Multiwire branch circiuts

[Will Wire]

If the ungrounded conductors on a multiwire branch circuit do not supply more than one receptacle on the same yoke, is it requried to disconnect simultaneously all the hot conductors at the panelboard where the circuit originates? If the multiwire circuit is split in a junction box without a device.
Thank you.

 

[crossman]

In the 2008 NEC it is required.

210.4

 

[cloudymacleod]

If the ungrounded conductors on a multiwire branch circuit do not supply more than one receptacle on the same yoke, is it requried to disconnect simultaneously all the hot conductors at the panelboard where the circuit originates? If the multiwire circuit is split in a junction box without a device.
Thank you.

by the 2008 code all mwbc has to be disconnected simultaneously now, eithier it's on the same yoke or not.

 

[mdshunk]

by the 2008 code all mwbc has to be disconnected simultaneously now, eithier it's on the same yoke or not.

In resi, MWBC's are going to pretty much disappear anyhow. For non-dwelling work, I'll be interested to see what installation standard develops in the industry. I'm not sure many commercial property owners and tenants would tolerate simultaneous disconnection, so a neutral for every conductor might be a more tolerable (if not more expensive) solution.

 

[cschmid]

I do believe this is the begining of the end for MWBC..

 

[roger]

For non-dwelling work, I'll be interested to see what installation standard develops in the industry. I'm not sure many commercial property owners and tenants would tolerate simultaneous disconnection, so a neutral for every conductor might be a more tolerable (if not more expensive) solution.

I see handle ties being removed, switches installed somewhere upstream of the loads so the individual ungrounded conductors can be isolated, violations of hot work, etc...

With the price of copper continuing to rise, MWBC's will not be abandoned.

Roger

 

[cschmid]

Copper poor mans gold..I do not see customers being happy with opening 2 circuits or loosing entire areas of lights..Bad for business and good for law suits..we only install were necessary now..otherwise we do not install or design with them now..Yes we are still in business and doing okay..

 

[roger]

or loosing entire areas of lights..

Being that your example would most likely be for fluorescent fixtures, 410.73(G) (2005) will make your concern a non-issue.

Roger

 

[Buck Parrish]

We can still put the dish washer and disposal on a 14-3- not much of a help, Ha . Still got to have a two pole breaker. But only one neutral.

My question is are the distributors going to start making some sort of handle ties that we can tie single pole breakers together? Or will they actually be two or three pole breakers required ?

 

[roger]

My question is are the distributors going to start making some sort of handle ties that we can tie single pole breakers together?

Buck, they have been available for ages.

Roger

 

[augie47]

Buck, they have been available for ages.

Roger

Roger,
It has been my understanding that they are not going to market a 3 pole handle tie.
Factory rep tells me that can't assure all three breakers will trip and folks might use these for a 3 pahse circuit..
Old age tells me they want to sell more 3 pole breakers.

 

[roger]

Roger,
It has been my understanding that they are not going to market a 3 pole handle tie.
Factory rep tells me that can't assure all three breakers will trip and folks might use these for a 3 pahse circuit..
Old age tells me they want to sell more 3 pole breakers.

Augie, Square D makes a handle tie for three breakers, model # QO3HT.

There is not a requirement for a fault to open all three breakers so it doesn't have to operate as a "common trip", the requirement is that all ungrounded conductors will be "disconnected" at the same time meaning, if the handles are pushed (by hand) to the off position they will all go together.

However, I wouldn't doubt your last sentence is not true.

Roger

 

[crossman]

Being that your example would most likely be for fluorescent fixtures, 410.73(G) (2005) will make your concern a non-issue.

What if you are adding more luminaires to the circuit itself? What if one lighting circuit shorts, and it shuts off three circuits simultaneously? What if you are removing a luminaire from the circuit, maybe the CEO wants to replace the standard lay-in 2x4 with a gold-plated mega-buck model? There are still plenty of issues here.

To me, the solution in the 2008 NEC is more dangerous than the previous hazard!

 

[augie47]

Augie, Square D makes a handle tie for three breakers, model # QO3HT.

