Calling all electricians- Sharing neutral on split wired circuit ?

[David Ruhland]

I swear I asked this question once already, but I can’t find it. Dam old age...

If I run a new 20 amp duplex outlet and want it to be two separate circuits ( split wired) can I share the neutral? ( have lots of leftover 12-3 w/grd) if so is this code?

Outlet will most likely be used simultaneously with a table saw and dust collector

thx

[Jason Roehl]

There is one "exception" in the code that allows this--the two circuits in question must be on adjacent, bonded breakers (one trips, they both trip) that are on different legs of your electrical service.

[David Ruhland]

There is one "exception" in the code that allows this--the two circuits in question must be on adjacent, bonded breakers (one trips, they both trip) that are on different legs of your electrical service.

LIGHTBULB MOMENT! Now i understand why i have seen a piece of wire through breakers in a panel from time to time! I thought someone was just trying to make their own 220 breaker! Thanks....

[Dick Mahany]

There is one "exception" in the code that allows this--the two circuits in question must be on adjacent, bonded breakers (one trips, they both trip) that are on different legs of your electrical service.

My builder did this in my new home (built 2016). It has been a terrible idea. The bonded breaker circuits involved are the outlets on one breaker and overhead lights on the other. Unfortunately, these are both in my garage/shop and I found out the hard way when I tripped the outlet breaker with my portable table saw and immediately lost all of the lights. Really scary as there are no windows in the garage and it went totally dark with the blade spinning down. To make it worse, the outlets are on a GFCI and seem to be more temperamental than a standard outlet.

I have since added separate circuits for power tools to avoid this in the future.

If you decide to share the neutral, be sure not to have lights and outlets together on those bonded breakers.

[David Ruhland]

Good Point Dick! I had that happen once too... scary as hell..

I was only wondering cause i have a bunch of 12-3 wire w ground a guy gave me... The one outlet w 2 circuits is going to be direct from my elec panel to the location of my saw and dust collector so i should be alright.

Thanks again for the advice...

D

[Paul F Franklin]

I prefer to use a double pole breaker rather than two singles with a handle tie....more difficult for a clueless someone in future to undo the handle tie, but either way meets code.

As Dick referred to in passing, if this is an area that requires GFCI or AFCI protection, then you have to use a two pole GFCI or AFCI breaker because two singles won't work with a shared neutral.

And I completely agree with Dick that lighting and receptacles should be kept separate.

[Jim Becker]

My builder did this in my new home (built 2016). It has been a terrible idea. The bonded breaker circuits involved are the outlets on one breaker and overhead lights on the other. Unfortunately, these are both in my garage/shop and I found out the hard way when I tripped the outlet breaker with my portable table saw and immediately lost all of the lights. Really scary as there are no windows in the garage and it went totally dark with the blade spinning down. To make it worse, the outlets are on a GCFI and seem to be more temperamental than a standard outlet.

I have since added separate circuits for power tools to avoid this in the future.

If you decide to share the neutral, be sure not to have lights and outlets together on those bonded breakers.

Clearly, the best practice if one decides to use this method for split wiring these outlets with separate circuits would be for the two circuits to share the double pole breaker/bonded side-by-side breakers. I'm not sure I'd do this personally, but that's because I just plain would not prefer to have a shared neutral. I agree that lighting should always be isolated from the general outlet population, especially in a shop!

[David Ruhland]

I'm not sure I'd do this personally, but that's because I just plain would not prefer to have a shared neutral

Jim, my wife says i am selfish and dont like to share (esp when it comes to my tools) so im gonna keep it real simple and simply pull two 12/2 w grounds! Thanks for all the great info here...

[Jim Becker]

Dave, you could still use the 12/3+G if you have a lot of it and don't want to spend money for more wire. Just cap off the "red" conductor for "future" use.

[Wade Lippman]

Outlet will most likely be used simultaneously with a table saw and dust collector

thx

Both are high current devices and will be used at the same time. You will have less voltage drop with a multiwire circuit.

[Tim Bridge]

I prefer to use a double pole breaker rather than two singles with a handle tie....more difficult for a clueless someone in future to undo the handle tie, but either way meets code.

As Dick referred to in passing, if this is an area that requires GFCI or AFCI protection, then you have to use a two pole GFCI or AFCI breaker because two singles won't work with a shared neutral.

And I completely agree with Dick that lighting and receptacles should be kept separate.

When you use a double pole breaker, both poles will trip at the same time if either circuit gets overload.

If you use single pole breakers with a handle tie, then only the overloaded circuit will trip.

Double pole breakers have a common internal trip unit.
When breakers are connected together with handle ties, one can trip because they are “trip free” and can still trip if held in the on position.

[Jim Becker]

Outlet will most likely be used simultaneously with a table saw and dust collector

I inadvertently missed that...no way would I do a shared neutral for two high loads like that.

[Rollie Meyers]

I inadvertently missed that...no way would I do a shared neutral for two high loads like that.

It is not a issue to have a common neutral, unless both shared the same leg then the neutral could become overloaded.

[Art Mann]

I know it is not intuitive but Jim and Rollie are both quite mistaken and Wade is correct. If the load on both legs is the same then zero current will flow in the neutral wire, even at full load. The worst case is that full load current from one leg will flow in the neutral wire and that is only if the other leg is completely unloaded.

[Bruce Wrenn]

Go to the NEC and look up multi wire branch circuits. The feed to your house is a multiwire circuit. The two hots share a single neutral. As for tie bars for the breaker, these have to be furnished by the manufacturer of the breaker.