2 circuits sharing a neutral

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bbartmasse r

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Hello,

Doing some residential re-wiring in a panel and came across something which I assume is common but I have not seen before(I am not too experienced).

The fridge circuit and Microwave circuit are served by one, 12-3 wire, sharing the neutral. I think there is another couple circuits like this, but I cannot remember what they serve.

They originally were not on double pull or handle tied breakers, do they need to be? Is this what is called a MWBC? They appear to be legal. Are they accepted as good practice these days?

thanks

Brett
 
Their are still millions upon millions of circuit breakers that share a neutral.

It's been a common practice for many years and still is in many jurisdictions across the nation. How ever the NEC has now required the circuits sharing a neutral. They must all be able to be turned off with one breaker.
Take a look at 240.15

If you're working on a circuit that is off and get between a neutral that is still being utilized. You can and will be zapped:happysad:
 
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Hi Brett,

It's time to go back to first year apprentice theory, and reread it. This is important stuff, as the Multiwire Branch Circuit is a microcosm of a repeating pattern that is throughout the generic single family 240 / 120 Volt three wire single phase Premises Wiring (System).

(If some of those terms are not clear to you, also going to the Article 100 Definition and revisiting them is in order.)

In my opinion, your question is a great one, because the returning to the basics, in my opinion, is a lifelong part of the learning that never stops in our profession.
 
bbartmasse r said:
Hello,


They originally were not on double pull or handle tied breakers, do they need to be? Is this what is called a MWBC? They appear to be legal. Are they accepted as good practice these days?

thanks

Brett
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Depends on what code cycle the house was built under. Before some decided it was necessary to dumb down the code, MWBC's did not have too be handle tied. They were legal, good practice, and efficient in a number of ways.


Roger
 
When I started in the trade, the only MWBC's that needed handle ties were if both "circuits" landed on the same device - split receptacles being most common place it applied.

I seem to recall at some point it was changed to still include same device for any application, but also required any MWBC in a dwelling to have handle ties or common trip breakers. Then eventually got changed to what we have now - which is basically all MWBC's need handle ties or common trip breakers.
 
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