2 wire at ceiling , 4 wire and 2 breakers at breaker box.

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Old 12-08-17, 08:10 PM
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2 wire at ceiling , 4 wire and 2 breakers at breaker box.

i had a short, breaker would not reset.
went to look for the short, it is that old BX , the insulation crumbles when you move the wires.
decided to replace all of the old BX on that circuit with Romex, rather then creating more shorts while looking for this one.
trace the wire from the breaker to the BX entering the breaker box, and it is newer BX and it is 4 wire.
a red goes to a separate breaker on a separate circuit and a black goes to the breaker for the circuit i am working on.
an addition was done to the house years ago, i assume, originally, the circuit with the short went straight to the breaker and was two wire and the electrician that did the addition changed it to this.
my questions are, is this normal, can i leave it this way, or should i remove this 4wire and go with two separate circuits?
also, any easy way to figure out where, behind the walls, they would have connected the old 2 wire with the new 4 wire?
i assume at a light or switch, not just in the middle of a wall. just looking for any easy way to find it.
i can see the 4 wire from the breaker box to where it goes up into the wall in the basement and i can see the 2 wire from where it comes out of the wall in the ceiling .
the only way to see what happens behind the wall is to break through the drywall.
i am really hoping you are going to tell me this is normal and the 2 wire to 4 wire connection is in a light switch somewhere.
 
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Old 12-08-17, 08:26 PM
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Four wire is red, black, white and blue..... possibly green if MC lite.
Three wire is red, black, white...... possibly green if MC lite.
 
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Old 12-08-17, 09:19 PM
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Originally Posted by PJmax View Post
Four wire is red, black, white and blue..... possibly green if MC lite.
Three wire is red, black, white...... possibly green if MC lite.
i thought i saw 2 white, 1 black, 1 red.
i know i saw 1 black and 1red, as they come from the breakers and are easy to trace.
i did not see a blue or a green, so i will guess it is 3 wire.
black , white and red.
i have not pulled the wire out of the box yet, so it is hard to tell.
i know the other end, at the light fixture, is 2 wire, 14gage, old style BX. doesnt have a separate ground and the insulation crumbles off the wire when you touch it.
i already pulled that out of the wall. my intention was to use that as a snake to pull the new romex through into the basement.
but then i found a different wire on the other end.
 
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Old 12-08-17, 09:29 PM
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Since there is no visible ground.... you have old style cloth BX.

When you have white, black and red coming from a panel that means you have a MWBC (multi wire branch circuit). Two circuits sharing a common neutral. This takes special considerations. That wire must be connected to two breakers...... one above the other. Red must be on one leg and black must be on the other leg. It should connect to a 2P15A breaker or two single 15A breakers with a common tie handle.

Since they share a common neutral..... if you were to only shut off one circuit and opened the neutral.... you would get shocked. At some point..... that three wire cable needs to split to 2) two wire cables. At that location.... it is imperative that the neutral connection be well made. If that connection were to open.... you could get up to 240v on one of the legs.
 
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Old 12-09-17, 12:03 AM
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Originally Posted by PJmax View Post
Since there is no visible ground.... you have old style cloth BX.

When you have white, black and red coming from a panel that means you have a MWBC (multi wire branch circuit). Two circuits sharing a common neutral. This takes special considerations. That wire must be connected to two breakers...... one above the other. Red must be on one leg and black must be on the other leg. It should connect to a 2P15A breaker or two single 15A breakers with a common tie handle.

Since they share a common neutral..... if you were to only shut off one circuit and opened the neutral.... you would get shocked. At some point..... that three wire cable needs to split to 2) two wire cables. At that location.... it is imperative that the neutral connection be well made. If that connection were to open.... you could get up to 240v on one of the legs.
it is two breakers, not next to each other.
i have two rows of breakers, side by side.
1 of these two breakers is on the left, the other on the right. 1 is, if i recall correctly, three spaces higher then the other one.

looking at where this wire goes, which is through the addition to get to the older part, with the old BX, i am going to guess the new electrician didnt want to mess with the old BX either . he found a spot where the old BX was not broken and ran the new three wire to it.
the question now is, since i am replacing the old BX anyway, should i separate these two circuits?
leave the existing three wire there, remove the red and leave disconnected, connect the black to the breaker and to the branch line i am not replacing, then run new romex to the other breaker?
my other option is new romex to the existing branch, leave the existing 3 wire the way it is.
my thinking is, i no longer need the branch circuit because i am replacing the old BX. i can run new romex all the way to the breaker.
the problem with leaving it the way it is, i will have new grounded romex and new grounded outlets, connected to old BX that only uses the BX sheath as a ground.
why not replace the BX to the breaker and have all brand new, up to code, wiring and outlets?
i am also assuming the old 2 wire BX and the newer 3 wire BX , meet in the middle of the wall somewhere.
 
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Old 12-12-17, 07:08 PM
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i traced the wires.
the three wire from the panel goes to a junction box in the middle of a wall. there it joins two old style, 2 wire, BX cables.
i am still assuming the electrician did this as the easiest way to not mess with the old style BX cables.
so, my only question now is, can i remove this MWBC? is there any reason why i still need it?
cant i just replace all of the old style BX? remove the three wire and run two new 2 wires?
i already have two breakers and two separate circuits and i assume the electrician only did the MWBC because he didn't want to touch the old style BX.
and bonus,i finally fgured out why i have a box in the middle of a wall with a blank cover plate.
 
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Old 12-13-17, 09:45 PM
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cant i just replace all of the old style BX? remove the three wire and run two new 2 wires?
Absolutely. That's what I recommend.
 
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Old 12-14-17, 12:04 PM
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Originally Posted by PJmax View Post
Absolutely. That's what I recommend.
thanks, that is what i assumed, just wanted to make sure the electrician did the MWBC as a way to connect his new wring to the existing old style BX and there wasnt a reason why i still needed the MWBC.
 
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Old 12-14-17, 12:16 PM
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A MWBC is a way of getting two circuits to one area with a single cable. I very rarely will use one. Usually the only place I consider using them is in a kitchen for the countertop receptacles.
 
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