multiwire branch circuits

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Re: multiwire branch circuits

Originally posted by a.wayne3@verizon.net:
In a perfect world yes this argument would hold water.But this is not a perfect world and unqualified personell do work all the time.To me the reason for yhis requirement is to prevent accidential shock to even a quote quallified person.
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It does prevent accidental shock when the circuits are on the same yoke because handle tyes are required by code and it kills both ungrounded conductors and eliminates any return current on the neutral for these circuits at the panel which can be disconnected at the receptacle or at the panel with no danger,But,it does not prevent accidental shock when the ungrounded conductors are not on the same yoke because the code does not require handle tyes and if both ungrounded conductors are not disconnected there can be return voltage and or current at the neutral if the neutral is disconnected at the panel and either circuit has something running on it which is a shock hazard.I guess they didn't take into consideration the return voltage on the neutral.
 
Re: multiwire branch circuits

I have always thought that a multi wire branch circuit should be protected by a 2 pole breaker regardless of the circuits feeding the same yoke or not. This is because I have seen situations where the two breakers have been mistakenly installed to allow both on the same pole. This creates the situation of overloading the neutral by as much as double the ampacity of the conductor. By requiring a 2 pole breaker this would be prevented. Even if a separate load might be de energized because of a 2 pole breaker should not be a concern, as long as the circuit is not essential for life safety. This would be in lines with 90.1b of the code.
 
Re: multiwire branch circuits

I have always thought that a multi wire branch circuit should be protected by a 2 pole breaker regardless of the circuits feeding the same yoke or not- - - -I have seen situations where the two breakers have been mistakenly installed to allow both on the same pole
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Should there be even more rules that make the installed system less convenient for the customer, to cover all of the other mistakes that an un-qualified, would-be electrician, could possibly make?

Ed
 
Re: multiwire branch circuits

By Jap2525:
the shock potential still exists if the neutral is disconnected in the panel from the load on circuit B.
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Of all the energized stuff in a breaker panel you're gonna focus on this?

How is the neutral you mention above different from every other neutral in the panel?

I don't treat anything in a breaker panel as if it's not energized. I've also never been lit up in a panel. Maybe that's why. (It could also be luck)
 
Re: multiwire branch circuits

That's my point,I don't worry about it,but the code seems to make a big issue about it.I think its useless to have to provide handle tyes for 2 circuits on the same yoke,If this rule is in fact for safety from getting shocked.It doesn't cover safety from shock on a multiwire circuit that is not on the same yoke,if you are dealing with the neutral,so why have it? why dont they just make it a violation to install 2 circuits on the same yoke instead? we could always install 2 individual receptacles instead of one and forget the same strap rule or having to tye the handles together.
 
Re: multiwire branch circuits

If a range had a fault to the chassis would you:

A: Remove only one pole leaving the other energized.

B: Remove both poles.

C: Do the Hokie Pokie.

[ October 15, 2004, 01:09 PM: Message edited by: physis ]
 
Re: multiwire branch circuits

how often do you use 2 single pole breakers for a 240v branch circuit to a range?
 
Re: multiwire branch circuits

Are you saying handle ties are required across two single pole breakers somewhere?
 
Re: multiwire branch circuits

no,I'm just talking about 120v duplex receptacles where the tab can be broken not 240v receptacles.But I guess in reply to your question if only qualified people are to be working on electrical ,like everyone states, what would be wrong with the fault in the range only tripping one phase as long as it tripped? I could trouble shoot it and where would the danger be to the HO if the 1 faultedcircuit tripped?
 
Re: multiwire branch circuits

In that instance I think it's a multiwire circuit. I'm thinking of single yoke as 220 receptacle. Why didn't you just say so.

And you don't really want to leave your faulted range energized do you?
 
Re: multiwire branch circuits

sorry I should have clarified my original post to say 125v duplex receptacle outlets not 240v outlets.
by energized you mean leave half of the power still on to the range even though the 1 circuit faulted and tripped don't you? No,your 240v heating elements wont work but it wouldnt hurt anything,this happens a lot on old fuse panels where 1 fuse blows and the other doesnt.
 
Re: multiwire branch circuits

If a range had a fault to the chassis would you:

A: Remove only one pole leaving the other energized.

B: Remove both poles.

C: Do the Hokie Pokie.
 
Re: multiwire branch circuits

Which brings up another interesting point.Is it a code violation to install a 120v or 240v multiwire branch circuit and land it on a receptacle from a fuse panel? I would say yes.if it serves more than one piece of equipment.

[ October 15, 2004, 02:01 PM: Message edited by: jap2525 ]
 
Re: multiwire branch circuits

and on the range receptacle it is still only servicing one device or one piece of equipment even though there are 2 circuits to the receptacle.I feel this is a different situation.
 
Re: multiwire branch circuits

Originally posted by physis:
And you don't really want to leave your faulted range energized do you?
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Actually this would be fine.

For a range or dryer on a single phase house service all you need is handle ties, you do not need an internal common trip breaker.

If you use the handle ties and phase "A" trips from a fault there is a very good chance that phase "B" will still be live.

What difference would this be from a range or dryer fed from fuses? :)

[ October 15, 2004, 04:49 PM: Message edited by: iwire ]
 
Re: multiwire branch circuits

Originally posted by jap2525:
Is it a code violation to install a 120v or 240v multiwire branch circuit and land it on a receptacle from a fuse panel? I would say yes.if it serves more than one piece of equipment.
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Why?

210.4(B) Dwelling Units. In dwelling units, a multiwire branch circuit supplying more than one device or equipment on the same yoke shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originated.
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Notice it makes no mention of breakers only that means to disconnect simultaneously all ungrounded conductors at the panelboard shall be provided.

A two pole switch at the panel would accomplish this in my opinion. :)
 
Re: multiwire branch circuits

there is no need,a range receptacle and a dryer receptacle,or welder receptacles are not more than one device on a yoke,they are individual receptacles (device) on a single yoke. A range receptacle is not more than one device on a single yoke,it is one device on a single yoke.Unlike a duplex receptacle where if you break the tab you then have (2) seperate useable devices.You cannot seperate a range or dryer receptacle and have 2 working devices,if seperated you only have one device that cannot do it's job.
 
Re: multiwire branch circuits

Originally posted by physis:
It's because on a two pole circuit that kicks the breaker you want both hots removed.
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You can want this, but it is not an NEC requirement. :D
 
Re: multiwire branch circuits

Posted by Physis yesterday:

The second circuit would have An ungrounded and potentially energized conductor connected but there would be no hazard I can see.
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I'm sure we agree Bob, but do you want to take the quiz.
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