Neutral to ground bond when neutral is not used?

[ggunn]

I have a vague memory of this being discussed before, but I can't remember the details, nor can I find the discussion, so please bear with me.

Say I have a three phase inverter that does not require a neutral which is to be connected to the supply side of a service disconnect. Is there any reason to bring the neutral out to the fused AC disconnect and bond it to ground other than to bond neutral to the enclosure? It would be bonded to ground at that point, anyway, so the enclosure is bonded to ground through the GEC, and neutral is bonded to ground in the MDP or service disco, so voltage on the CCCs is already referenced to ground.

What would be the point of bringing neutral out to the disco? I seem to remember someone saying that it should be done, but I cannot remember why.

 

[wwhitney]

Say I have a three phase inverter that does not require a neutral which is to be connected to the supply side of a service disconnect. Is there any reason to bring the neutral out to the fused AC disconnect and bond it to ground other than to bond neutral to the enclosure? It would be bonded to ground at that point, anyway,

What ground would it be bonded to?

If you only brought 3 ungrounded conductors to the AC disconnect, then there would be no ground or neutral to bond the disconnect case to.

Under prior to 2020 NEC, you could plausibly instead grab an EGC from the other service disconnect and use it. That would provide a fault clearing path.

Under the 2023 NEC, it is to be treated like any other service. So you bring the neutral service conductor to it, bond the disconnect case to the neutral, install a main bonding jumper, and then that starts your new EGC system that runs with your solar feeder conductors.

Cheers, Wayne

 

[electrofelon]

For a service disconnect, we are required to bring the grounded conductor (aka neutral) to the disconnect, even if not used, to serve as the bonding conductor back to the source. For separately derived systems, and medium voltage systems, we can use a supply side bonding jumper. I am not exactly sure why the difference, although of course it's kind of semantics and just the color and name of the conductor. Due to the long-standing ( until recently ) vagueness of the grounding and bonding details of supply side connections, my first thought without diving into the languages that either would be allowed. I don't think you could rely on a gec even though it would connect back to the source due to 300.3 B.

 

[jaggedben]

. Is there any reason to bring the neutral out to the fused AC disconnect and bond it to ground other than to bond neutral to the enclosure?

There's no other reason, but that's reason enough. The neutral (really the grounded conductor, as electrofelon said) is the main ground fault current return path on the supply side of the service disconnect. In a grounded system, that's as equally important a function as it's use as a circuit conductor.

See 250.24(C). In the 2020 code 250.25 clarified that this is how they want it done for supply side connections. Of course, it does not really matter if the ground fault current path is taped green or white, but perhaps there's something to be said for consistency, and (in most cases) a slightly shorter ground fault return current path.

It would be bonded to ground at that point, anyway, so the enclosure is bonded to ground through the GEC, and neutral is bonded to ground in the MDP or service disco, so voltage on the CCCs is already referenced to ground.

Leave the GEC out of it as that could be a really roundabout ground fault current path and also more likely to get damaged or disconnected.

What would be the point of bringing neutral out to the disco? I seem to remember someone saying that it should be done, but I cannot remember why.

At this point, 250.25 is the reason not to use an SSBJ instead.

 

[ggunn]

Please pardon my density, but when I bring the supply side CCCs out to a fused disco when I need the neutral on the load side of the disco for (for example) an eGauge monitoring system, I bring a neutral out to the disco, bond it to the enclosure and to ground, and run a GEC sized to 250.66 from the disco back to building ground. I have done this many times and it has always been accepted by the AHJ. Is there something wrong with that?

 

[jaggedben]

No.

 

[ggunn]

No.

Whew!

OK, then. If I do not need the neutral, bringing it out to the disco seems redundant to me.

 

[jaggedben]

That's not what you just asked.

Per 250.25 the neutral is always necessary now. You should be considering any green/bare wire run with the CCCs as the redundant wire now, not the neutral.

The GEC may or may not be necessary and/or redundant at that location depending on where the existing service GEC is located.

 

[ggunn]

That's not what you just asked.

I realize that, but it was my original question.

Per 250.25 the neutral is always necessary now.

Are you referring to 250.24(C) to which 250.25 (A) points?? I see that, thanks.