Disconnecting means for grounded conductor?

[JDBrown]

The issue of providing a proper disconnecting means for an outbuilding has come up a few times recently, and I find that, the more I look into the Code requirements, the less confident I am in my understanding of all the related nuances.

My latest confusion is regarding NEC 225.38(C), which says:

(C) Disconnection of Grounded Conductor. Where the building or structure disconnecting means does not disconnect the grounded conductor from the grounded conductors in the building or structure wiring, other means shall be provided for this purpose at the location of disconnecting means. A terminal or bus to which all grounded conductors can be attached by means of pressure connectors shall be permitted for this purpose.

So, a means has to be provided for disconnecting the grounded conductor (e.g. the neutral). This seemed a bit odd to me at first, because why would you want to open your neutral? This section seems to allow me to switch the neutral (say, by using a 4 pole switch on a 3 phase, 4 wire feeder or MWBC), but if I don't switch the neutral with the phase conductors I have to provide another means of disconnecting it. Based on the wording of 225.38(C), it seems that the neutral lug on a standard disconnect switch would qualify. But since it doesn't require the grounded conductor to be disconnected simultaneously with the ungrounded conductors, it also sounds like I could bring my feeder into an enclosure with two switches, one which would disconnect the ungrounded conductors and the other which would disconnect the grounded conductor.

Now, I can't think of any reason why I would want to do it that way -- to the contrary, it sounds like a very bad idea to me -- but it appears that it would be Code legal. Is this correct, or have I been staring at the NEC for so long that I'm seeing things that aren't there?

 

[iwire]

Just use a disconnecting means that is listed for use as service equipment and you are all set.

The fact such a disconnecting means has a terminal bar that the neutral can be lifted from satisfies the requirement

 

[suemarkp]

I had always assumed that a wire nut connecting the neutrals was a suitable way to disconnect it. There shouldn't be many to deal with if this is a branch circuit.

 

[JDBrown]

Yes, but why does the neutral need to be able to be disconnected in the first place? And why is the code section worded in such a way that it sounds like I could use a separate switch for the neutral, rather than switching it with the other conductors or calling the neutral lug/bus/wire nut the "disconnect"? Again, that seems to just be asking for trouble, but the Code appears to permit it. Does anybody know why? Is there some circumstance in which this would be desirable?

 

[texie]

Yes, but why does the neutral need to be able to be disconnected in the first place? And why is the code section worded in such a way that it sounds like I could use a separate switch for the neutral, rather than switching it with the other conductors or calling the neutral lug/bus/wire nut the "disconnect"? Again, that seems to just be asking for trouble, but the Code appears to permit it. Does anybody know why? Is there some circumstance in which this would be desirable?

First, we need to be sure you are talking about a feeder as opposed to a single branch circuit as the rules are different. For a feeder to an out building you use a service rated disconnect and you are good to go as iwire stated. The language for disconnecting the neutral is the same as for a service and has been in the code forever. All it means is that there is a way to disconnect the neutral by physically unhooking it-it does not mean to switch it with the ungrounded conductors. This precludes one from simply running a neutral straight through with out landing it. Also keep in mind the other requirements for an EGC and other grounding requirements when running a feeder to an outbuilding.

 

[JDBrown]

Thanks, texie. I guess it boils down to nobody's dumb enough to put a separate switch on their neutral, and no inspector is dumb enough to let them if they tried, given all the trouble an open neutral can cause. I guess I was just reading too far into it.