Contractor ran 14/3, 12/3 lines from basement - Can I use them?

[b-boy]

A few years ago I had some work done on my 2nd floor bathroom. The contractor needed to run 2 new dedicated circuits (1-15A, 1-20A) from the first floor to my attic. He then then dropped them down into the bathroom through the ceiling.

I knew I was going to be refinishing my attic in the future, so I asked him to run some extra cable that I could use for the attic upgrade. It's been a few years, and I've started working on the attic. I opened up the wall expecting to see unused 12/2 and 14/2 cables. Instead I found that he ran 12/3 and 14/3 through the attic and into the bathroom. He just capped off the red wires. I opened my electrical panel and sure enough, the red wires are in there.

If I use this for the attic, the neutral would be shared. The 15A will be 100% LED lights, and the 20A will have minimal usage (although I could see the possibility of a small window A/C being used). The 20A is also on the same circuit as my wife's hairdryer.

Any concerns about using this, or do I need to pull new cables?

 

[PCustoms]

What's the concern?

Is it wired MWBC?

 

[rlitman]

Do you have regular breakers or GFCI? So long as you don't have GFCI upstream (presumably at the panel), then you could use these as MWBC with a two-pole breaker or a handle-tie.

 

[dave*99]

If you have 4 open slots you can create 2 MWBC and effectively have (2) 15 A circuits and (2) 20 A circuits.

 

[dave*99]

Post a photo of the wires and breakers in the panel

 

[b-boy]

Yes. It will be wired MWBC. No GFCI upstream. My main concern was running a small A/C unit at the same time my wife fires off her monster, soul sucking hair dryer. Is that kosher?

Sounds like as long as the breakers are tied together, it's OK? I'm reworking the panel, but I might need to add a tandem breaker for the 20A circuit.

 

[dave*99]

Hair dryer and AC on separate sides of the MWBC are fine. Do not use a tandem breaker. It will overload the neutral.

The reason a MWBC works is because the red and black wires are out of phase and the neutral only carries the difference in current between the two. With a tandem breaker the neutral carries the sum.

 

[Norcal]

As long as the black, & red are on different legs in the panel, plus a handle tie is used connect both breaker handles, or use a 2 pole breaker all will be fine, and don't forget to update the circuit directory.

 

[rlitman]

Hair dryer and AC on separate sides of the MWBC are fine. Do not use a tandem breaker. It will overload the neutral.

The reason a MWBC works is because the red and black wires are out of phase and the neutral only carries the difference in current between the two. With a tandem breaker the neutral carries the sum.

For those not familiar with the terminology, a tandem breaker fits two breakers into one slot, but it still uses only one pole on the panel bus. For an MWBC to work, you need a breaker that connects black to one pole and red to the other (240V between the two), so that the neutral isn't overloaded. Ideally, with both circuits at capacity, the neutral actually sees no current at all.

Also, this sort of double tandem breaker WILL work, so long as the MWBC is the middle pair of wires.

 

[Zeke]

Yes. It will be wired MWBC. No GFCI upstream. My main concern was running a small A/C unit at the same time my wife fires off her monster, soul sucking hair dryer. Is that kosher?

Sounds like as long as the breakers are tied together, it's OK? I'm reworking the panel, but I might need to add a tandem breaker for the 20A circuit.

No, the soul sucking draws too much current.

 

[b-boy]

Thanks for the feedback on this.

Especially the explanation about the red and black wires needing to be out of phase. Now it makes perfect sense.

 

[Norcal]

For those not familiar with the terminology, a tandem breaker fits two breakers into one slot, but it still uses only one pole on the panel bus. For an MWBC to work, you need a breaker that connects black to one pole and red to the other (240V between the two), so that the neutral isn't overloaded. Ideally, with both circuits at capacity, the neutral actually sees no current at all.

Also, this sort of double tandem breaker WILL work, so long as the MWBC is the middle pair of wires.

That is a quad breaker, not a tandem/twin.

 

[thammel]

You know that MWBC will not allow for the use of arc fault breakers....in case you want to use these or need to.

 

[egdede]

I have siemens arc faults on my MWBC. They never nuisance trip. They are spendy though:

https://www.amazon.com/dp/B0052MD8AK/?tag=atomicindus08-20

 

[b-boy]

That is a quad breaker, not a tandem/twin.

