WIring Help, 2 circuits wired together red to black


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Old 12-07-22, 11:14 PM
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WIring Help, 2 circuits wired together red to black

Hello everyone. thanks for reading this.
I am trying to install a timer for my porch lights and a dimmer switch for my foyer chandelier. Both are fairly straightforward but when I opened my multi-gang box I could not get all the power off. I opened the circuit for the foyer and that dropped the current from 122V to 49V. I realized that there is a black from the living room circuit connected to the red from the foyer circuit. When I open the living room circuit everything goes to <0.2V.

Why would the black from one breaker be connected to the red of another breaker?
All the neutrals from both circuits are also wired together.
How would I correct this?

Thanks again to anyone taking the time.


Wiring for porch and chandelier switch with the black and red of different circuits connected

Wiring schematic for porch and chandelier switch with the black and red of different circuits connected


breaker panel
 

Last edited by DrFeelGood; 12-08-22 at 12:57 AM. Reason: added image
  #2  
Old 12-08-22, 01:36 AM
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Two circuits sharing a neutral would be a MWBC (multiwire branch circuit). Google it for a full explanation of how they are formed and what they are used for.

B#1 seems to be the MWBC. It should be a two pole breaker or two single pole breakers one on top of the other tied together with a pin at the handles.

Are you sure B#2 is a breaker?. Would seem it is just feeding another cable.

The two switches are being fed by B#!.
3 way chand and single pole porch (no such thing as a 2 way).

I would double check to see if cable #2 is connected to a breaker.

If #2 is a breaker it should not be connected to neutral or hot from B#1. B#1 if is a MWBc is sharing its neutral from the 2 pole breaker it is connected to which is fine but should not be connected to the neutral of B#2 which could overload the neutral.

If B#2 is a breaker I would disconnect the red and black and wire nut them separately and disconnect the white neutrals. Wire nut the white neutrals as B#1 whites together and cap off the white neutral from B#2.

It's still early in the morning for me and I am running on 1/2 cup of coffee but if B#2 is a breaker I don't see why it would be connected to B#1 which should be a two pole breaker. It would seem that what you show as B#2 is a feed from B#1 going somewhere else and not power coming into the box from B#2.

Someone else please double check me here.

If the red from B#1 and the black from B#2 (that is if B#2 is a breaker) and they are on opposite legs then black and red will give you two hots of 240v

Something just is not right here.


It also looks as though someone used two tandems to create mWBCs. No tie bars and also not the right way to do it. A MWBC should be to a two pole or two single poles connected together with a tie bar.
 
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Old 12-08-22, 08:17 AM
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How did you determine the connected black and red come from two different breakers? I think you have misidentified the wiring. The 49v reading you are seeing could be phantom voltage and is also confusing things for you. I assume you are using a digital multimeter.
 
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Old 12-08-22, 04:52 PM
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It's not how the mwbc is used. It is two distinct circuits sharing a common neutral.
The problem is when only one breaker gets opened and then the neutral is worked on.
Once the neutral opens the second circuit feeds back thru the first circuit.

Code has demanded that either a 2P breaker be used or 2) single pole breakers with a handle tie.
It is desirable to have both circuits disconnected when either one is being worked on.

 
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Old 12-08-22, 10:23 AM
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For the discussion... it would be helpful to know how the panel is labeled.
If we assume every handle has its own number.... odds on the left.... 4th and 5th handles down.
#7 is red
#9 is black
Two tandem breakers.... no handles tied.
The panel has mostly MWBC's and no tie handles. That shouldn't have passed inspection.

That means the breaker 1 cable is the feed. (two circuits)
#7 red feeds power to what's labeled breaker 2.
#9 black feeds the lights.
 
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Old 12-08-22, 11:19 AM
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PJmax You nailed it!

Apologies pattenp AFJES I did not do my part and test fully.


The final verdict is as stated in #4 above "That means the breaker 1 cable is the feed. (two circuits) #7 red feeds power to what's labeled breaker 2. #9 black feeds the lights."



Diagram showing two circuits in one feed using a common neutral with red connected to black


This would mean that the 49v I detected originally along the "foyer" circuit 1 (above), after opening that breaker, was indeed "ghost current" as others have suggested from the closed circuit 2 "living" that was alongside.

Is the a code violation? It looks like a MWBC that uses a 3-wire to 2-wire.

Thanks everyone for your continued input.
 
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Old 12-10-22, 11:28 AM
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The requirements for a simultaneous disconnect came about after your house was built. Previously it was only required if both hots landed on the same yoke.
 
 

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