OK, so my cottage had a flood this spring and I will need to replace some NMD wire that got fully submerged for a while. The NMD wire was inside the crawlspace to a junction box where it connected to some outside wire going to two sheds.

The person who wired it up used 3 way wire. In the breaker box I had the white going to the neutral bar, the ground going to the ground bar and the red to one 15 amp breaker and the black to another 15 breaker, just below it.

My question is this. I understand that both the black and the red are hot wires, each capable of carrying 15A, allowing for two separate circuits. Now if I was to run 15A on both circuits at the same time, would the white not be now carrying 30 A, when 3 way wire is used, well above its capacity rating?

Lastly, the breakers in the box were simply two seperate 15A breakers. Is there a device that I can put on these so that a person is forced to turn both off for servicing as opposed to just one. I suspect they should already be like that but they are not. I don't want to have to buy a separate breaker.

Thanks for your help.

 

You have what is called a multi wire branch circuit. It is very important that the two hot wire be on separate legs of the service. There should 240 volts between. The neutral will only carry the difference between the hots not the sum since the current on one hot (for lack of better term) cancels the equivalent current on the other hot. If both hots are on the same leg of the panel then the currents will add up.

This a perfect acceptable setup.

 

Yes, it's called a handle tie. Every manufacturer makes them for their particular brand of breaker.

 

Thanks guys. That helps.

 

Normally a double pole breaker is used. However a interlock device as provided by the manufacturer can be used. You can't just stick a nail through the holes in the handle.

 

Why not ? It was perfectly acceptable when I started forty years ago.

 

Why not?
Because code in Canada says.
14-302

 

joed...... I'm just joking with you.

 

I saw the grin face after I posted but figure it is a good reference for anyone reading this.

 

I suppose you could still use this method if you use a UL Listed nail.