The new 2008 NEC code 210.4(B)

[powersoft]

The new 2008 210.4 reads:
210.4 Multiwire Branch Circuits.
(B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.
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My understanding:
For shared neutrals in conduits, all branch circuits shall have disconnecting means via a multipole breaker in the panel it serves from, reguardless of how many poles.

What if the wires go through a wiring trough or a chase nipple? There are no exceptions. Has this ever been disussed here before?

 

[roger]

Has this ever been disussed here before?

Many times. Do search for MWBC, handle ties, 210.4 etc...

Roger

 

[augie47]

Let's define you understanding a bit..
Check the definitions for "branch circuit, multiwire".
If the circuit qualifies then there must be a common disconnecting means.
This can be a multi-pole breaker, a handle tie on the circuits involved or another means.

The rule would apply to the individual MWBC. If you happen to have multiple MWBs in one conduit, each would be addressed separately.
(For example, you would not need a 6 pole handle tie for (2) MWBC)

 

[powersoft]

Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.


I assume this is because it is in the same condult or jacket. Still no clear cut definition if that includes a wiring trough or chase nipple (in the case of 6" nipple which can feed an adjacent panel). This could be a real problem with AHJ and contractors it seems.

 

[iwire]

I assume this is because it is in the same condult or jacket. Still no clear cut definition if that includes a wiring trough or chase nipple (in the case of 6" nipple which can feed an adjacent panel). This could be a real problem with AHJ and contractors it seems.

Huh? I have no idea what you mean.

 

[roger]

My understanding:
All hot wires that are routed in a common conduit, trough (or nipple) shall be protected by a multipole breaker, no matter how many poles are required to accomplish this.

Go back and read Augie's post again.

Roger

 

[charlie b]

I assume this is because it is in the same condult or jacket.

You assume incorrectly. The reason that a common trip (multipole breaker or handle ties) is required has to do with the safety of a maintenance person working in a junction box somewhere along the run. It does not matter whether the wires are run in conduit, in surface mounted raceway, as a multi-conductor cable, or any thing else.

 

[powersoft]

Let's define you understanding a bit..
Check the definitions for "branch circuit, multiwire".
If the circuit qualifies then there must be a common disconnecting means.
This can be a multi-pole breaker, a handle tie on the circuits involved or another means.

The rule would apply to the individual MWBC. If you happen to have multiple MWBs in one conduit, each would be addressed separately.
(For example, you would not need a 6 pole handle tie for (2) MWBC)

Sorry my typeing and my reading are getting a little stretched.

I guess what really gets me is a staff note i read from necplus.com
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Staff Note for 210.4(B)
Multiwire branch circuits are frequently used to economize on homerun wiring by sharing a grounded conductor among either two or three phase conductors. For safety, 210.4(B) requires that when a multiwire branch circuit supplies more than one device or equipment on the same yoke (often a duplex receptacle), a multipole circuit breaker or switch or two circuit breakers with a listed handle tie must be used to disconnect all ungrounded conductors. The reason for this requirement is to prevent injury to electricians or others servicing those devices by ensuring that all conductors in the same outlet box are OFF (de-energized).
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Is this the consensus then is a ungrounded wire of a MWBC is anything surounded in a jacket, box or other wiring means beside the panelboard box that serves BESIDES a shared neutral???

 

[augie47]

Seems like you are trying to reinvent the wheel
Again, the definition:
Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.
No mention of "jacket, cable,box, etc.
If you have a circuit with more than one ungrounded conductor and a shared grounded condutor and it meets the above definition, you have a MWBC.
One that is determined, you need a common disconnecting means for the ungrounded circuits. Makes no difference if they are in a cable, pipe, or free air.
The "same yoke" rule was prior to the '08 Code whicjh expanded the requirement.

 

[LarryFine]

PS, welcome to the forum!

The handle-tie or multi-pole breaker requirement is for each group of two or three hots that share a neutral. For example, a 3-wire (two hots and a neutral) MWBC requires a 2-pole breaker or handle tie.

Even if two of these 3-wire MWBC's happen to enter the same cable or conduit, each pair of hots that share a neutral must still only have the two poles of each MWBC joined at the handles, nothing more.

