Article 210.4(B) Clarification

[NECuser]

2011 NEC Section 210.4(B) states: "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." I received correspondence from another engineer indicating he interprets this to mean "All wires, which includes all hot and neutral wires, of a single wiring installation must be disconnected with one device (circuit breaker)...Simply stated, one neutral wire shall not service two circuits...Therefor, a 3 wire 120/240 or a 240/480 system shall not use 2 circuit breakers, one for each hot line because there is only one neutral". His recommendation proposed two alternatives; either use a separate neutral for each circuit or use a 2-pole circuit breaker. I disagree with his interpretation. My understanding is the neutral wire is not impacted by NEC 210.4(B) because the neutral wire is considered a grounded conductor. My proposed response is going to require installation of 2 single pole circuit breakers with identified handle tie [not a two-pole circuit breaker (in order to limit the number of lights that would turn off if maintenance needed to work on the circuit)]. Please confirm if my understanding that the neutral is not impacted by 210.4(B) is correct and my proposed response is feasible.

 

[augie47]

IMO, your thinking is in line with the NEC.
That said, most of the handle-ties I have seen will not easily facilitate turning off one breaker as you describe.
(If they did, it would pretty much defeat the intent of the Article)

 

[NECuser]

I just came across Article 225.7 (B) which states Common Neutral is permitted for Lighting Equipment Installed Outdoors. Thank you for your help.

 

[roger]

My proposed response is going to require installation of 2 single pole circuit breakers with identified handle tie [not a two-pole circuit breaker (in order to limit the number of lights that would turn off if maintenance needed to work on the circuit)]. Please confirm if my understanding that the neutral is not impacted by 210.4(B) is correct and my proposed response is feasible.

You are correct that 210.4 is addressing the "ungrounded conductors" and not the grounded conductor. Another way to handle not turning off more lighting than is necessary is to install switches where the MWBC divides into two wire circuits.

Roger

 

[don_resqcapt19]

I just came across Article 225.7 (B) which states Common Neutral is permitted for Lighting Equipment Installed Outdoors. Thank you for your help.

A "common neutral" is not the same as a grounded conductor used with multiwire branch circuits.

The "common neutral" will have more that one ungrounded conductor of the same "phase" associated with it.

The grounded conductor used with multiwire circuits can only have one ungrounded conductor from each "phase" associated with it.

 

[Smart $]

... Another way to handle not turning off more lighting than is necessary is to install switches where the MWBC divides into two wire circuits.

Roger

AFAIK, there is no requirement for the switches to be where the MWBC divides into two-wire circuits. Perhaps slightly more safe for one maintenance person working one outlet at a time on the load side of the switch, but the potential for a neutral to be or become energized still exists as long as the neutral isn't switched open.

 

[charlie b]

My proposed response is going to require installation of 2 single pole circuit breakers with identified handle tie [not a two-pole circuit breaker (in order to limit the number of lights that would turn off if maintenance needed to work on the circuit)].

There is a very particular set of circumstances through which you can start with two separate ungrounded conductors and a shared neutral (i.e., a MWBC), and then open only one breaker so as to deenergize one of the two ungrounded conductors but leave the other ungrounded conductors energized (so as to leave some of the lights on), and thereby create a shock hazard for the person working on the system. But that particular set of circumstances can indeed kill the worker. The circumstances may be rare, and creation of a shock hazard may require some inexperience or inattention on the part of the worker, but it is real, and it is the reason (or so I believe) that the NEC requires both of the ungrounded conductors to be turned off at the same time. What you are suggestion is not only a violation of code, but it also undermines the reason that that article of the code is written the way it is written.

 

[GoldDigger]

There is a very particular set of circumstances through which you can start with two separate ungrounded conductors and a shared neutral (i.e., a MWBC), and then open only one breaker so as to deenergize one of the two ungrounded conductors but leave the other ungrounded conductors energized (so as to leave some of the lights on), and thereby create a shock hazard for the person working on the system. But that particular set of circumstances can indeed kill the worker. The circumstances may be rare, and creation of a shock hazard may require some inexperience or inattention on the part of the worker, but it is real, and it is the reason (or so I believe) that the NEC requires both of the ungrounded conductors to be turned off at the same time. What you are suggestion is not only a violation of code, but it also undermines the reason that that article of the code is written the way it is written.

And to add to a previous comment, turning the light fixtures off via a switch at a point beyond which only one half of the MWBC is carried through (with a dedicated extension of the neutral) will NOT provide sufficient safety if anything compromises the shared neutral while you working on the de-energized half of the circuit. One might be safe in opening the dedicated extension of the neutral during the work, in the absence of a fault somewhere else, but I would not be comfortable with it. Especially if there is no lockout for the switch being used as a disconnect.

 

[roger]

AFAIK, there is no requirement for the switches to be where the MWBC divides into two-wire circuits.

Correct, I would put them immediately outside the panel, but that's just me.

Perhaps slightly more safe for one maintenance person working one outlet at a time on the load side of the switch, but the potential for a neutral to be or become energized still exists as long as the neutral isn't switched open.

This would be the same on any neutral down stream of the service equipment even if is part of a two wire circuit.

And to add to a previous comment, turning the light fixtures off via a switch at a point beyond which only one half of the MWBC is carried through (with a dedicated extension of the neutral) will NOT provide sufficient safety if anything compromises the shared neutral while you working on the de-energized half of the circuit. One might be safe in opening the dedicated extension of the neutral during the work, in the absence of a fault somewhere else, but I would not be comfortable with it. Especially if there is no lockout for the switch being used as a disconnect.

And as I said above, it would be no different than working on any circuit downstream of the service equipment. The service is nothing more than a MWBC itself. Think "Qualified Person" and yes, accidents can happen to the qualified too.

Roger

 

[ActionDave]

Correct, I would put them immediately outside the panel, but that's just me. This would be the same on any neutral down stream of the service equipment even if is part of a two wire circuit.





And as I said above, it would be no different than working on any circuit downstream of the service equipment. The service is nothing more than a MWBC itself. Think "Qualified Person" and yes, accidents can happen to the qualified too.

Roger

I agree. An open neutral at the start of the circuit is such a tiny hazard. I think there would be a bigger danger in being tempted to work on a circuit live instead of turning off three circuits and wiping out an entire wing of lights or every plug in the room.

 

[mwm1752]

The point of origination is the last over current device protectibg the circuit. Simple 2 pole breaker disconnecting the ungrounded conductors on a 240V 1 phase circuit sharing a neutral which is a grounded conductor. Approved breaker ties are acceptable.