How do I identify multi-wired circuits?

[Spacecoastz]

During a power outage, I want to feed my house wiring (both legs) 120V, same phase. On the house I have an four-pin inlet box with breaker (to feed both legs), an interlock device on the panel, and an adapter cord that converts the TT-30 generator outlet to a L14-30 feed. What I'm concerned about are multi-wired circuits when both legs are on the some phase. Looking into the sub panel which contains most of the breakers I see four red wires that feed 120v breakers/circuits....all the others wires going into 120v breakers are black. Also, if every circuit had its own dedicated neutral, I have determined that there would be four more neutral wires.
All the individual 120v circuits that have red wires are associated with the kitchen.
The first circuit with the red lead powers two kitchen wall outlets...then the next circuit is the microwave which uses black into the breaker. All on the same wall.
Then a red lead that powers a different kitchen wall outlet next to the refrigerator....then the next circuit is the refrigerator using black into the breaker.
Then a red lead that powers an outlet on a kitchen island...then the next circuit is the dishwasher using black.
Then a red lead that powers a few family room outlets/closet light on one wall...then the next circuit feeds a family room wall using black.

Are those the multi-wire circuits that share a neutral? And if I simply throw the breakers off that use the red leads, I should be good when using the generator? Is there a way to determine for sure what two circuits share a neutral?

 

[Spacecoastz]

And yes, my generator does not have a 240v four pin outlet, plus with it being only 3,500 watt capacity I would think it would be easier to manage total demand, rather than both demand and each 120v leg. Thanks for any help.

 

[mike93lx]

A MWBC will have a 2 pole breaker that feeds 120v items.

Sounds like you have a bunch

 

[sparky 1971]

During a power outage, I want to feed my house wiring (both legs) 120V, same phase. On the house I have an four-pin inlet box with breaker (to feed both legs), an interlock device on the panel, and an adapter cord that converts the TT-30 generator outlet to a L14-30 feed. What I'm concerned about are multi-wired circuits when both legs are on the some phase. Looking into the sub panel which contains most of the breakers I see four red wires that feed 120v breakers/circuits....all the others wires going into 120v breakers are black. Also, if every circuit had its own dedicated neutral, I have determined that there would be four more neutral wires.
All the individual 120v circuits that have red wires are associated with the kitchen.
The first circuit with the red lead powers two kitchen wall outlets...then the next circuit is the microwave which uses black into the breaker. All on the same wall.
Then a red lead that powers a different kitchen wall outlet next to the refrigerator....then the next circuit is the refrigerator using black into the breaker.
Then a red lead that powers an outlet on a kitchen island...then the next circuit is the dishwasher using black.
Then a red lead that powers a few family room outlets/closet light on one wall...then the next circuit feeds a family room wall using black.

Are those the multi-wire circuits that share a neutral? And if I simply throw the breakers off that use the red leads, I should be good when using the generator? Is there a way to determine for sure what two circuits share a neutral?

The red wires are probably the second circuit of the MWBC. It should share the neutral with the black wire that is either above or below it. Follow the red wire to where it comes in and find the black that is in the same cable. Easy as that. Newer installations require breakers for MWBC's to either be two pole or connected via a handle tie.

 

[sparky 1971]

A MWBC will have a 2 pole breaker that feeds 120v items.

Sounds like you have a bunch

Not if it's old enough. The handle tie/two pole breaker rule went into effect with the 2008 NEC. I use handle ties on mine to eliminate the common trip.

 

[Spacecoastz]

It will? Every one of those that I mentioned have their own single pole individual breaker. There are individual breakers for : kitchen wall outlets below microwave....the microwave....kitchen wall outlet next to the refrigerator....the refrigerator.....kitchen island outlet....the dishwasher....family room outlets/closet light on one wall....and family room outlets on another wall. Eight circuits, each one having its own individual circuit breaker....thus eight individual breakers for what I just listed.

But out of those eight circuits I see four red wires going from four individual 120v breakers.

Are these not multi-wired circuits....where two circuits might be sharing a common neutral...but using the hot black for one circuit and the hot red for the other circuit?

The only two-pole breakers I have are for 240v appliances.

 

[mike93lx]

Not if it's old enough. The handle tie/two pole breaker rule went into effect with the 2008 NEC. I use handle ties on mine to eliminate the common trip.

Noted, thanks.

 

[sparky 1971]

It will? Every one of those that I mentioned have their own single pole individual breaker. There are individual breakers for : kitchen wall outlets below microwave....the microwave....kitchen wall outlet next to the refrigerator....the refrigerator.....kitchen island outlet....the dishwasher....family room outlets/closet light on one wall....and family room outlets on another wall. Eight circuits, each one having its own individual circuit breaker....thus eight individual breakers for what I just listed.

