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#62547 - 02/19/06 04:06 AM Multiwire Branch Circuits  
XtheEdgeX  Offline
Joined: Apr 2005
Posts: 116
Help straighten me out on this. While talking to someone in another forum, we seemed to disagree on MW branch circuits. He says that the ungrounded conductors in this circuit shall have a disconnecting means that will disconnect the circuits simultaniously at their panel of origin.
I say, that only applies to multiwire cicuits that attach to a device on the same yoke. Say a split duplex where each the top and bottom outlet is fed with a different circuit. Those types of installations require a multipole breaker to turn off both circuits. I also say, in a regular MW branch circuit setup, where each circuit takes care of it's own set of devices while each share a common neutral, that you do not have to have a single way to disconnect the circuits simultaniously. I think I'm right about this, but he cited Section 210.4
I even have a video,
Mike Holt

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#62548 - 02/19/06 06:19 AM Re: Multiwire Branch Circuits  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Usual caveat that I'm no NEC guru, but as I read 210.4(B) you are correct. It explicitly says that a common disconnect shall be provided when the circuit feeds devices or equipment on the same yolk.

210.4(C) would also require a common disconnect if the circuit feeds any 240V loads.

#62549 - 02/19/06 08:05 AM Re: Multiwire Branch Circuits  
winnie  Offline
Joined: Sep 2003
Posts: 649
boston, ma
XtheEdgeX: You are correct. A multi-wire branch circuit that serves entirely independent loads is not _required_ to be protected by multipole/tied breakers. You don't even have to put the breakers next to each other in the panel.

The 'common wisdom' on DIY boards is that while not required, tied breakers are a very good idea on multi-wire branch circuits. So if you are doing an installation somewhere where you suspect that non-_professionally_ qualified individuals will ever muck with the system, you should probably consider using a tied breaker as a design choice. (I don't want to start a 'DIY' good or bad discussion, simply suggesting that if one suspects a chance that DIY will happen in a particular situation, that one make slightly different design choices.)

I would also suggest that putting the breakers next to each other is a more 'professional' way to install a multi-wire branch circuit, and that somehow paring the hot conductors that share the neutral (say by tying them together near the breakers) is a good little note to leave for the next EC who opens the panel.


#62550 - 02/19/06 11:25 AM Re: Multiwire Branch Circuits  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,883
Brick, NJ USA
IF you're doing comm, office partitions (cubicles) read 605.6 & 605.7 ('05 NEC)



#62551 - 02/19/06 12:16 PM Re: Multiwire Branch Circuits  
XtheEdgeX  Offline
Joined: Apr 2005
Posts: 116
That's what I thought. I've installed MW branch circuits for many years, but when he cited, and I read section 210, it had me guessing. I didn't think all those engineered prints I've seen throughout my career were wrong. Thanks for the input.

#62552 - 02/19/06 01:28 PM Re: Multiwire Branch Circuits  
winnie  Offline
Joined: Sep 2003
Posts: 649
boston, ma
Hotline1, thanks. 210.4 giveth, 605.6 taketh away.


#62553 - 02/19/06 02:40 PM Re: Multiwire Branch Circuits  
Larry Fine  Offline
Joined: Feb 2005
Posts: 693
Richmond, VA
Edge, remember to never use device terminals for continuity of the neutral in multi-wire circuits. Use pigtails instead.

Larry Fine
Fine Electric Co.

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