Inspecting multiwire circuits in the panel

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raider1 said:
Yes,

210.4(B) Disconnecting Means. Each multiwire branch circuit shall
have a means to simultaneously disconnect all ungrounded
conductors at the point where the branch circuit originates.

Chris
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Now thats one very stupid idea.So if one circuit trip for what ever we shut the others down.I see some really upset office people.Just why did they want to do this ? A real electrician was never in danger.
 
Jim W in Tampa said:
Now thats one very stupid idea.So if one circuit trip for what ever we shut the others down.I see some really upset office people.Just why did they want to do this ? A real electrician was never in danger.
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True, but a hack may open one breaker, and then open the neutral in a junction, and get between the neutral line and load.

What bothers me is, the inspectors here used to require handle ties, and now they don't. So it seems it's going to be required after all. I'm so confused. :confused:
 
Dan Smith said:
With red and black conductors running all over the place in some panels
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Black on one phase, red on the other wasn't good enough?

And this handle tie thing is getting on my nerves, I get entirely too many inspectors that I have to force to read that one out loud - and then I have to ask them if they know what a "yoke" is...

I hope my state either skips the '08 cycle or uses some common sense.
 
Could it be that the CMP wasn't trying to make or life difficult but maybe trying to protect a happy ho who had nothing to do one saturday and wanted to play electrican.
 
Now I am going to stir the pot here....Just for the record I do not do multi wired branch circuits and have a dislike for them...I have seen where you could weld the inside of the outlet off and not trip the double pole breaker...I have seen 240V heaters added to the circuit cause it is on a double pole. we recently rewired an entire commercial kitchen that was MWB...the circuit breaker failed to trip and toasted a 5k Stainless frig.. I have no time for MWB as long as 2 pole breakers are used and not handle ties...and can any tell me why using handle ties you would have a safer operation than on a two pole breaker? I have seen many fail and at the cost to the customer but yet where handle ties are used less failure...I am clueless here, I thought the 2 pole breaker worked the same as a single pole....
 
cschmid,
How does the breaker not tripping have anything to do with the fact the circuit was a multiwire branch circuit?
Don
 
good point... I just have found a higher incident in breaker failure on MWB... probablly just my luck of coincidence... I call it breaker failure but it is equipment damage on MWB that I see and I associate it with breaker failure...
 
cschmid said:
Now I am going to stir the pot here....
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OK....your choice. :grin:


Just for the record I do not do multi wired branch circuits and have a dislike for them...
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Electrically they behave like every service or feeder that you have ever worked with.

I have seen where you could weld the inside of the outlet off and not trip the double pole breaker.
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Yes, and I have seen it with single pole breakers.

Can you think of any electrical reason why the breaker would behave differently?

..I have seen 240V heaters added to the circuit cause it is on a double pole.
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And that is a problem?

The NEC allows supplying both 120 and 240 volt loads with one circuit.

Happens all the time with electric ranges, electric dryers, services and feeders.

we recently rewired an entire commercial kitchen that was MWB...the circuit breaker failed to trip and toasted a 5k Stainless frig..
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I doubt that MWBC was the actual problem, there may well have been miss-wiring.

I have no time for MWB as long as 2 pole breakers are used and not handle ties...
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No time....;) MWBCs save me time and money, they also use less copper. Many times a MWBC will waste less power due to voltage drop.

and can any tell me why using handle ties you would have a safer operation than on a two pole breaker?
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One circuits failure will not take out one or two more circuits.

I have seen many fail and at the cost to the customer but yet where handle ties are used less failure...I am clueless here, I thought the 2 pole breaker worked the same as a single pole....
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They do work the same. Maybe just the luck of the draw you ran into some bad ones.

When I get prints the first thing I will do if allowed by job specs is layout as many 3 circuit net work home runs as I can, they are simply more efficient and make a huge difference with the number of current carrying conductors in a raceway resulting in much less derating then all two wire circuits would require.
 
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Awg-Dawg said:
This one seems like it will be a PITA.
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I agree. A big one!! Let's hope and try to get this changed back for the 2011 cycle. Think we can? It's not even in effect yet and so many of us don't like/agree with this one.
 
Maybe this one will cause a huge uproar when the 2008 hits the public. I sure hope so. This is just another issue used to drive the extra cost of multi-pole CB's and handle ties.
 
Bob I can not even offer a rebuttal to that.. I understand all the cost effectiveness from a EC's point of view..so I wish you all a happy labor day weekend and I will check in on Tuesday..
 
infinity said:
Maybe this one will cause a huge uproar when the 2008 hits the public. I sure hope so. This is just another issue used to drive the extra cost of multi-pole CB's and handle ties.
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In my opinion, it has nothing to do with buying more multipole breakers or handle ties...I think it has everything to do with the copper manufacturers selling more wire because people will stop using MWBCs. There are too many design issues with using them now that this change has passed. I keep thinking about a MWBC feeding 277V troffers. What is that, about 60 lights or so on the MWBC? If that circuit goes down, the designer is going to have an angry client...
 
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ryan_618 said:
In my opinion, it has nothing to do with buying more multipole breakers or handle ties...I think it has everything to do with the copper manufacturers selling more wire because people will stop using MWBCs. There are too many design issues with using them now that this change has passed. I keep thinking about a MWBC feeding 277V troffers. What is that, about 100 60 lights or so on the MWBC? If that circuit goes down, the designer is going to have an angry client...
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You might be right but personally unless the spec tells me otherwise, I will still use them and install a handle tie. If the customer has a problem with 3 circuits tripping at once he can take out a screw driver and remove the handle ties.

If there is an angry client involved think how he'll feel when the job now uses all two wire circuits that costs him a lot more money. Using MWBC will still save the guy installing the circuits (me) money even if he has to use a MP CB or a handle tie.
 
I'm really starting to dislike the NEC. All of these things that have been safe for so long are now being made to protect the lowest common denominator. How nice. :rolleyes:
 
peter d said:
I'm really starting to dislike the NEC. All of these things that have been safe for so long are now being made to protect the lowest common denominator. How nice. :rolleyes:
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I know pretty soon they have it so anyone can do electrical work :(
 
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