Simple electrical question

Thinking of wiring half of one of my outlets in my shop to turn
off with the lights. Leaving my battery charger for my cordless
tools plugged in scares me and forgetting to plug it in ticks me
off when I need a fresh battery.

I know I can run a single hot wire from a light box and to the
oultet and use the neutral as shared between the light
operated socket and the rest of the outlets. Since they are on
different legs any additional current run through the charger
would cancel the same amount of current running through the
other sockets in regard to the shared neutral (no worries of
overloading an unprotected neutral). My question is, if the
neutral were to somehow lose connection with the neutral bar
wouldn't that fry everything on that circuit? Essentially making
the lights 220v? Also, I am guessing that the low Earth
potential of the neutral keeps the power from back feeding the
hots and making them 220v, is that right?


Thanks!

Depends if the 2nd circuit is supplied from the same or opposite line. You could end up with 30 amps on a 15 amp neutral wire.
Still not completely certain what you are trying to accomplish?
Line 1 and line 2 are 180 degrees out of phase. That is why between L1 and L2 there is 240V. That is also why if L1 has a 12 amp 120V load and L2 has a 7 amp 120V load. The neutral which is an energized current carrying conductor.carries 5 amps back to the neutral bar and the transformer Center tap.

It is a common practice for two circuits to share a neutral, although a lot of electricians don't like it. An interesting characteristic of this "three wire" circuit is that if the loads are balanced between the two circuits, there is less voltage drop on both circuits than there would be if they had separate neutrals.

HOWEVER, your shop outlets should be GFCI protected, and GFCIs don't like three wire circuits. For this reason, the best way to do it is to run separate hot and cold wires to the switched outlet. You'll need to break both jumpers on the outlet so both hot and cold are separated. (I'm assuming that the switched outlet won't be GFCI'd, but all the other outlets should be on a GFCI.) Even if you don't have a GFCI now, doing it this way will keep you from going nuts if you install a GFCI circuit breaker at a future date.

I would just run a 2 wire from the light circuit to that outlet to be on the safe side.

Run 2 separate circuits, boxes and receptacles. Simpler, safer and you never have enough receptacles in a shop anyhow!
35 years ago I wired the kitchen in our new house that way,(as recommended by the inspector) but when we built our cabin 10 years ago I just put every other receptacle on a different breaker.

I know the proper way to do all this, its indeed SIMPLE (for an engineer or electrician) as you stated HOWEVER based on your question I don’t think you understand the concept of “shared neutral” when and how its permissible and safe, and what are known as “multi wire branch circuits” so my best professional advice is to seek trained professional electrician help. THAT BEING SAID HERE ARE A FEW TIPS

1) I NEVER mixed lighting branch circuits with convenience outlet branch circuits. Id have lighting branch circuits and Id have outlet branch circuits but NEVER both on the same.

2) Multi wire branch circuits are permissible but NOT for rookies or amateurs. On those you can (if all is done right) run a branch circuit consisting of 2 hots that share a common single neutral. If BOTH phase A and B were pulling 12 amps, the Neutral current would be zero.

3) Its NOT good to use multi wire circuits with high inductive loads like lighting ballasts and its NOT good to use a multi wire circuit where some loads are inductive and some are not because due to harmonic currents, the neutral may be overloaded

4) I suggest you DO NOT try to share Neutrals,,,,,,,DO NOT use a multi wire branch circuit if you don’t know what youre doing or what it is or how it works and when its permitted

5) I DO SUGGEST you run switched branch circuits complete with Neutral to the outlets you want controlled by a switch and run branch circuits out to outlets that are unswitched always hot and run separate branch lighting circuits AND DO NOT TRY TO SHARE NEUTRALS NOR USE MULTI WIRE BRANCH CIRCUITS unless and until you know exactly how to use them

CAUTION!!!!!!!!!!!!!! This is NOTTTTTTTTTTTTTTT one of those questions where you should rely on uneducated or ignorant lay opinions or rookies or jack legs or Billy Bobs !!!!!!! The concept of shared neutrals or multi wire branch circuits is NOT for rookies. DON’T TAKE MY WORD FOR IT see what trained professional electricians and engineers and electrical techs and the NEC has to say

YOUR 220 VOLT QUESTIONS: If the neutral was to open, the 120 volt loads that use that Neutral will not work. If theres a straight 240 volt load, it does NOT use Neutral so works without one. Its 120 volt from either hot to Neutral and 240 line to line.

