# Cannibalizing 240V Circuit



## Quatrix (Dec 16, 2019)

Good Day,

I need your help and advise regarding installation of a 20A, HTB series fuse holder (with fuse) inside of a box. The project will be done in a residential home, 240/120V, in the United States.  
*

Scope of Application*: I have a NEMA 10-30R receptacle in one of my bathrooms for what used to be the clothes dryer before I got rid of it. I do not use the clothes dryer, therefore my plan is to use one leg of the 240Vrms to connect to one of my 120V receptacles next to the sink in the same bathroom. In the NEMA 10-30R box I have the following: 1 Black Hot wire, 1 Red Hot wire, 1 White Neutral wire, 1 bare Ground wire. I have measured with DMM the voltages across the red to white = 120V, across the black to white = 120V, and across the red and the black = 240V. With such a combination I believe I am blessed to continue as planned, splice the #10AWG with a #12AWG, but please confirm on that. My question is how shall I aesthetically mount the fuse holder? By a simple search I have found the following link below which does not really express full details on the install, but does show an in-line fuse installation into a 6x6x4 box. Perhaps other experts on this forum may suggest even a better, more aesthetically pleasing installation. Please provide guidance and suggestions.

http://waterheatertimer.org/Fuseholder.html


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## Snoonyb (Dec 17, 2019)

Is the 10/3 in metallic flex, conduit or romex?


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## nealtw (Dec 17, 2019)

Change the double 30 breaker to a double 20 breaker and just run 12/2 from that junction box.


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## Jeff Handy (Dec 17, 2019)

nealtw said:


> Change the double 30 breaker to a double 20 breaker and just run 12/2 from that junction box.


Yes, great idea. 

And leave the existing outlet alone, just add another one. 
Always a need for more outlets, with hair dryers, toothbrushes, shavers, curling irons, etc. 

Or change a duplex outlet to a box with two duplex outlets. 
Of course, all of them should be gfci.


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## Quatrix (Dec 17, 2019)

Nealtw,

Yes, that is a good idea. But if we only had the option to install a fuse, which one would you go with? Panel mount vs. in chassis mount?

P.S. this is a photo of my box with the wiring inside. Also, I have sample images of fuse carriages with two types of mounting methods. I just wanted to see what would you select as the best way to mount it in this application?


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## bud16415 (Dec 18, 2019)

Quatrix said:


> Nealtw,
> 
> Yes, that is a good idea. But if we only had the option to install a fuse, which one would you go with? Panel mount vs. in chassis mount?
> 
> ...


First off I’m not a pro.


If it were mine and I no longer needed the 240v power I would do something similar to what Neal suggested. I would convert the breaker at the panel to the lower amp breaker and select one suitable for what is called a multi wire branch circuit. In that box then I would add two GFCI outlets one on each branch.


No way would I mount any kind of fuse and holder in that box as you are suggesting. Not to code.


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## kok328 (Dec 18, 2019)

Yea, I'd have to veto the fuse and go with reducing the breaker amperage to two 20 Amp circuits with a shared neutral.
However, I don't think reducing wire size is allowable.


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## bud16415 (Dec 18, 2019)

kok328 said:


> Yea, I'd have to veto the fuse and go with reducing the breaker amperage to two 20 Amp circuits with a shared neutral.
> However, I don't think reducing wire size is allowable.


As long as he pigtailed on #12 to feed two GFCI outlets I don’t see a problem. He’s really not reducing wire size he will just be feeding the multi wire branch with and oversized wire gauge.


I don’t think code has a problem with over spec on wire size.  


He does need a breaker where both circuits are on a tied or common handle though so when one is opened they both open.


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## nealtw (Dec 18, 2019)

this is not a car, bus or truck. there is no way in hell i would use inline fuses.


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## Quatrix (Dec 18, 2019)

nealtw said:


> this is not a car, bus or truck. there is no way in hell i would use inline fuses.


Neal,

Thanks for the feedback. This is the breaker I will purchase. 
https://www.homedepot.com/p/Square-D-QO-20-Amp-2-Pole-Circuit-Breaker-QO220CP/100032386
Also, would you suggest to feed one receptacle from one of the legs (e.g. from black and white, plus GND) and another receptacle in a different bathroom from the other leg (from red and white, plus GND)? That way, the current draw will balance out if both bathroom receptacles are being used at the same time, vice connecting both receptacles all from one of the legs, tying back and insulating the unused HOT wire.


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## bud16415 (Dec 19, 2019)

Quatrix said:


> Neal,
> 
> Thanks for the feedback. This is the breaker I will purchase.
> https://www.homedepot.com/p/Square-D-QO-20-Amp-2-Pole-Circuit-Breaker-QO220CP/100032386
> Also, would you suggest to feed one receptacle from one of the legs (e.g. from black and white, plus GND) and another receptacle in a different bathroom from the other leg (from red and white, plus GND)? That way, the current draw will balance out if both bathroom receptacles are being used at the same time, vice connecting both receptacles all from one of the legs, tying back and insulating the unused HOT wire.




