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Thread: MWBC Question Again

  1. #21
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    A change in language in 210.4(B) came about in 2008 where the requirement for a simultaneous disconnect went from just being on the same yoke to any MWBC. So, going forward it was a good rule change but looking back, we have to ask what happens now to all those MWBC's that weren't connected to 2-pole breakers ? They still exist and still pose shock hazards.

    In the State of NJ we are not required to make the change to 2-pole breakers on MWBC's when performing a service upgrade but are required to do so on new construction. I'm not sure why that is, given the fact that an MWBC poses such a shock hazard. My only guess is that s/p breakers for MWBC's were Code compliant at the time of initial installation.

    Having said all of that I want to thank all of you who responded. I fully understood all the explanations and reasoning presented as to why a 2-pole breaker should be used for an MWBC. However, I still think there needs to be an exception to the rule for certain scenarios like the ones I presented. If you disagree - so be it. When required I will make this installation in compliance with the Code but I will still disagree with the reasoning (in my specific case).

  2. #22
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    Quote Originally Posted by goldstar View Post
    we are not required to make the change to 2-pole breakers on MWBC's when performing a service upgrade but are required to do so on new construction. I'm not sure why that is, given the fact that an MWBC poses such a shock hazard.
    The main reason is because just like any change, you've got to start somewhere.

    JAP>

  3. #23
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    Quote Originally Posted by goldstar View Post
    So, if I run two separate 120V circuits into a 2-gang JB and land the circuit wires on two separate receptacles, can I then use s/p breakers ? Or, am I required to disconnect all power to the JB ?
    Shhh, don't give CMP's any more ideas, or we will be seeing 9 pole handle ties (or more) in the future.


    Quote Originally Posted by goldstar View Post
    I understand that and I can buy into the logic behind the Code section. However, from the standpoint of safety, I don't see the logic if you have 2 separate circuits when you have separate neutrals. If you run an MWBC into a 2-gang box and are installing 2 duplex receptacles, you're splicing the neutrals under a wire nut and terminating the tails onto each receptacle. What's the difference, from the standpoint of safety ?
    If you have two "hot" and two neutrals but land on the same yoke - they want to assure you turned off both supply circuits to a single item. IIRC that was the rule before they decided we need handle ties on all MWBC's. Yes, at one time it was acceptable to not have handle ties, maybe around 1999 or 2002 when this changed, 2005 at the latest I think.
    I live for today, I'm just a day behind.

  4. #24
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    210(4)(B) was the ultimate example of dummbing down of the code. There is nothing unsafe about about a MWBC to anybody who is qualified to work on one. There are millions of not handle tied MWBCs in use right now operating safely. From Edison till 2008 we had MWBCs without handle ties. Worst code change ever.
    If you go and decide to dance with a gorilla the dance ain't over till the gorilla decides it's over.

  5. #25
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    Quote Originally Posted by ActionDave View Post
    210(4)(B) was the ultimate example of dummbing down of the code. There is nothing unsafe about about a MWBC to anybody who is qualified to work on one. There are millions of not handle tied MWBCs in use right now operating safely. From Edison till 2008 we had MWBCs without handle ties. Worst code change ever.
    I agree but there have been accidents where skilled electricians have been injured or killed. For me the requirement should not be for less than 150 volts to ground circuits. 480/277 is a different story.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  6. #26
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    Quote Originally Posted by infinity View Post
    I agree but there have been accidents where skilled electricians have been injured or killed. For me the requirement should not be for less than 150 volts to ground circuits. 480/277 is a different story.
    I think being forced to shut off three circuits instead of one makes it more likely someone will choose to work hot.

    I also think MWBC will die off in my lifetime. They will either be made illegal or they will be not allowed by job specs.

  7. #27
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    Quote Originally Posted by ActionDave View Post
    I think being forced to shut off three circuits instead of one makes it more likely someone will choose to work hot.

    I also think MWBC will die off in my lifetime. They will either be made illegal or they will be not allowed by job specs.
    I see very few MWBC now. Installation headaches along with the problems associated with having tow or three breakers open due to one "fault" make them less desirable.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  8. #28
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    Quote Originally Posted by augie47 View Post
    I see very few MWBC now. Installation headaches along with the problems associated with having tow or three breakers open due to one "fault" make them less desirable.
    And AFCI requirements have pretty much eliminated them in dwellings and a few other places. Not that they are prohibited, just impractical.
    I live for today, I'm just a day behind.

  9. #29
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    Quote Originally Posted by augie47 View Post
    I see very few MWBC now. Installation headaches along with the problems associated with having tow or three breakers open due to one "fault" make them less desirable.
    Some handle ties are constructed so that a fault in one breaker will not turn of the other breaker(s).

  10. #30
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    Quote Originally Posted by ActionDave View Post
    210(4)(B) was the ultimate example of dummbing down of the code. There is nothing unsafe about about a MWBC to anybody who is qualified to work on one.
    Now there you have it !!! That was the whole point I was trying to make. Who else but someone like one of us is going to work on a MWBC knowing it's live? As soon as you pull the cover plate off the quad receptacle and look inside you'll know it's a MWBC. If you don't - then you shouldn't be working on it and certainly not live. In addition, as qualified electricians, if we wanted to be sure the power was disconnected wouldn't we insert a tester into each receptacle to insure the disconnect ?
    There are millions of not handle tied MWBCs in use right now operating safely. From Edison till 2008 we had MWBCs without handle ties. Worst code change ever.
    Again, well stated.

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