I have an older Square D QO panel. I don't think I can get quads for that box. I'm going to have to do some rearranging to get everything working, but it won't be too bad. I have way too many circuits for what's actually in my house. I swear there are dedicated circuits supporting 1-2 outlets.

 

[rust in the eye]

The red should be connected to the opposite phase (on a separate breaker)as the other wire sharing the neutral.
You'll need to know the amps required of your window A/C to make the call. 20 amps is a lot but I could imagine a compressor starting while the wife is blow drying might get close.

 

[b-boy]

I'm having a weird experience with my recent electrical work.

I got everything hooked up today. I have 2 circuits in my attic. A 15A for lighting, and a 20A for outlets. I rand new circuits from the basement to a junction box in the attic. I've rewired the attic and hooked the new wiring into that junction box.

The lights have been working for a few weeks. I have 8 puck lights and a ceiling fan. The lights and fan have their own switches.

I finally finished the drywall and wired all the recepticles. I turned off power to the 20A circuit so I could make my final connections. I always test the circuit to see if it's live. I did that and I was surprised to see that the new circuit I was preparing to connect was live. The ground, neutral, and hot all lit up my tester. The circuit was not hooked up to anything. I went around the room and tested each recepticle. All of them beeped. I got my volt meter and tested them. They all showed no current. I tested each wire in the junction box, and the ground read 6 volts. On a hunch, I turned off the lights, and the problem disappeared. I turned them back on and it came back. I took the ground and touched it to the ground on the circuit I ran from the basement, and as soon as I did that, no more live wires.

The wiring for the lights takes the same path as the wiring for the recepticles. The wires run parallel to one another through the studs.. I built knee walls, so I was able to crawl behind the walls to see if there was a nail or screw that might have penetrated through the wires. There doesn't appear to be one.

I'm stumped. I know there can be crossover interference between communication wires, but I didn't think electrical wiring had the same issues.

Any idea what might be going on here?

 

[PCustoms]

I'm having a weird experience with my recent electrical work.

I got everything hooked up today. I have 2 circuits in my attic. A 15A for lighting, and a 20A for outlets. I rand new circuits from the basement to a junction box in the attic. I've rewired the attic and hooked the new wiring into that junction box.

The lights have been working for a few weeks. I have 8 puck lights and a ceiling fan. The lights and fan have their own switches.

I finally finished the drywall and wired all the receptacals. I turned off power to the 20A circuit so I could make my final connections. I always test the circuit to see if it's live. I did that and I was surprised to see that the circuit I was preparing to connect was live. The ground, neutral, and hot all lit up my tester. The circuit was not hooked up to anything. I went around the room and tested each receptacal. All of them beeped. I got my volt meter and tested them. They all showed no current. I tested each wire in the junction box, and the ground read 6 volts. On a hunch, I turned off the lights, and the problem disappeared. I turned them back on and it came back. I took the ground and touched it to the ground on the circuit I ran from the basement, and as soon as I did that, no more live wires.

The wiring for the lights takes the same path as the wiring for the receptacals. The wires run parallel to one another through the studs.. I built knee walls, so I was able to crawl behind the walls to see if there was a nail or screw that might have penetrated through the wires. There doesn't appear to be one.

I'm stumped. I know there can be crossover interference between communication wires, but I didn't think electrical wiring had the same issues.

Any idea what might be going on here?

Throw away your non contact tester and learn how to properly use your meter. Or call an electrician.

 

[b-boy]

I did use my meter. Just wondering where the 6 volts came from.

I assume it's just phantom voltage from the other wire. Just want to verify that.

 

[PCustoms]

I did use my meter. Just wondering where the 6 volts came from.

How did you use your meter to measure current in a potentially live circuit?

 

[b-boy]

I touched the ground from the new wire to the ground of the wire I wanted to connect to. The breaker was off, so there was no current. I got 6 volts. I was pretty sure the new wire wasn't really live because I had been working with it all day.

 

[MovingAlong]

I'm having a weird experience with my recent electrical work.

You can start with the assumption that something was done incorrectly. Electrical work doesn't act "weird"... There is a reason for the behaviors you're seeing.

I got everything hooked up today. I have 2 circuits in my attic. A 15A for lighting, and a 20A for outlets. I rand new circuits from the basement to a junction box in the attic. I've rewired the attic and hooked the new wiring into that junction box.

You mention two circuits but only one junction box. Do you have both circuits sharing one box? Are you certain you kept the hot/neutral/grounds properly separated?