If it was wired prior to the 2008 code it probably won't have two pole breakers or handle ties. Those are all more than likely MWBC's.

 

[Spacecoastz]

Not if it's old enough. The handle tie/two pole breaker rule went into effect with the 2008 NEC. I use handle ties on mine to eliminate the common trip.

I think I understand. Most likely the circuits that are close together share the common neutral. I don't see any other 120v breakers using a red lead, so the kitchen/family room must be the only occurrence. House was built in 2001.

 

[Spacecoastz]

So...in using the generator as long as I don't use (or turn off one of the breakers) of each MWBC it would be ok...correct? I would not overload the neutral. The only real issue I see is that the toaster uses an outlet that probably shares the neutral with the microwave. So for sure I need to turn one of those off or not use.

 

[sparky 1971]

They should be close together, but who knows what someone else has done. Follow the red to where it enters the panel. The black that is in the same cable will be the other circuit. Then you will know.

 

[Spacecoastz]

They should be close together, but who knows what someone else has done. Follow the red to where it enters the panel. The black that is in the same cable will be the other circuit. Then you will know.

Got it....thanks.

 

[sparky 1971]

So...in using the generator as long as I don't use (or turn off one of the breakers) of each MWBC it would be ok...correct? I would not overload the neutral. The only real issue I see is that the toaster uses an outlet that probably shares the neutral with the microwave. So for sure I need to turn one of those off or not use.

The odds of winning the lottery are better than overloading the neutral with a 3500 watt generator.

 

[Spacecoastz]

Yeah...the only true issue is that most likely the toaster and microwave are on the same MWBC. Microwave is 1,700 watts alone...14 amps. If the toaster was operated at the same time (kind of likely) then that could overload the shared neutral. One will have to be off for sure. But like you said....I need to find out what is connected.

Edit...meant to say "unlikely".

 

[sparky 1971]

Yeah...the only true issue is that most likely the toaster and microwave are on the same MWBC. Microwave is 1,700 watts alone...14 amps. If the toaster was operated at the same time (kind of likely) then that could overload the shared neutral. One will have to be off for sure. But like you said....I need to find out what is connected.

You'll probably have other things on in the house at the same time as the toaster and microwave causing the generator breaker to trip if you use both at the same time. And, neither one is going to run for more than a couple of minutes, that's not long enough to cause catastrophic failure.

 

[nadogail]

Yeah...the only true issue is that most likely the toaster and microwave are on the same MWBC. Microwave is 1,700 watts alone...14 amps. If the toaster was operated at the same time (kind of likely) then that could overload the shared neutral. One will have to be off for sure. But like you said....I need to find out what is connected.

If your toaster and microwave are fed on separate phases the Neutral Currents might cancel out.

 

[mike93lx]

If your toaster and microwave are fed on separate phases the Neutral Currents might cancel out.

It's a 120v generator that he's trying to run. Just one leg

 

[Spacecoastz]

Looking in my panel the wires are really bundled and tied together. Really hard to see what black/red wires are coming from the same cable. Any other ways to determine what shares the neutral?

 

[mike93lx]

Looking in my panel the wires are really bundled and tied together. Really hard to see what black/red wires are coming from the same cable. Any other ways to determine what shares the neutral?

Just need to get digging and do some labeling. Can you share some pics of the panel?

 

[Spacecoastz]

Here. The ones I'm talking about are all on the right side of the panel. Any other red wires deal with 240V appliances. Look at the last photo....starting from the bottom the last red 120v is smaller gauge, same gauge as the black lead above it, vs the other thicker gauge wires that are above those two. Also those two are 15 amp breakers where as the others above them are 20 amp. The black operates family room outlets on one wall...the red lead operates family room outlets/ceiling lights on a different wall. I would think those two share the common neutral. Really hate to dig into these nicely arranged wires.

 

[mike93lx]

That is incredibly neat and would be very easy to trace.

Buying some colored zip ties might help. Clip the existing ties and place a new zip.tie on the wire you want to trace, at the breaker. Slide it along, all the way to the exit. Should take a few minutes. Personally, I would just clip the zip ties, pull the bundle apart a little and trace it

 

[sparky 1971]

Those are just a bunch of wires to everyone looking at the pictures. Cut the zip ties that are bundling everything together so you can trace the wires. You are making this way too difficult and are concerned about something that won't be a problem.

 

[sparky 1971]

.

 

[sparky 1971]

That is incredibly neat and would be very easy to trace.

Buying some colored zip ties might help. Clip the existing ties and place a new zip.tie on the wire you want to trace, at the breaker. Slide it along, all the way to the exit. Should take a few minutes. Personally, I would just clip the zip ties, pull the bundle apart a little and trace it

You beat me to it. Some people can turn the simplest of projects into a task more monumental than building the Hoover dam.

