1

We recently bought a 1978 home in Florida.

The kitchen wiring leaves me scratching my head. I think I have solved 2 of 3 major problems, but need advice on the last.

(see pic)Circuit diagram

4 different 20A tandem breakers in play. One of them was split into 2 INSIDE the breaker panel, one was split in a gang box so I am dealing with 6 "hot" wires & only 4 neutral wires.

1) 12/3 Romex. Black/neutral on one breaker [16 L] leads to kitchen GFCI outlet --> regular outlet --> kitchen light switch --> kitchen light. Red "hot" [14 L] leads to light (former fan) in living room with light fixture neutral connected to neutral wire from the kitchen breaker.

To solve the shared neutral problem, we disconnected the living light and connected it inline with the living room outlets using 12/2.

(The kitchen light is downline from a GFCI which isn't ideal but I don't want to mess with what works.)

2) Breaker 16 L splits inside the breaker box with a hot single black wire through conduit to the other side of the kitchen. That wire powered the microwave, dishwasher + 2 outlets and had NO neutral. (Neutral for this breaker is on other side of room in the 12/3.)

In that SAME conduit are a hot/neutral from breaker 14 R. This was used to power the garbage disposal through an under-sink outlet. The neutral from 14 R was then wired up from the disposal outlet & connected to ALL of the other appliances/outlets on 16 L.

To solve this shared neutral, we 1st removed the microwave and put it on it's own 20A circuit.

Next thing was to disconnect everything & wire the 14 R breaker from dishwasher outlet ---> disposal switch ---> GFCI under-sink outlet.

3) That leaves us with 2 outlets adjacent to the sink with power but no neutral.

QUESTION:

Would it be better to splice in a neutral wire from one side of the kitchen to the other. There is a junction box directly above, so it should be fairly easy.

OR

Would it be better to remove the splice on 16L inside the breaker box and run a whole new 12/2 to the sink outlets?

My concern splicing a neutral is with using GFCI outlets and having the same neutral run through GFCI outlets on both sides of the room. Would that cause problems?

My concern with running new wire is using up 4 breakers just for the kitchen.

Thanks for any advice!

  • Also, can I presume there is a cable between the kitchen light and the living room light, and not just a solo wire? – ThreePhaseEel Oct 7 '17 at 22:36
  • Is there a way you can replace that 12/2 you ran to fix the living room light with a 12/3? – ThreePhaseEel Oct 7 '17 at 23:39
1

Ok. The fundamental rule is that currents must be equal in every cable or conduit.

Yes, current travels in a loop. But in actual practice, we squeeze that into a "tree" topology. Imagine you draw a tree on a piece of paper, and send an army of 2-dimensional ants (current) to explore the tree. They are not allowed to hop across branches, but they can wander from branch to branch without going back to the bottom of the trunk. At any point on the tree, if you count the total ant passages, exactly the same number of ants (current) go up any branch as come back down.

This equal flow assures the current does not induce magnetic fields and eddy-current heating into nails, sinks, piping and other metal parts of your house.

Now it's OK to have 3 wires, 10A going out on one, 2A going out on the other, and 12A returning on the third. That's still equal. That's how a sometimes-on switch wire can travel with an always-hot.

Multi-wire branch circuits

That is also how a multi-wire branch circuit works, which is what you have on 14L and 16L. It's not an accident they are 2 numbers apart; they must be on opposite poles or they will overload the neutral.

And it's perfectly fine for part of a multi-wire branch circuit to have one side branch off in another direction, as in 16L. However its neutral must run with the partner hot. So whatever is going on in 16L, you must make sure that wherever the hot runs, the neutral is right next to it.

If you're working in conduit, as I suspect you are, your local actual electrical supply house sells THHN wire in 11 colors and tape in 10. Use different colors. Gray and white are both legal for neutrals, so when you have two circuits in close proximity, ask them to sell you some gray neutral wire.

You see where there are points where the MWBC splits off to just one hot with just one neutral. That is a prerequisite for working with GFCI+receptacle devices. That is fine, again, keep the hot with the neutral at all times. Now, a few new Code requirements with MWBC:

Anywhere both sides rely on the same neutral, the neutral must be pigtailed. You must be able to remove the device without interrupting the neutral wire for either side.

