]

I installed a QO "Combination AFCI Circuit Breaker (CAFI)" breaker a few months ago. Note it was not specifically an AFCI/GFCI. It also had built-in diagnostics, which detected shared neutrals and tripped it if found one:


Square D tech support was very confused about this, and tried to tell me it was a GFCI as well, but it wasn't - mine detected a fault to ground, but didn't meet the GFCI "fault" standard. There was a long discussion about this on the forum a while back, but I can't find it now. Yours is apparently a newer, more robust true AFCI/GFCI model.

GE is quite proud of their AFCI, which apparently functions properly even if there's a shared neutral.

 

[afjes_2016]

"Square D tech support was very confused about this, and tried to tell me it was a GFCI as well, but it wasn't"

Not surprised at all about this confusion - but coming from a tech support rep he/she should have known better.

This subject is a big misconception on the layman/DIYer. They see the word "combination" and assume the combination refers to being a AFCI and a GFCI when in fact the word combination only refers to the sensing of the AFCI of either a parallel arc or series arc. The "C" such as in CAFCI leads them in the wrong direction in thought.

The true name for a device such as a breaker that is both rated for AFCI and GFCI protection is a "dual" function and not "combination".