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Old 09-13-2012, 12:44 PM   #16
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DW and GD MWBC


If you are going to go with the MWBC, be aware that the two circuits need to be on "opposing legs" of the panel and a "tie-bar" breaker is required - like a double breaker for a 240 volt circuit.

The tie bar assures *both* circuits are turned off for maintenance. If just one circuit is turned off and the neutral is "messed with" on such a circuit, you could be shocked by touching the neutral!

And the "magic" of an MWBC is by using opposing legs. If both circuits are on the same leg, then the shared neutral can overload and cause a fire.

Be sure to totally understand how this circuit works.
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Old 09-13-2012, 12:48 PM   #17
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DW and GD MWBC


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Originally Posted by Billy_Bob View Post
If you are going to go with the MWBC, be aware that the two circuits need to be on "opposing legs" of the panel and a "tie-bar" breaker is required - like a double breaker for a 240 volt circuit.

The tie bar assures *both* circuits are turned off for maintenance. If just one circuit is turned off and the neutral is "messed with" on such a circuit, you could be shocked by touching the neutral!

And the "magic" of an MWBC is by using opposing legs. If both circuits are on the same leg, then the shared neutral can overload and cause a fire.

Be sure to totally understand how this circuit works.
Thanks Billy Bob. Yeah, I am aware of all that. Just to be 100% sure though, in the last picture hammerlane put up, which wire would connect to which breaker, or does it matter if I am using a double breaker. Would two single breakers be better with a tie-bar?
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Old 09-13-2012, 01:01 PM   #18
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DW and GD MWBC


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which wire would connect to which breaker
doesnt matter as long as they are attached to breakers on opposing legs
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Old 09-13-2012, 01:21 PM   #19
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DW and GD MWBC


The grounded conductor at the switch, isn't required until the 2011 NEC.
Even then (now) if the box can be accessed easily to add one later, its still not required.
I think disposal switch would fall under that exception
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Old 09-13-2012, 01:32 PM   #20
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DW and GD MWBC


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WHy would you use 12-2 for the switch loop?
There is no purpose to add a third conductor ( either by code or logic).
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