 

[Split Bolt]

And let's not forget AFCI protection, if applicable. That would rule out the use of handle ties and you would NEED a 2-pole AFCI breaker.

 

[Dennis Alwon]

And let's not forget AFCI protection, if applicable. That would rule out the use of handle ties and you would NEED a 2-pole AFCI breaker.

Actually, as mentioned in an earlier thread, GE now makes single pole afci that can be put together and will work on a MWBC. You would use handle ties in that case.

Here is the GE email I received.

As you may or may not know, we have a branch/feeder 2 pole shared neutral AFCI but not in the new combination style. In addition, Siemens has a 2 pole shared neutral combination AFCI out in the marketplace. CH and Square D do not have a combination 2 pole device at this time.

With the new GE version 1 pole combination AFCIs, contractors can apply qty 2 - 1 poles with a handle tie to meet the shared neutral application. We are the only manufacturer that can apply combination AFCIs in this way. Siemens, CH, and Square D all use a ground CT in their AFCI detection which does not allow them to utilize this configuration.

This will be more cost effective than Siemens 2 pole combination AFCI.

The use of shared neutral circuits produces significant copper savings when two branch circuits are close to each other but far from the circuit breaker panel. A shared neutral circuit uses 3-conductor NM-B wire to join two adjacent circuit breakers in the panel to a junction box near the branch circuit loads/outlets. See attached publication for drawing on how this works.

 

[Split Bolt]

Actually, as mentioned in an earlier thread, GE now makes single pole afci that can be put together and will work on a MWBC. You would use handle ties in that case.

Here is the GE email I received.

Interesting. Thanks (again) Dennis! Can you put a link to the product? I'm curious as to how the neutral connects.

 

[Dennis Alwon]

Interesting. Thanks (again) Dennis! Can you put a link to the product? I'm curious as to how the neutral connects.

You are welcome again

Here is the link

 

[Split Bolt]

Just checked-out the link. (I'm going to stop thanking you so much...people may talk!) I'm still not clear on the concept. If circuit 1 (black) goes to the first breaker with the neutral, I'm OK there. It's circuit 2 (red) that bothers me. If the neutral of the MWBC doesn't connect to that breaker, how is AFCI #2 going to sense an arc fault between the red and neutral? Maybe I'm missing something!

 

[cadpoint]

Just checked-out the link. (I'm going to stop thanking you so much...people may talk!) I'm still not clear on the concept. If circuit 1 (black) goes to the first breaker with the neutral, I'm OK there. It's circuit 2 (red) that bothers me. If the neutral of the MWBC doesn't connect to that breaker, how is AFCI #2 going to sense an arc fault between the red and neutral? Maybe I'm missing something!

Please just recall that in most all cases one will always "Breaker" a circuit...

Apply #1(thoughts) to be the same as to #2, the noodle will always have to be there to complete the circuit. If there's no path, there's no difference in potentional energy!

Now, also recall that the noodle will only see the amount of the unbalanced loads that Might / or might not exist between the two circuits...

Now to make a simplied statement the AFCI is a type of a "breaker", it still has the mechanic's of a typical breaker in it, and with the sense to a limit draw of mA, (milliamps) and not go above before it releases...

The code address's the application of the MBWC because of the spared neutral yes, and the measurable amount is mentioned above.

Just think of it as how does one "Breaker" the MWBC!

 

[glene77is]

Here is the link

Dennis,
Thanks for the link.

This is a rhetorical observation, and I do not expect an answer.
(1) I see that #1 CB passes the neutral through to the neutral bar.
(2) I see that #2 CB has contact with the neutral at the neutral bar.
(3) If #2 CB does not require a neutral internally,
then why does #1 CB require one. Both CB should work the same way.

So,
(4) Why not just pass the neutral around all the AFCI combo CB
straight to the neutral bar ? Let them both compare to the neutral bar!

Perhaps Gar or Mivey will have something to say on this.

 

[cadpoint]

I don't see, it based on GE's own statement - Theory on... GE made a point not to use the noodle...

Besides, is that noodle isolated to a side of AFCI, I'll say not...

 

[Dennis Alwon]

Dennis,
Thanks for the link.

You're welcome also. Here is the link to the other thread on this matter. Apparently GE has done away with GFCI protection in their AFCI breakers.