2008 and Multiwire Branch Circuits

[76nemo]

Moderator Note. This was moved from another thread to avoid a thread jack.

One way to get there is to work on a MWBC, to turn off the breaker that serves the load you are working on but not turn off the other breakers that share the same neutral wire (not allowed in 2008 NEC,

Charlie, I have yet to look at the '08. What is the comment you make on MWBC's? It sounds as if you are saying they are no longer permissable???

 

[iwire]

Charlie, I have yet to look at the '08. What is the comment you make on MWBC's? It sounds as if you are saying they are no longer permissible???

Every MWBC must have a common means of disconnect.

So handle ties or common trip breakers must be used.

This really messes with me as I would have them all over the panel. For example circuits 1, 4 and 41 could be one of my MWBCs. That has to stop unless I can find an approved handle tie for that. :grin:

 

[charlie b]

Charlie, I have yet to look at the '08.

Consider yourself lucky.

What is the comment you make on MWBC's? It sounds as if you are saying they are no longer permissable???

The 2008 requires that a MWBC be served by a common 2-pole (or 3-pole) breaker, or with single pole breakers that have their handles tied together in some fashion. When you turn off one phase supply to a MWBC, the power from all other phases must go off also. That would prevent power from one breaker from posing a hazard, when you are working on a load served by another breaker.

 

[76nemo]

Every MWBC must have a common means of disconnect.

So handle ties or common trip breakers must be used.

This really messes with me as I would have them all over the panel. For example circuits 1, 4 and 41 could be one of my MWBCs. That has to stop unless I can find an approved handle tie for that. :grin:

Thanks Bob, I have to pick up an '08. Good luck on THAT handle tie:grin:

 

[76nemo]

Consider yourself lucky.

The 2008 requires that a MWBC be served by a common 2-pole (or 3-pole) breaker, or with single pole breakers that have their handles tied together in some fashion. When you turn off one phase supply to a MWBC, the power from all other phases must go off also. That would prevent power from one breaker from posing a hazard, when you are working on a load served by another breaker.

Oooookay, I am sticking my neck out here, leading myself to slaughter. I like the idea, quite a bit actually. I do not want to hijack the thread with this. Can one of the moderators possibly move this to another thread in this chapter?

 

[iwire]

The 2008 requires that a MWBC be served by a common 2-pole (or 3-pole) breaker, or with single pole breakers that have their handles tied together in some fashion.

If we get right down to it I believe a 2 or 3 pole switch located at the panel would meet the NEC as well but that is costly way to go.

I am shooting from the hip, my 2008 is out in the truck. :smile:

 

[peter d]

This was clearly an underhanded victory for Copper.org's campaign to eliminate MWBC's. :roll:

 

[480sparky]

....This really messes with me as I would have them all over the panel. For example circuits 1, 4 and 41 could be one of my MWBCs. That has to stop unless I can find an approved handle tie for that. :grin:

If you build it, Arlington will sell it.

 

[iwire]

If you build it, Arlington will sell it.

You are probably right. :grin:

 

[George Stolz]

I'm gonna just handle-tie the whole panel together, then I won't have to worry about it.

 

[480sparky]

I'm gonna just handle-tie the whole panel together, then I won't have to worry about it.

Shoot! Does the two-pole main count? :grin:

 

[LarryFine]

I'm gonna just handle-tie the whole panel together, then I won't have to worry about it.

Sure! A couple of 20-pole handle-ties and you're all set. :grin:

 

[480sparky]

Sure! A couple of 20-pole handle-ties and you're all set. :grin:

What happens when the new 80-plus space panels hit the market? I cna't even imagine a 40-pole handle tie! Tim Taylor would be proud of it!

 

[infinity]

It's been mentioned before and is worth mentioning again. This idea of shutting off all of the circuits of a MWBC at one time will make it more likely that someone will work on circuits that are energized. Shutting off one circuit to work on it may be tolerable, shutting off three at once may not.

 

[roger]

It's been mentioned before and is worth mentioning again. This idea of shutting off all of the circuits of a MWBC at one time will make it more likely that someone will work on circuits that are energized. Shutting off one circuit to work on it may be tolerable, shutting off three at once may not.

And that is the truth of the matter.

I know I'll continue to use MWBC's and our people as well as the maintenance people out there will be working on these circuits hot since it will be to much of an inconvenience to turn them all off.

Roger

 

[iwire]

And I also agree with Roger and Rob.

In the world of text and paper it sounds like an increase of safety.

Out in the real world it will mean people will be less likely to de-energize the single circuit they are working on because often they will not be allowed by building occupants or will not choose to shut off the other one or to circuits.

 

[cschmid]

when someone dies the MWBC will be eliminated..yet if installed correctly on lighting systems with quick disconnects should never be issue..until a ballast shorts out and takes down the whole place and the manager will want that fixed so it does not happen again..the first down time due to lighting fault and MWBC will be eliminated..so when designing consider the lost production from a blowen lighting circuit when it shuts down the who room and the operatoers hit the E-stops for safty reasons..

 

[iwire]

when someone dies the MWBC will be eliminated...

I am sure people have been killed by working with MWBCs, I am sure people have been killed working with two wire circuits.

I doubt electricity will be eliminated anytime soon.

 

[cschmid]

I agree electricity will not be eliminated..with the increased demand were is all the electricity going to come from..oh that right that funny little receptacle in the wall..

 

[roger]

when someone dies the MWBC will be eliminated..

And when there is finally a fatal car wreck cars will be eliminated, wait, hasn't that already happened, yet there are still cars out there. :-? :wink:

IOW's, don't hold your breath waiting for MWBC's to go away.

Roger