Both sides of the MWBC must have a common maintenance shutoff, which in practice means thet must be on a 2-pole breaker. When dealing with duplex, you get a "quadplex" that is a 2-pole in the middle and two singles on the outside, like this one.

  • "Anywhere both sides rely on the same neutral, the neutral must be pigtailed. You must be able to remove the device without interrupting the neutral wire for either side." Thank you. I was wondering why it was set up like that. I didn't consider potential removal of the device. – FL1sthome Oct 8 '17 at 1:52
  • Thank you so much for the excellent explanation. I was just confused as to using a MWBC on tandem breakers. I thought the 2 breakers with the shared neutral needed to be coupled together so they would trip at the same time. Ours are not, so I was concerned about the possible return load on the neutral if one trips and the other doesn't. – FL1sthome Oct 8 '17 at 2:01
  • @FL1sthome -- a one-sided trip is OK because in that case, the neutral current can't be higher than what the other side can provide. You just need to have both sides shut off at once when you disconnect the circuit for maintenance. – ThreePhaseEel Oct 8 '17 at 2:15
1

Pull a new homerun

You'll want to take some 12/2 and pull a new homerun (you could unhook the red wire from 14L with that breaker off, cap it off in the panel, and land the new homerun on 14L, even) for the currently unpowered outlets in the kitchen. This simplifies things considerably down the road, and also fixes a NEC 210.11(C)(1) violation that's likely been there for the life of the house:

(C) Dwelling Units.

(1) Small Appliance Branch Circuits. In addition to the number of branch circuits required by other parts of this section, two or more 20-ampere small-appliance branch circuits shall be provided for all receptacle outlets specified by 210.52(B).

Move the kitchen light to the right circuit

Right now, the kitchen light violates NEC 210.52(B)(2):

(2) No Other Outlets. The two or more small-appliance branch circuits specified in 210.52(B)(1) shall have no other outlets.

Exception No. 1: A receptacle installed solely for the electrical supply to and support of an electric clock in any of the rooms specified in 210.52(B)(1).

Exception No.2: Receptacles installed to provide power for supplemental equipment and lighting on gas-fired ranges, ovens, or counter-mounted cooking units.

Moving the kitchen light to the living room circuit would work, save for not having an always-hot at the living room light fixture's box -- replacing the 12/2 you ran with 12/3 and connecting the black and white as before, but pigtailing the red to the power feed to the switch in the living room switch box will let you fix that.

Once that's done, you can convert the 12/3 between the kitchen switch and the kitchen light into a new-style switch loop powered from the cable between the kitchen light and the living room light. To do this, you can (with the power on 14L, 16L, and 15 off of course!):

  1. Unhook the two red wires in the kitchen switch box. Cap off the one from the incoming kitchen receptacle feed.
  2. Unhook the pigtail from the kitchen switch that connects to the black wires in the kitchen switch box. Connect it to the red wire going out to the kitchen light.
  3. Unhook the neutral (white wire) out to the kitchen light from the other neutrals in the kitchen switch box and cap it off.
  4. Connect the neutrals (white wires) in the kitchen light box together. Don't forget to connect neutral to the kitchen light!
  5. Connect the red wires in the kitchen light box together. This will provide power to the kitchen light switch when we're done.
  6. Connect the neutrals (white wires) in the living room light box together. Don't forget to connect neutral to the living room light!
  7. Connect the red wires in the living room light box together. This means that the kitchen light is now completely powered from the living room circuit (15).
  8. Button it all up, turn the circuits back on, and enjoy!
  • Thank you! The 12/2 for the living room light was actually already in the gang box (cut off & disconnected of course). It would be very easy to change to 12/3 as you suggest. And yes, there was cable between the 2 lights. I should have indicated that! – FL1sthome Oct 8 '17 at 1:50
  • We're going to tackle this in the a.m. and keep you posted. Thank you for taking the time to write such a detailed explanation. I feel much more comfortable now. – FL1sthome Oct 8 '17 at 2:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.