At this point I’m going to suggest (with all due respect) that you hire a professional electrician and tell them your intended outcome and let them provide the products and do the work as to code. Just from what I’m reading I think this project is outside what I feel is safe and practical for you to do.


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## Quatrix (Dec 19, 2019)

*bud16415, *
That is why I am here, to get the feedback and learn about the process. I just asked a question in my previous post and would like to get a reasonable answer.


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## bud16415 (Dec 19, 2019)

Quatrix said:


> *bud16415, *
> That is why I am here, to get the feedback and learn about the process. I just asked a question in my previous post and would like to get a reasonable answer.



Well I gave you my input in post 6, 8 & 11. You were given some similar good advice in the rest of the answers.


Have you worked behind the panel before changed breakers etc?


If you feel comfortable change the breaker run from your Jbox to all new locations install a suitable Jbox / boxes and follow code as to proper wire size and GFCI outlets. The Jbox where this is now cannot be hidden but if you don’t want an outlet there it will need a blank cover. If you need more than one location as in a second bathroom I would make it a multi wire branch circuit and use both sides of the 240v.


https://www.twielectric.com/safety-...nal-electrical-code-multiwire-branch-circuit/


https://www.ecmweb.com/content/article/20886177/multiwire-branch-circuits-can-be-dangerous


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## nealtw (Dec 19, 2019)

Quatrix said:


> Neal,
> 
> Thanks for the feedback. This is the breaker I will purchase.
> https://www.homedepot.com/p/Square-D-QO-20-Amp-2-Pole-Circuit-Breaker-QO220CP/100032386
> Also, would you suggest to feed one receptacle from one of the legs (e.g. from black and white, plus GND) and another receptacle in a different bathroom from the other leg (from red and white, plus GND)? That way, the current draw will balance out if both bathroom receptacles are being used at the same time, vice connecting both receptacles all from one of the legs, tying back and insulating the unused HOT wire.


That looks like the right idea, breakers do have to match the breaker box you have. But yes a double pole 20 would be the answer.


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## Jeff Handy (Dec 19, 2019)

I think Square D makes at least two types of breakers, QO and Homeline. 
There should be a big chart inside the panel that lists the compatible breakers for that box.


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## kok328 (Dec 20, 2019)

bud16415 said:


> As long as he pigtailed on #12 to feed two GFCI outlets I don’t see a problem. He’s really not reducing wire size he will just be feeding the multi wire branch with and oversized wire gauge.
> 
> 
> I don’t think code has a problem with over spec on wire size.
> ...



Good catch on the tied breakers.

I fully realize the gauge of existing wire will now be considered over sized for the circuit and that code does not have a problem with over sizing your wire BUT, it does have a problem with reducing the size of the wire in the run.  Even though this reduction will be perfectly safe for the 20amp outlets, it still violates code.

P.S.- Just saying.  I'd do the same with pigtails.  Safer than trying to attach 10AWG to a 20AMP GFCI?


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## Michael Armstrong (Dec 20, 2019)

Can one of the pros tell me the code section that prohibits reducing conductor size?


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## kok328 (Dec 20, 2019)

Michael Armstrong said:


> Can one of the pros tell me the code section that prohibits reducing conductor size?



I think we are good to go here.  Reduction in wire size IS allowable as long as the reduction of wire size does not go below the rated amperage of the breaker.


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## Michael Armstrong (Dec 20, 2019)

kok328 said:


> I think we are good to go here.  Reduction in wire size IS allowable as long as the reduction of wire size does not go below the rated amperage of the breaker.


That's my feeling as well, but in #16 you said "[the code] does have a problem with reducing the size of the wire in the run. Even though this reduction will be perfectly safe for the 20amp outlets, it still violates code." I haven't been able to find that violation explicitly called out, and if it exists I'd love to know where.


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## kok328 (Dec 20, 2019)

Michael Armstrong said:


> That's my feeling as well, but in #16 you said "[the code] does have a problem with reducing the size of the wire in the run. Even though this reduction will be perfectly safe for the 20amp outlets, it still violates code." I haven't been able to find that violation explicitly called out, and if it exists I'd love to know where.



Yea, thought about code and how it applies to this situation and realized we do not have a violation here, and posted a correction to my previous statement.  Just me talking before thinking; again.
It would be a different story if we were going to pigtail from 10awg to say 14awg to a 20 or 30 amp outlet.  This is the type of situation that code is preventing and in this case does not apply.


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## Michael Armstrong (Dec 21, 2019)

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 .


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## Quatrix (Dec 27, 2019)

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.


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## Michael Armstrong (Dec 28, 2019)

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


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## bud16415 (Dec 28, 2019)

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.


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## Quatrix (Dec 30, 2019)

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?


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## Michael Armstrong (Dec 31, 2019)

Quatrix said:


> 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
> 
> ...


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.


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## Quatrix (Jan 1, 2020)

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


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## Quatrix (Jan 2, 2020)

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.


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## Michael Armstrong (Jan 2, 2020)

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.


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## afjes_2016 (Jan 3, 2020)

"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".


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