There is not a requirement for a fault to open all three breakers so it doesn't have to operate as a "common trip", the requirement is that all ungrounded conductors will be "disconnected" at the same time meaning, if the handles are pushed (by hand) to the off position they will all go together.

However, I wouldn't doubt your last sentence is not true.

Roger

Roger, I stand corrected. For what it's worth it wasn't a sqaure D rep
His reference to "common-trip", I believe, was in regard to using the "tie" as a 3 phase (ie: motor) disconnect. I did notice on the directions for the
QO3HT they pointed out it was not to be used for 3 phase or common trip applications.

 

[peter d]

With the price of copper continuing to rise, MWBC's will not be abandoned.

I think you're right about that, but I certainly don't like any of these NEC rules that may cause an electrician to think twice about installing a MWBC.

 

[JohnJ0906]

I think you're right about that, but I certainly don't like any of these NEC rules that may cause an electrician to think twice about installing a MWBC.

I rather like 210.4(D) (grouping grounded and ungrounded conductors from each MWBC.)

 

[peter d]

I rather like 210.4(D) (grouping grounded and ungrounded conductors from each MWBC.)

So do I.

 

[cschmid]

I know better then this..because the MWBC is some what of a money safer in the up front costs of the install..I do believe though as time goes by and electrical costs increase maintenance personal do more and more work on electrical..My wife works for the government and their budgets are tight..there maintenance men also do the janitor work..they even run electrical wiring..

I am telling you it is wild..they move cubicles around and the maintenance people do it all..So they were having some computer problems and they had a contract with this computer company and the companies solution was to have the employees to spray the carpet with water to control the static..I finally told them to fix the grounding problem they had with the improperly run AC cable they were using..I explained it to them (maintenance supervisor) and the maintenance guys went and fixed it..they fired the computer company they used for servicing their computers..

Now I am telling you guys that no matter how many laws you pass and how many rules you have the under qualified are going to do electrical work..the rules are all about the safety of the under qualified and the non qualified..I really do believe that the MWBC are going to become a thing of the past..

I do understand the feeling about unqualified and under qualified but the regulations are to protect the unqualified..it is all about the safty..I have talked to the inspector about the issue but you know the drill and as long as they do the contractors on new installs..

I am not promoting the unqualified just know it exsistes and it is not going away..No delusions here..

 

[electricmanscott]

My wife works for the government and their budgets are tight....

:grin: :grin: :grin:

 

[dnem]

I do believe this is the begining of the end for MWBC..

In resi, MWBC's are going to pretty much disappear anyhow. For non-dwelling work, I'll be interested to see what installation standard develops in the industry. I'm not sure many commercial property owners and tenants would tolerate simultaneous disconnection, so a neutral for every conductor might be a more tolerable (if not more expensive) solution.

Right now Ohio is doing the '05, '08, '05 flipflop for 1,2,+3 family. . The projects that are on '08 [Jan,Feb,March app for plan review] most often have MWBC with handle ties [or 2 pole breakers] on kitchen, laundry, baths, unfinished basement, garage, + outside. . They have combo AFCIs on the rest of the house.

If MWBC disappear in residential under the '11 code cycle will be based on 2 things:
1] Will the NEC extend AFCIs to the remaining parts of the house [kitchen, laundry, baths, unfinished basement, garage, + outside] ?
2] Will the combo AFCI manufacturers [SquareD, Siemens, Eaton] change their decision about not developing multipole combo AFCIs that will allow unbalanced current on the neutral ?

"I'm not sure many commercial property owners and tenants would tolerate simultaneous disconnection, so a neutral for every conductor might be a more tolerable (if not more expensive) solution."

Commercial will stay "a mixed bag". . The decision to use dedicated neutrals will be based on price and input from the building owner. . For projects that are price only driven, shared neutrals will continue.

We'll also have to see how common it will be for those servicing the lights after occupancy to just pop off the handle ties. . Alot with be based on the exact manufacturing technique. . Will the handle ties pop off easily or will it be a big project ? . If quick pop off handle ties become standard procedure, we'll see MWBC remain common place.