Shared Neutral?

AdamBNYC

Hello Pro's

I ripped down the basement sheetrock ceiling in my 1926 house to take a good look at the wiring and also so I can continue with my generator connection project.

I'm seeing something that I am not completely comfortable with and I wanted to get some feedback on if this is OK or not.

My house still has some knob tube hanging around. I've undertaken the project of removing all this old stuff. I can see that my house is a museum of electrical cabling over the century. I have some K/T, I have some, old AC, some newer AC, some older romex, and some newer romex, Heck, I even discovered some gas lighting

So first off, i found buried junction boxes. I know this is a no go. But my main concern here is that a single 14/3 is run into this box. This 14/3 goes to the circuit breaker panel. They took the red hot wire and put that into one 20 amp breaker, then they took the black hot and put that into a different 20 amp breaker. back in the junction box, they shared the neutral between 2 totally different circuits that splice into K/T in the junction box.

This just doesn't seem right to me. Am i wrong in thinking that this is just plain wrong and they are actually sending 40 amps back over the neutral at full load? Also, i dont think K/T is 12 gauge wire, probably more like 14. Wouldn't i want to give each their own 14/2 on separate 15 amp breakers?

Thanks for the input.

darren

Common worry among DIY but as long as it is done right what you have is perfectly fine, minus the junction onto the k and t.

When you do this it is called a multi wire branch circuit and you have to make sure your two hots end up on different phases in your panel, this is usually done by putting the two hots together(one on the top of the other). As long as the hots are on different phases the current on the neutral will cancel each other(phase A has 12A and phase B has 14A) so you would have 2A on the neutral. If both hots were on the same phase the neutral current would be additive so in our example you would have 26A.

The easiest way to check to make there they are on two different phases is to measure the voltage at the terminal screws on the breaker. If you measure 240V then they are on seperate phases if it measures 0V then there on the same phase.

jbfan

The breakers need to be changed to 15 amp also.
Are you going to remove the K&T now that the drywall is down?

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AdamBNYC

Thanks Darren,

You guys on here are the best. I usually post a question and within 10 minutes its answered. I greatly appreciate it! And you are 100% correct. The two breakers are stacked directly on top of each other so they are on different phases.

Great info to know as this will help me going forward with the upgrade now that I understand how to safely do this and check to make sure that I did it properly.

AdamBNYC

The plan is to get rid of all K&T. going to be challenging at some spots. the house is plaster and lathe also, so that doesnt make things any easier. On a side note, is it ok to abandon K&T in place? Getting the wire off the knob can be a real PIA without breaking down the wall.

Edit - The plan is to upgrade all wiring throughout the entire house with new 12 romex. I'm going to use 12 romex even for 15 amp breakers just in case.

darren

Not necessarily, in the majority of panels this is correct. We have one type of panel in Canada where you can put two breakers stacked on top of each other and they will be on the same phase.

Let us know what type of panel you have and we will be able to tell you if you have to worry about something like that.

AdamBNYC

I have a newer seimens panel. was installed 2 years ago.

k_buz

Just to add a little information...

It is legal to refeed knob and tube wiring, but it is not legal to extend it.

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fa_f3_20

Yeah, this is what's called a "multi-wire branch circuit". The only thing wrong with yours is the 20A breakers; should be a maximum of 15A for 14 gauge. If you're going to replace them, get a single two-pole breaker instead of two separate breakers.