Multiwire circuits

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HKC

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On a 4 wire, 208/120 3 phase system, are multiple home runs in a common conduit considered a multiwire branch circuit that will require a simultaneous disconnect means, i.e. run phase A, B, C and a neutral in a conduit to a junction box? It appears to meet the definition but most of the time I have not seen the 3 phase breaker used. :-?
 
Yes, A,B, and C, phases sharing a neutral is a MWBC and until the 2008 cycle, only circuits landing on a common yoke required the breakers to be handle tied or a multipole breaker used.

In the 2008 NEC all MWBC's are required to have the OCPD's tied together or use a multi-pole breaker.

See 210.4

Roger
 
Multiwire circuits

Roger, thanks for the confirmation. After your response I did compare the 2008 to the older codes and see the change. It seems this will require a lot more coordination with breakers when using MWBC to save conduit for home runs.
 
You're welcome and your future posts should appear faster.

Roger
 
multiwire cicuits

multiwire cicuits

Does it mean that, with this rule each of the receptacle circuits need to have dedicated neutral or else we would to have 3 pole circuit breaker?


Now, if we did that then for three consecutive cirucuits we will have 3ph+3N+1G wire and wiring has to be derated as per nec.
 
pdesai_pe said:
Now, if we did that then for three consecutive cirucuits we will have 3ph+3N+1G wire and wiring has to be derated as per nec.
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Yup, so in some instances a 50 cent handle tie may be a lot more cost effective. :rolleyes:
 
pdesai_pe said:
Does it mean that, with this rule each of the receptacle circuits need to have dedicated neutral or else we would to have 3 pole circuit breaker?


Now, if we did that then for three consecutive cirucuits we will have 3ph+3N+1G wire and wiring has to be derated as per nec.
Click to expand...

Yep and its probably cheaper to buy a 3 pole breaker. I am not sure they make breaker ties for 3 sp breakers
 
alfiesauce said:
This also would apply for 3-wire romex as well?
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It applies to all MWBC - regardless of the wiring method.

2008 NEC said:
210.4(B) Disconnecting Means.
Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.
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The '05 differed slightly:
2005 NEC said:
210.4(B) Devices or Equipment.
Where a multiwire branch circuit supplies more than one device or equipment on the same yoke, a means shall be provided to disconnect simultaneously all ungrounded conductors supplying those devices or equipment at the point where the branch circuit originates
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This will affect a 12/3 for the SABC, et al, in resi. applications.
 
celtic said:
It applies to all MWBC - regardless of the wiring method.


The '05 differed slightly:


This will affect a 12/3 for the SABC, et al, in resi. applications.
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Sure go and get right to the point. How are we to drag the post out for weeks on end if you just go and blurt out the answer???????:grin:
 
acrwc10 said:
Sure go and get right to the point. How are we to drag the post out for weeks on end if you just go and blurt out the answer???????:grin:
Click to expand...

Don't you worry...if the the thread gets stagnant I can find a way to stir the pot up :grin:
 
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