The lights have been working for a few weeks. I have 8 puck lights and a ceiling fan. The lights and fan have their own switches.

I finally finished the drywall and wired all the recepticles. I turned off power to the 20A circuit so I could make my final connections. I always test the circuit to see if it's live. I did that and I was surprised to see that the new circuit I was preparing to connect was live. The ground, neutral, and hot all lit up my tester. The circuit was not hooked up to anything. I went around the room and tested each recepticle. All of them beeped. I got my volt meter and tested them. They all showed no current. I tested each wire in the junction box, and the ground read 6 volts. On a hunch, I turned off the lights, and the problem disappeared. I turned them back on and it came back. I took the ground and touched it to the ground on the circuit I ran from the basement, and as soon as I did that, no more live wires.

I'm not an electrician but thought the ground wires would be bonded by the junction box anyways...

The wiring for the lights takes the same path as the wiring for the recepticles. The wires run parallel to one another through the studs..

Different circuits run parallel in and out of the panel box too... don't believe that is your problem.

I built knee walls, so I was able to crawl behind the walls to see if there was a nail or screw that might have penetrated through the wires. There doesn't appear to be one.

I'm stumped. I know there can be crossover interference between communication wires, but I didn't think electrical wiring had the same issues.

Any idea what might be going on here?

One of the challenges is how you're making and reporting your measurements. You mention using a volt meter on a circuit with no load and say "they all showed no current". Typically you would only see current with a load... Voltage sure, but current?

You mention measuring 6 volts on ground. It takes two leads to measure voltage, what was the other lead connected to if not ground?

My suspicion is that you've either mixed or combined the wiring improperly between the two circuits in your single junction box. But hard to tell from here... Pictures of the panel box, breaker, junction box and a wiring diagram would all be helpful.

Wishing you only success!

 

[dave*99]

I touched the ground from the new wire to the ground of the wire I wanted to connect to. The breaker was off, so there was no current. I got 6 volts. I was pretty sure the new wire wasn't really live because I had been working with it all day.

You have multiple ground wires all in the same box and they are not all connected together?
Why is that?

 

[BOONEY7750]

If you have 4 open slots you can create 2 MWBC and effectively have (2) 15 A circuits and (2) 20 A circuits.

I like this idea.

 

[b-boy]

Sorry if I'm not being clear.

I have 2 home run circuits that were run by a contractor to my attic from the basement. There is a 14/3 and a 12/3. They are separate. The circuits were run, but not connected at the panel. That's been done now. There is power from the panel to the junction boxes. I

I have wired the attic. I have 1 circuit for lighting (15A) and 1 for outlets (20A). n this situation, the 20A circuit was turned off at the panel.

The lighting circuit has been up and working for several weeks. No problems.

The attic outlet circuit was run, but had not been connected to the wiring from the panel in the junction box. I needed to finish drywall and add the receptacles. That's been completed.

The last step was to connect the wiring from the receptacles to the junction box with the 20A circuit from the panel. All had to do was wire nut the 2 sets of wires together.

That's when I encountered the 'live' wire condition. My wire tester beeped when I got near the new wiring, even though it was not connected yet. I had previously touched the wire, so I was pretty sure it wasn't live. I used my tester to see if the outlets were live. I got a hit on every one. I got my multimeter and checked voltage across the outlets I got 0v. I used the multimeter and touched the ground wire in the junction box to the other ground wire. I got 6V.

This only occurs when the ceiling lights are turned on. I've checked for crossover between the circuits. I don't see anything.

I hope that's clearer.

 

[dave*99]

Check the 12/3 and 14/3 connections in the main panel.

If the ground wires from those are landed on the ground bus properly and there are no breaks in the cables, it hard to imagine how there can be 6 volts between 2 ground conductors in the attic that are properly connected to the same bus in the main panel.

A small voltage could appear from your lighting load current if you accidentally connected neutral to ground in your lights, but even that should not be as high as 6 volts.

 

[billconner]

And per Dave's direction, check grounds at the point the electrician ran the 12/3 and 14/3 to for ground continuity to your 12/2 andc14/2 that goes to attic.

I think maybe you should check the electricians work. Disconnect yours and check all devices.

 

[b-boy]

Thanks. I will look at the panel again.

 

[MovingAlong]

Thanks. I will look at the panel again. (And will take pictures this time, no really I will, promise...)

Looking forward to seeing the pics!

Ok, I may have taken some liberties with the quote - but pics really would help...