Multi Wire Branc Circuits..

[xformer]

New for 2011, Section 200.4 states the neutral conductor can not be used for more than one branch circuit, one multiwire branch circuit, or for more than one set of ungrounded conductors. Can anyone give me an example of the neutral being used for more than one set of conductors and maybe a picture of such a violation?

 

[raider1]

Previously there was no NEC section that prohibited installing multiple ungrounded circuits of the same phase on a single neutral conductor provided that the neutral conductor was sized to carry the maximum load.

For example if I put to 20 amp circuits from the A phase on a neutral that neutral couls have a load of up to 40 amps because the amps on the same phase are additive. This section now makes it a code violation to do that.

Hope this makes sense.

Chris

 

[xformer]

Yes.. that makes sense. thank you for replying....

 

[Dennis Alwon]

Basically, as Chris mentioned, many believed if the neutral was sized for the load then whats the problem. So One neural sized as a #8 for 40 amps and 2 hots from the same phase. Technically that is not a MWBC, by definition, so handle ties were not necessary and one could do that. Not any more, but I don't think it was done very often.

 

[jumper]

I think 225.7(B) is what caused the new section to be added.

Or what Dennis posted.

 

[infinity]

This has been the accepted practice. Now it's clarified that it can only be done for outside circuits.

225.7 Lighting Equipment Installed Outdoors.
(A) General. For the supply of lighting equipment installed outdoors, the branch circuits shall comply with Article 210 and 225.7(B) through (D).
(B) Common Neutral. The ampacity of the neutral conductor shall not be less than the maximum net computed load current between the neutral conductor and all ungrounded conductors connected to any one phase of the circuit.

 

[hurk27]

I don't have a copy of the 2011, so I'm not sure how it's worded, but every branch circuit breaker in any panel shares one phase or the other with only one neutral?

 

[Dennis Alwon]

Here it is

200.4 Neutral Conductors. Neutral conductors shall not be used for more than one branch circuit, for more than one multiwire branch circuit, or for more than one set of ungrounded feeder conductors unless specifically permitted elsewhere in this Code.

 

[romex jockey101]

Basically, as Chris mentioned, many believed if the neutral was sized for the load then whats the problem. So One neural sized as a #8 for 40 amps and 2 hots from the same phase. Technically that is not a MWBC, by definition, so handle ties were not necessary and one could do that. Not any more, but I don't think it was done very often.

or just make shure that you use seperate phases and it will cancell out the load on the nuetral...thats y u can tuse a tandem breacker

 

[romex jockey101]

in conneticut we still use 2005 nec...what staes use 2011..and i dont see a problem if you use seperate phases for your hots so it cancels the load on the nuetral...if you use a tandem breaker and try this you can burn up the nuetral bc both legs would be on same phase

 

[480sparky]

in conneticut we still use 2005 nec...what staes use 2011..and i dont see a problem if you use seperate phases for your hots so it cancels the load on the nuetral...if you use a tandem breaker and try this you can burn up the nuetral bc both legs would be on same phase

Not all tandems are like that. Most are, but there are some that span 2 phases/legs.

 

[rich9112]

1950's homes

1950's homes

Basically, as Chris mentioned, many believed if the neutral was sized for the load then whats the problem. So One neural sized as a #8 for 40 amps and 2 hots from the same phase. Technically that is not a MWBC, by definition, so handle ties were not necessary and one could do that. Not any more, but I don't think it was done very often.

I still see this on occasion when changing/upgrading panels. It is not uncommon for homes built in the 1950's era to have 2 or 3 upsized neutrals with 4-5 circuits utilizing each neutral. It can make it very difficult to trouble shoot when the neutral is loose somewhere.

 

[mlnk]

In residential I stopped using multi-wire circuits 10 years ago. Who needs more requirements and more problems? For a small contractor the wire is more expensive. Also AFCI will not work on multi-wire circuits.

 

[480sparky]

In residential I stopped using multi-wire circuits 10 years ago. Who needs more requirements and more problems? For a small contractor the wire is more expensive. Also AFCI will not work on multi-wire circuits.

GE and Siemens both have 2-pole AFCIs.

 

[Dennis Alwon]

GE and Siemens both have 2-pole AFCIs.

Just to clarify that GE uses 2 sp afci with a handle tie as their dp AFCI. It is the only manufacturer that has it designed this way.

 

[gndrod]

Indicator

Indicator

Just to clarify that GE uses 2 sp afci with a handle tie as their dp AFCI. It is the only manufacturer that has it designed this way.

Hi Dennis,
There is a dual LED indicator on the Seimens 2p that shows which branch leg tripped. I am wondering if the single flag window on the GE does the same somehow?

 

[Dennis Alwon]

Hi Dennis,
There is a dual LED indicator on the Seimens 2p that shows which branch leg tripped. I am wondering if the single flag window on the GE does the same somehow?

I don't know but I guess you could remove the breaker tie and find out which circuit is the problem. I never run mwbc in homes.

 

[gndrod]

I don't know but I guess you could remove the breaker tie and find out which circuit is the problem. I never run mwbc in homes.

I havn't in resi either. Interesting answer for trouble shooting though. TX

 

[mlnk]

I stand corrected. But....Why limit yourself to GE or CH and to an unusual item that may be out of stock. My advise is: Avoid multi-wire circuits like the plague. Make life simple.

 

[al hildenbrand]

Why limit yourself to GE or CH and to an unusual item that may be out of stock. My advise is: Avoid multi-wire circuits like the plague. Make life simple.

Interesting question.

The new 2011 NEC 210.12(B) requirement to add AFCI to a branch circuit that has a "modification" will force us to have to add AFCI protection to existing legacy multiwire branch circuits (MWBC).

That is, unless we run all new wiring instead.

Or unless the local jurisdiction isn't enforcing 2011 NEC 210.12(B).

Or if manufacturers start selling AFCI receptacle devices.

The thing I like about the GE single pole combination type AFCIs is that there is no "GFI-like" component in its circuitry. The GE sp CAFCI is pure arc fault detection. When one hooks two GE sp CAFCI together on an existing MWBC (with handle tie), the MWBC neutral connects to only one of the breakers . . . doesn't matter which one.

Try that with any of the other manufacturer's single pole AFCIs and they will never hold.