Multi-wire branch circuits

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sharan

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Do you have to run separate neutrals in a multi-wire branch circuits to avoid 2pole or 3 pole breakers?
 
roger3829 said:
If you ran seperate neutrals, it wouldn't be a MWBC
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Yes, if you had one neutral per circuit you could use single pole CB's without handle ties or multi-pole CB's. As Roger said that would no longer be a MWBC.
 
Yes, you would have to have a neutral for every hot! Imagine a multi-wire 277V circuit. Say you have a ballast short to ground and that 3-pole breaker opens. How many lights will go out?? I think it's a bad code rule... and then, out of all those lights, which one has the faulted ballast. I think I will be pulling a lot of neutrals in the future. Sad.. I believe they are doing this because some might be getting hurt opening a neutral?? THEY SHOULD KNOW BETTER.
 
bobsherwood said:
Yes, you would have to have a neutral for every hot! Imagine a multi-wire 277V circuit. Say you have a ballast short to ground and that 3-pole breaker opens. How many lights will go out?? I think it's a bad code rule... and then, out of all those lights, which one has the faulted ballast. I think I will be pulling a lot of neutrals in the future. Sad.. I believe they are doing this because some might be getting hurt opening a neutral?? THEY SHOULD KNOW BETTER.
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Why not install handle ties on single-pole breakers instead?
 
480 Sparky, Either way, if one circuit developes a fault, all 3 go off. I do maintence at a university.. a bunch of class rooms would go dark.. NOT GOOD! So far, University Park (the city having jurisdiction) has not adopted the 08 code but, the state of Texas has. I am going NOT do this for as long as I can. I just do not agree it's a good thing.
 
bobsherwood said:
480 Sparky, Either way, if one circuit developes a fault, all 3 go off. I do maintence at a university.. a bunch of class rooms would go dark.. NOT GOOD! So far, University Park (the city having jurisdiction) has not adopted the 08 code but, the state of Texas has. I am going NOT do this for as long as I can. I just do not agree it's a good thing.
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Using a handle tie with single pole breakers would not cause all three breakers to trip during a fault condition. Only a 3 pole breaker with an internal common trip mechanism would cause all three breakers to trip.

Chris
 
oh really? Okay, I thought that the one breaker going to the trip position would move the other breakers enough that they would also turn off?? I don't or have not ever used ties on breakers but, I did think that was the purpose if a tie if your load was say a 3 phase motor?? Ya learn something everyday.
 
raider1 said:
Using a handle tie with single pole breakers would not cause all three breakers to trip during a fault condition. Only a 3 pole breaker with an internal common trip mechanism would cause all three breakers to trip.

Chris
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Although that's not their intended design function I would think that there is a pretty good chance that more than one SP CB would trip with a handle tie especially if three breakers were handle tied and the one in the middle tripped. Has anyone ever tested this?
 
infinity said:
Although that's not their intended design function I would think that there is a pretty good chance that more than one SP CB would trip with a handle tie especially if three breakers were handle tied and the one in the middle tripped. Has anyone ever tested this?
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The trip mechanism for a circuit breaker functions independent of the movement of the handle. For example if you install a breaker lock to lock a circuit breaker in the on position the handle will not move, but it will trip in a fault condition.

For a circuit breaker to be turned off without the breaker tripping due to a fault would require the handle to be moved to the off position.

Chris
 
bobsherwood said:
oh really? Okay, I thought that the one breaker going to the trip position would move the other breakers enough that they would also turn off?? I don't or have not ever used ties on breakers but, I did think that was the purpose if a tie if your load was say a 3 phase motor?? Ya learn something everyday.
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2- and 3-pole breakers have an internal common trip. It is this mechanism that turns off all the power. Handle ties installed in SP breakers will not cause both or the other two to turn off if one trips.

From EC&M magazine:
Handle ties provide an acceptable method of linking operating handles of several single-pole circuit breakers together so they'll switch the tied circuit breakers together. Although good reasons exist for using handle ties, such as in multiwire branch circuits, the method in which a handle tie functions is often not well understood. And in some cases, application of handle ties may lead to unnecessary hazards.
It's important to understand the difference between the handle tie feature and the common trip feature. Handle ties fasten the handles of two or more single-pole circuit breakers together. With handle ties installed, all of the poles are switched on and off together. However, if one pole trips because of an overload or short circuit, the handle tie doesn't cause the connected poles to trip. The condition can leave one pole tripped and the other tied poles energized.
Multipole circuit breakers with common trip will switch all poles on and off together. They'll also trip all poles simultaneously when an overload or short circuit occurs on any of the poles. In this case, all poles operate together regardless of whether the circuit breaker is switched manually or opens automatically because of overcurrent.
It's often impossible to determine the difference between the common trip 2-pole circuit breaker and two single-pole circuit breakers with handle ties unless you're familiar with the product design. The potential hazard arises when one pole trips and another pole remains energized. It's especially hazardous if someone assumes that all poles are tripped and open when only one pole is open.
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iwire said:
Regardless of the trip free design IMO it is a roll of the dice if the tripping of one will take out the one beside it.
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That's my feeling as well. How many times have you just touched the handle of a CB and had it turn off. :rolleyes:
 
iwire said:
Regardless of the trip free design IMO it is a roll of the dice if the tripping of one will take out the one beside it.
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infinity said:
That's my feeling as well. How many times have you just touched the handle of a CB and had it turn off. :rolleyes:
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It may be possible for a handle tied single pole circuit breaker to cause the handle of an adjacent tied breaker to move to the off position, but I doubt that it would be a common occurrence.

Chris
 
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