Lights on Common Neutral

[gsmittle]

I need to tap the collective wisdom: I'm installing two lighting circuits in my shop, one upstairs and one on the main floor. Both switches are in the same box. The circuits are on two different breakers, and I'm wondering if I can use a common neutral for the two circuits. They are on different halves of the 220.

Hope that makes sense…

g.

[eccentrictinkerer]

Tech-wise, it'll work.

Code-wise, nope.

[woodturner]

The circuits are on two different breakers, and I'm wondering if I can use a common neutral for the two circuits. They are on different halves of the 220.

Only if it meets the specific exceptions in NEC that allow for a split neutral. Unfortunately, I don't have my code book in front of me and can't look up those exceptions at the moment.

[tfischer]

I'm not an electrician but I believe this is allowed IF you use a double pole breaker rather than two single breakers. Otherwise someone in the future could rearrange the panel and put them on the same phase which would be a fire hazard.

[eccentrictinkerer]

Some idiot* wired an outlet in my kitchen... single neutral and one of each phase to each of the two outlets on the receptacle. Separate breakers to each outlet. Thought the outlet was dead.

I shut off the breaker I thought fed the outlet. Went in to do some rewiring and screwdriver touched a terminal to ground. 20 amps takes a big bite out of a screwdriver.

Wiring as described in your OP is code in very specific instances, but considered bad practice by many. (If you do it make sure you use a double breaker).

* The idiot was me, done 20 years before.

[woodturner]

Some idiot* wired an outlet in my kitchen... single neutral and one of each phase to each of the two outlets on the receptacle.

That is one of the "legal" exceptions, as I recall.

Wiring as described in your OP is code in very specific instances, but considered bad practice by many.

Definitely agree it is not good practice.

[JSUPreston]

I shut off the breaker I thought fed the outlet. Went in to do some rewiring and screwdriver touched a terminal to ground. 20 amps takes a big bite out of a screwdriver.

I have a friend who used to work for Wang Global in the 70's-80's. He did that inside a laser printer...once! He said when he found the nut driver, there was so little metal holding it together that he had to throw it away.

[BigguyZ]

I'll confirm what's been said. shared neutral allowed if a tandem breaker is used (or is there's a bridging bar installed that makes two breakers a tandem breaker.

However, I don't think it's a good practice and would rather run two separate lines all together.

[gsmittle]

Thanks for the replies, guys. I was thinking that since both neutrals went to the same neutral bus inside the panel, I'd be OK with one neutral wire. Running one more conductor is a piece of cake.

I got the idea from the electrician who installed my panel; he wired a box with four GFCIs, two on each circuit with a common neutral. The GFCIs have little LEDs to tell me if they're hot.

g.

[Stytooner]

It's actually harder for me not to run a separate neutral I think.
I have my wire in a make shift caddy for rolling them out. It all works great if all three spools are turning. IE black, white and green. It would still work if I didn't pull a white. However these were all equal size rolls to start with. Why not pull a white with it?

[tfischer]

The only time I've ever done this was when we needed power to our garage/shop when we first moved here. The existing garage had one circuit that was shared with the living room of the house... not exactly ideal for running power tools, etc. The easiest way to get power there (the panel was on the far side of the house) was to use an existing conduit which had capacity for 3 new wires but not 4. So I added a 20A shared neutral circuit. A few years later I added a new subpanel to the garage giving me a few more circuits that don't use the shared neutral and those are now my "primary" circuits although the shared neutral ones are still in use too.