# Thread: 12/3 wire, two separate circuits

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1. Junior Member
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Apr 2012
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## 12/3 wire, two separate circuits

I live in an old house, with 2 apartments, that still has fuses. The electrical wire that supplies the kitchen is 12/3. One 20 amp circuit supplies the fridge, the other 15 amp circuit supplies the outlet on the counter and the light over the sink.

I've read this type of setup is acceptable if the two circuits are on separate poles (or leads). If the two circuits are on the same pole, the neutral wire can be overloaded. But all of what I've read refers to circuit breakers, not fuses.

My fuse box has 6 round fuses; 3 on the right side, 3 on the left. The circuits in question are both on the left hand side, one above the other.

I've read that to tell if the circuits are on separate poles is to test the voltage between the 2 circuits. If you get a 240 volt reading, the circuits are on separate poles and are safe from overloading the neutral. But if you get 0 volts, the 2 circuits are on the same pole and are not safe.

I tested the voltage and it is ZERO between the two circuits. If I test a circuit on the left with a circuit on the right, I get the 240 volt reading.

From my understanding I need to switch the wires so one is on the left side and one is on the right side; which will be fairly easy to do.

But I want to be sure this is what I'm supposed to do before I go ahead.

From my understanding this house was split into 2 apartments sometime in the 60's, so this electrical setup with the 12/3 wire has been in place since that time, with no know problems. (house still standing!!)

Any advice would be a big help.

Thanks,

2. Member Rank 1
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wisconsin
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## Re: 12/3 wire, two separate circuits

Id have to say you are correct in all you said.

3. ## Re: 12/3 wire, two separate circuits

I agree with sparky1, however I would like to ask if the wiring is 12ga. or 14ga.? If it is 12 I would make both 20 amp circuits, if it is 14 make both 15 amp circuits.

Jack

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Apr 2012
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## Re: 12/3 wire, two separate circuits

All wiring is 12 gauge, including the sink light.

Why make both circuits the same amps? Is this to make things even? If both circuits maxed out at 20 amps each, neutral wire would be zero amps, correct? Is even 5 amps through neutral bad?

5. ## Re: 12/3 wire, two separate circuits

It is always best the balance circuits. If one line maxes at 20 amps and the other has no load there would be 20 amps on the neutral, if both circuits have the same load there is zero amps on the neutral.

Jack

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## Re: 12/3 wire, two separate circuits

Ok, sounds good.

Also, I just want to be sure. I don't need to make any changes to the neutral wire? I just simply (hopefully) need to switch one of the wires on one of the circuits on the right hand side of the fuse box with one of the wires from the 12/3 circuit in question that is on the left side of the box?

7. ## Re: 12/3 wire, two separate circuits

Originally Posted by BillyB1976
All wiring is 12 gauge, including the sink light.

Why make both circuits the same amps? Is this to make things even? If both circuits maxed out at 20 amps each, neutral wire would be zero amps, correct? Is even 5 amps through neutral bad?
Ideally with a shared neutral it's best to have both circuits balanced so the net current on the neutral is zero --- realistically as low as possible.
However with having 20 amps on one leg and 15 amps on the other things are already unbalanced form the get go.

The other thing that comes to mind is the need to have the correct double pole fuse block. This will ensure that each circuit is on an opposite buss leg -- but -- more importantly for saftey the double pole fuse block should be "pullouts" .

In event you need to work on one circuit ( say changing out the counter receptacle or light ) you need to ensure the other circuit is also disabled since current would still be on the neutral otherwise --- creating a shock hazard.

Those "pullouts" are designed to have hinged interlocking covers on them on them that prevent the fuses being unscrewed without removing the whole "pullout", so both sides of the circuit are dead.

As Jack mentioned either have them both 15 or 20 amp and if the counter plug isn't GFCI it would be a good idea to change it to include one.

8. Junior Member
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Apr 2012
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## Re: 12/3 wire, two separate circuits

A fuse pullout is not an option. Besides the main pullout, the only other pullout in the box is for the oven. There are no empty spaces to add one. I guess the best I could do is write a note in the box explaining that both fuses need to be removed to work on those two circuits. The whole box should be replaced with breakers, but that is not an option at this time.

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