 

[mike93lx]

You beat me to it. Some people can turn the simplest of projects into a task more monumental than building the Hoover dam.

Yeah, I was expecting a dumpster fire but it's just about the neatest panel I've seen

 

[Spacecoastz]

I guess that part of my issue....I hate messing with something so neat. Not trying to make simple into difficult, but the issue of mwbc is new to me so I want to be sure I don't do anything stupid when using a generator and creating a single phase into the house. Thanks for the help everyone...appreciate it.

 

[Jlanciani]

Removed, I missed a piece in the OP.

 

[mike93lx]

I guess that part of my issue....I hate messing with something so neat. Not trying to make simple into difficult, but the issue of mwbc is new to me so I want to be sure I don't do anything stupid when using a generator and creating a single phase into the house. Thanks for the help everyone...appreciate it.

I get the apprehension. Just go for it. Be slow, be careful. No need to blow it up.

Just remember that the two center lugs on the top are unfused and always live. Stay away from them and putting a cover over, like a piece of cardboard, might be prudent

 

[Sumboodie]

I guess that part of my issue....I hate messing with something so neat. Not trying to make simple into difficult, but the issue of mwbc is new to me so I want to be sure I don't do anything stupid when using a generator and creating a single phase into the house. Thanks for the help everyone...appreciate it.

Your house is 3 phase?

 

[wyliesdiesels]

I get the apprehension. Just go for it. Be slow, be careful. No need to blow it up.

Just remember that the two center lugs on the top are unfused and always live. Stay away from them and putting a cover over, like a piece of cardboard, might be prudent

This has to be a subpanel. 4-wire feeder, Neutral not bonded, no main breaker...so he could turn off the power upstream...

 

[mike93lx]

This has to be a subpanel. 4-wire feeder, Neutral not bonded, no main breaker...so he could turn off the power upstream...

Great point

 

[yatg]

This has to be a subpanel. 4-wire feeder, Neutral not bonded, no main breaker...so he could turn off the power upstream...

but the bonding screw appears to be installed.
(green screw at bottom of left bar)

 

[mike93lx]

but the bonding screw appears to be installed.
(green screw at bottom of left bar)

That's a ground bar. It should be bonded.

It's the neutral (on the right) that shouldn't be bonded in a sub

 

[wyliesdiesels]

but the bonding screw appears to be installed.
(green screw at bottom of left bar)

Left bar is the ground bar not the neutral bar

 

[yatg]

Left bar is the ground bar not the neutral bar

ugh. need more coffee.

 

[Norcal]

The panel is a cheapskate special, full of twin breakers, too cheap to buy a ground bar kit, so they repurpose one side if the split neutral as a ground bar, use anti-short instead of Romex connectors, at least it appears that they used the bonding screw on the site hacked ground bar, not everyone does that.

 

[Spacecoastz]

This is a sub-panel in the garage. My house is fairly big...so the disconnect main panel is on the other side of the house (outside) with the main disconnect. It also has circuits, including running the pool pump/equipment, but no red wires for any of the 120v circuits. I clearly see that the ground bus bar and the neutral bus bar in the MAIN panel is bonded...which is how it should be.

I'm going to do either one of two things to give me peace of mind...either I'll trace back the red leads to determine the other black lead within the cable, thus making the mwbc, or I'll just switch off (during generator usage) the breakers that have the adjourning blacks. Fortunately those are just kitchen counter outlets and a family room wall that the tv is not on. The refrigator breaker runs off a red lead, the microwave runs off a red lead, the island outlet runs off a red lead, and the F/R tv wall outlets run off a red lead. If I understand this correctly, none of them could be sharing the same mwbc. It would be helpful to stay on topic....I'm trying to deal with this mwbc's when using a generator that will make 120v single phase. Thanks.

 

[AntonLargiader]

If those are twin or slim breakers as Norcal pointed out, make sure the MWBCs actually are on different stabs. Seems to me you could get that part wrong.

 

[Spacecoastz]

If those are twin or slim breakers as Norcal pointed out, make sure the MWBCs actually are on different stabs. Seems to me you could get that part wrong.

If that was the situation, then I would have a potential problem now....generator usage or not. Correct? I think every other breaker uses a different leg.

 

[mike93lx]

If that was the situation, then I would have a potential problem now....generator usage or not. Correct? I think every other breaker uses a different leg.

Slim breakers have two breakers per leg. So each pair would be together.

So if you take the right side, top to bottom and number the breakers starting at one, with full size breakers, 1, 3, 5, etc would be on the same leg. With tandem (half size), 1, 2, 5, 6, 9, 10, etc would be on tbe same leg. So a MWBC would need to go on 2 and 3 instead of 1 and 2 or 3 and 4