Another elecrtical question

Here is a question maybe someone smarter than myself can answer. I assume the hot wire controls the breaker if it's overloaded. Is the common wire the same wire the same through out the panel. Can I take the common wire from one breaker and add it to another. Reason is I have a 110 circuit at my shed, and a separate 220 line. I need another 110 volt circuit. I want to use one leg on the 220 line and make another 110 line using the common from my 110 circuit already in my shed. Is this possible? Stan

In Idaho, under industrial code rules, two circuits can share a common neutral, two circuits under residential code rules cannot. That is all I know.

If I understand you want to use 2 breakers and connect common to one breaker. All the load centers I've seen all breakers are connected to a buss bar. There are two buss bars, both are connected to a 110v power leg. The two power legs together make 220v.

First I see no need to use a breaker on common leg. Second why make something that isn't needed. Third you would have to remove the power from one buss bar and connect that bar to common. Therefore only half the breakers in the panel will work. Again, WHY? You won't accomplish a single thing except make someone in the future ASK WHAT WAS HE DOING?

Actually this may create a dangerous situation. If common breaker trips power will still be going to load. Someone may think it's safe to work on. OUCH. Not a good idea.

Technically yes. Safely and legally NO. The common wire needs to belong to the same wire on the same breaker. What can happen is the next guy decides to move that wire in the main panel for some reason and turns off the 220 breaker. Then he unhook the neutral and grabs it only to get electrocuted because there was something plugged into the 110 outlet that you used this neutral on. In some places you can share a neutral but it needs to be in a cable assembly (romex,uf,etc) or in the case of conduit the neutral needs to be zip titled with the hot wires that it goes with.

Stan,

Best thing to do is put in a small sub panel in the shed, run the 220 into that, then out to 110 and 220 circuits.

I just want to use the same common for each breaker. Since the common eventually comes from the same place in the panel. I am trying to see if this will be a problem, some where down the line. Stan

37 Chief, If I understand your post, you're wanting to wire what's called in the trade a "Multi Wire Branch Circuit"

YES IT POSSIBLE IF DONE CORRECTLY but its NOT for amateurs who don't understand whats happening

A Multi Wire Branch Circuit has 4 wires: Two Hot Ungrounded Conductors (different legs of course),,,,,,,,, One Common Neutral GrounDED Conductor,,,,,,,,,,One Equipment GroundING Conductor. In my years as an Electrical Power Distribution Engineer I specified very few such circuits and indeed it saved money and time over having to run an extra Neutral wire. I would sever the duplex receptacles tie bar on the HOT side and wire one of the hot legs to each (top and bottom) but connect the single common Neutral over on the Neutral side. If both legs were feeding say an equal 16 or whatever equal amps NEUTRAL CURRENT WOULD BE ZERO. The advantage is there are twice as many available amps in the duplex receptacle if wired to a multi wire branch circuit. You could run one 1500 watt electric heater out the top duplex and another 1500 watts out the bottom, WITH ONLY A SINGLE NEUTRAL,,,,,,,, you CAN NOT do that on a standard wired duplex receptacle

HOWEVER realize there is 240 volts Line to Line inside that box versus only 120 volts in a standard branch circuit.
HOWEVER most lay Billy Bob and Bubba "home electrical experts" lol dont realize 240 is present
HOWEVER you must use a two pole tied circuit breaker such that you are turning off BOTH hots for working the receptacle.
HOWEVER if you have a lot of inductive loads like computer transformer power supplies where harmonic currents are present YOU
COULD OVERHEAT THE NEUTRAL. Best for resistive loads.

There's more but that's enough for now. As always Electrical and Legal questions draw the most responses.

Sorry if I misunderstood your post and question, but this is good info for lay persons regardless if they want to run a single common Neutral with two Hots.

John T Long retired and NEC has changed so NO WARRANTY

YES it can be a problem. However YES if done correctly using a two pole tied breaker so each hot leg is on a different phase IT CAN WORK...

Best to see my post above

John T

An issue with a duplex having a common white, and two hots at 220 is that (though unlikely), the devices could fail or get wet, when plugged in to that outlet, and have 220 between them. Not a favorite idea. Jim

If your common wire is big enough to carry the loads of both circuits at the same time. You don't want a common wire that is good for 20 amps then feed 20 amps from both circuits thru the one common.

I may be misunderstanding, however I took his post to mean something like this. I have a 12/2 uf feeding a 120 outlet in a shed and a 12/2uf feeding a 240v outlet in the same shed. Can I take the neutral from the first cable and use it with one leg of the second cable to have a second 120 circuit. Did I misread him?

Oops, it's getting late
I see what you are saying about the breaker, and it probably is technically legal. IMHO it is bad practice to use a neutral like that but there may be more to it that my foggy mind is not thinking of.

That would set up a loop that would befuddle an average guy looking at more wiring?

It would work as long as it works, but if something goes wrong its pretty easy for things to really go wrong because of the unexpected loop?

Paul

There are situations where it works out (but NOT if harmonic current are present) and it is NEC permissible. The breaker MUST be a two pole tied so BOTH circuits are turned off. Unfortunately amateurs and Billy Bobs out there have no idea whats going on while a professional qualified electrician does.

John T

Stan,
What kind of breaker are you going to use in a panel? All the load centers I've familiar with, one side of the breaker connects to the buss bar where you normally connect one power leg.

So, are you going to make one buss bar common and use a 220v breaker? Again WHY? The current in the power leg is equal to the current in the neutral leg, so why put a breaker in a leg that can't short to ground because it's connected to ground?

I really don't understand what you are trying to accomplish.

Load centers are normally wired with a larger guage wire for L1 and L2 and a smaller wire for common, because if have equal loads, currents are the same on both legs, there is no current on common leg. Why not run 220v to load center?
George

(quoted from post at 22:16:58 09/01/15) If your common wire is big enough to carry the loads of both circuits at the same time. You don't want a common wire that is good for 20 amps then feed 20 amps from both circuits thru the one common.

Click to expand...

No. If the two live lines are supplied from line 1 and line 2 . Then a common neutral is perfectly legal . In fact if the loads on line 1 and line 2 are identical . Current flow on the common neutral will be zero.
Only however if the three insulated load carrying wires and the ground are in the same cable or conduit .