Neutral is a live current carrying GrounDED Conductor,,,,,IT IS NOT THE EQUIPMENT GROUNDING CONDUCTOR. Never mix n match n substitute one for the other lest you get killed. Neutral is Neutral and Equipment Ground is Equipment Ground UNLIKE SOME ROOKIES THINK THEY Are notttttt the freaking same.

Im NOT trying to start a fight or argue, just giving the best professional advice to save a life or prevent a fire here. ALSO I cant explain how to do all this here in a few paragraphs, sorry

John T Retired electrical engineer

your best bet is to run a 3wire(blk red wht &grnd) nm or thhn, depending on your current wiring in your shop, from the light to the outlet. This is dependent on wether the circuit is in that box already, Switched and unswitched need to be at the light. once run to the outlet you could put in a double duplex(2outlets)run blk to unswitched outlet red to switched outlet, the neutral then is pigtailed to both outlets. gfci will work on unswitched just fine, but the switched one may be tricky. Some gfci's need to be reset when they loose power. If you can't install two seperate outlets, run the white to the neutral screw, break the tab between screws on the hot side. If you then want gfci protection, buy a corded gfci, for the unswitched side and try to us only battery charger in other. Is the light circuit, and it's wiring rated to operate the lights and outlets? good luck

John T is absolutely right except for one thing. Per the 2011 NEC, sharing a neutral is no longer permitted unless both "hot" legs are on a 2 pole breaker (or 3 pole in a 3 phase system). This is a change from prior years.
As a journeyman electrician, I agree with everything else John T advises, especially the part about seeking the help of a professional. I am not saying you are not competent or capable, just that this is the type of situation that can very easily become a shock or fire hazard if not properly installed.
A much easier suggestion might be to add a new switch near the existing one(s) and use it to control one or more outlets throughout the shop.
And yes, if you lose a neutral on a shared cricuit, you can put 240v across everything in the circuit.
Good Luck!
Jess

I'm no expert on wiring but I know that on some battery chargers if you leave them hooked up and the charger off, the batteries will discharge back through the charger. If it happens on tools, it might be hard on the batteries.

I don't think you can split a duplex outlet.

EXACTLY ,,,,,,,WE always used a 2 pole breaker even if it wasnt in the code THATS THE SAFE WAY TO DO IT and how we alwayssssssss did it (I sure never told anyone to use a single did I grrrrrrrr my bad if I told anyone that). I cant try to explain EVERY LITTLE DETAIL in my posts, heck Im already too long winded lol

Fun chat, thanks

John T

Its "mechanically" possible, (I NEVER did it, unsafe esp for rookies) thats why the tear off tie tabs can be broken on duplex receptacles. Problem is theres 240 available in that box plus if a two pole breaker wasnt used even if one leg off theres still 120 in there !!!!!!!!!

Multi wire branch circuits and shared neutrals are UNSAFE for rookies and amateurs use

Fun chat

John T

OK thanks John. Did not realize there were break-off tabs. But I still think I'd put another receptacle in a 2nd box. Those plastic boxes are so easy to work with. I'm not sure why the plastic boxes are even legal but they sell them just the same.

I agree, ID USE TWO SEPERATE OUTLETS AND BOXES where farmer Bob may be getting into those outlets I dont like BOTH hot legs being there and they may not have used a 2 pole breaker YIKES

You dont have to mess with grounding those plastic boxes is one advantage but if youre taking the devices in and out very often Id worry about the plastic threads...

Take care Nebraska

John T

If you really want to do something like this I would say you should isolate the circuit and use a relay to control the current to the outlets using the light circuit to energize the relay.

If your real ambitious you could run a subpanel and control several circuits with one contactor.

I have been wanting to do something like that with my air compressor but have never got around to it.

Seems like the neutral issue and such has been addressed here, but from a convenience perspective I suggest you just put the receptacles you want to switch on a separate circuit and the switch near the light switch. You might want at some point to leave the receptacle(s) hot and the lights off. In my barn I have receptacles all on separate circuits that I switched in order to turn them on and off from one point by the panel, rather than run around and plug/unplug or turn off/on the particular fan, heated bucket, lights, whatever. Overhead lights are all separate by zones of the barn with their own switches (it's an old 60 x 80 with a big hay loft).