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Old 01-07-2015, 07:05 AM   #16
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Lost neutrals on MWBCs can cause 240V to be applied to 120V equipment. The pigtail reduces the chances of problems.
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Old 01-07-2015, 09:13 AM   #17
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Because the NEC requires it.

Mark

Thanks. Good reason.

I'll have to check my Ontario code for this.
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Old 01-07-2015, 09:17 AM   #18
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Lost neutrals on MWBCs can cause 240V to be applied to 120V equipment. The pigtail reduces the chances of problems.
Thanks.
Lost neutral? So if contact from the hot side gets to the neutral, it'll send 240 volts down the line? And we know this because the two breakers for the MWBC are on different legs, correct?
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Old 01-07-2015, 09:43 AM   #19
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You want the power to flow hot-to-neutral. If this is happening you get 120V. If you lose the neutral, power can flow hot-to-hot, which it 240V because the two hots are on different legs.
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Old 01-07-2015, 10:17 AM   #20
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Thanks.

1/2" breakers, one on top of the other in the panel.
These would be on the same leg, correct? Or is this not what you're referring to?
Did you ever find out if you have a mwbc at the outlet?
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Old 01-07-2015, 10:25 AM   #21
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Quote:
Originally Posted by busman View Post
Because the NEC requires it.

Mark
NEC only requires it on MWBC. It is not requires on normal circuits.
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Old 01-07-2015, 11:55 AM   #22
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Did you ever find out if you have a mwbc at the outlet?
There was a blue wire running thru the conduit directly to the light switch downstream. If that what a MWBC is. Maybe I'm thinking the wrong thing.

I'm not a total electrical newb. I build restaurant equipment and we use 3 phase panels for load centers and run all the wiring.
Just never ran two hots and a neutral together before. I'll have to ask our inspector about this next time he comes by.
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Old 01-07-2015, 12:19 PM   #23
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There was a blue wire running thru the conduit directly to the light switch downstream. If that what a MWBC is. Maybe I'm thinking the wrong thing.

I'm not a total electrical newb. I build restaurant equipment and we use 3 phase panels for load centers and run all the wiring.
Just never ran two hots and a neutral together before. I'll have to ask our inspector about this next time he comes by.
Measure the voltage between the two hot slots of the outlet. Based on my reading comprehension and what I believe is going on, if you read zero, they are on the same phase and not a mwbc. If this is the case, I would keep the neutrals separate and treat this as two circuits. If you read 120 volts you may or may not have a mwbc and will need to investigate further.

I have an outlet at my shop, which is fed from two separate circuits (top and bottom) and is not part of a mwbc for what ever reason.

Added, just reread your post, how many wires are in this box? Mine has two hots and two neutrals.

Last edited by 47_47; 01-07-2015 at 12:23 PM. Reason: Added
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Old 01-07-2015, 02:25 PM   #24
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Quote:
Originally Posted by 47_47 View Post
Measure the voltage between the two hot slots of the outlet. Based on my reading comprehension and what I believe is going on, if you read zero, they are on the same phase and not a mwbc. If this is the case, I would keep the neutrals separate and treat this as two circuits. If you read 120 volts you may or may not have a mwbc and will need to investigate further.

I have an outlet at my shop, which is fed from two separate circuits (top and bottom) and is not part of a mwbc for what ever reason.

Added, just reread your post, how many wires are in this box? Mine has two hots and two neutrals.
This circuit has two hots from two breakers and a shared neutral.
A separate blue wire bypasses the receptacles to feed the lighting circuit.
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