Breaker placement is important when sharing a neutral. Keep your 👀 open! #electrician #electrical

[rarelampcollector]

For all the non electricians that are trying to wrap their heads around what's going on with this shared neutral problem, this is what's known as a multiwire branch circuit, using a 12/3 NM cable to feed two 120 volt circuits, using a common neutral. When done properly, you would measure approximately 240 volts between the black and red, and approximately 120 volts between the black or red to the neutral, which carries the difference between the current in the black and red, ex 13 amps on black, 10 amps on red, the neutral carries 3 amps.

In this problem panel the black and red are connected to the same bus bar, so you'd read 0 volts between black and red, and 120 volts between either black or red to neutral, and in the example above with the 13 & 10 amps on black and red respectively, the neutral carries the sum of currents, in this case 23 amps. Also, a 240 volt appliance wouldn't work properly or at all. Examples, a clothes dryer would probably still operate the motors and electronic controls but won't heat. An electric water heater won't work at all.

[dontnewyorkmyflorida]

This is why in new construction you're not going to use any three-wire except for 3-way switches and smoke detector interconnect because everything now has to be on arc faults or dual functions and it's a single feed with a single neutral wire now, and the situation he's in right now those should all be double pole breakers to disconnect both legs at the same time

[davidhargrove]

Old school here and this mistake is so common yet so important to correct. Also people don’t always know that simultaneously disconnecting all energized conductors on a multi wire circuit was not required several years back unless they were landed on the same device yoke. Today multi wire circuits with shared neutrals are obsolete in residential wiring because of the implementation of arc fault and ground fault breakers. Although I stopped using MW circuits in residential years ago except in kitchens, but eventually no where.

[Lakeman]

The National Electrical Code (NEC) has requirements for shared neutral conductors, also known as multiwire branch circuits (MWBCs) or common neutral circuits:
200.4(B): When more than one neutral conductor is associated with different circuits in an enclosure, the grounded circuit conductors of each circuit must be identified or grouped. This can be done with wire markers, cable ties, or similar means in at least one location within the enclosure.
200.4: Neutral conductors should not be shared unless specifically permitted to be shared elsewhere in the code. This is because overloaded neutral conductors can be a problem due to harmonic currents generated by switching power supplies. Dedicated neutral conductors can help eliminate this problem.
310.6(A): Insulated neutral conductors must be identified as white or gray.

[GailUrge-vqqn]

My legs need a break from doubling the load . . . I'm gonna put it in neutral.

[zacharydavid]

The proper term would be putting them on opposite phases.

[marcemarc]

A lot of electricians I know rarely run branch circuits. The savings on wire is so minimal. I can tell you how many times I’ve traced out wires to see them on the same leg, untied breakers or different legs

[jonkilowatt]

This is why I never use those slims( tiny breakers). Add a sub panel if you need more circuits.

[andrewjones]

It's called an unbalanced load it needs to be A and B phase also the breakers should be joined together in case one trips the other one will to

[levinetate]

At first I was confused until I listened carefully and you said 12/3, it made more sense about the shared neutral

[garymiller]

Also you forgot to mention that Common trip breaker, somebody can get killed on that neutral You don't simultaneously shut off both

[joelboutier]

Ya thanks for reminding us. It's easy to overlook with the 1/2" breakers

[Aloha_XERO]

finally a video showing exactly my current issue (no pun intended)

[paulyp]

Multi-wire circuits are not allowed anymore in the state of massachusetts. Even if, and when it was allowed must be a two pole breaker!

[Calicostring]

Yes, a 2-pole breaker is required. This is a "multi-wire branch circuit".🎉 However, you neglected to mention: That required 2-pole breaker MUST be a "common-trip" breaker (the handles tied/connected together). This ensures that BOTH phases are disconnected in the event of an overload on either one.

[jamescody]

It won't force you to put it on two separate legs, but a two pull breaker will turn off both circuits ensuring that neutral is also dead. You could also just bridge the two handles with a breaker handle bridge

[kevinberniebarron]

Great video! Thank you for sharing your knowledge and expertise!
God bless you and your family

[CM-klqh]

I discovered this form of writing (shared neutral lighting) in my new 25+ year old house. I’d never seen it before. I don’t know if it’s in code for new construction but if I were building new it would be in the contract all 120v circuits would be 12/2 w/G and an independent breaker! By using 12/3 they’re trying to avoid using two “extra” wires and creating potentially hazardous conditions! It would be in the contract!

[io]

And they're supposed to be interconnected

they share the neutral which means if one legs trips the other one has to be disconnected simultaneously.

[MrApluscircuit]

The double breaker also serves as a protection.. that wire will go into one box and when you shut off a double pole breaker, both legs will be dead..