PV Disconnect Grounding

[RobertCyr]

I have a PV roof mount system using a supply side connection at the meter, Milbank. The conduit to the PV disconnect is not calling for a separate ground. The plans essentially call for the neutral to be the neutral and ground. I can not find a code to support this but engineer claims this is standard. I have never seen this "dual" function for the neutral before.

 

[RobertCyr]

 

[ggunn]

I have a PV roof mount system using a supply side connection at the meter, Milbank. The conduit to the PV disconnect is not calling for a separate ground. The plans essentially call for the neutral to be the neutral and ground. I can not find a code to support this but engineer claims this is standard. I have never seen this "dual" function for the neutral before.

The engineer is correct. Neutral and ground should be bonded in the disconnect and a GEC run back to the building grounding electrode system.

 

[jaggedben]

The one thing missing from the diagram - which ggunn already mentioned - is that the PV disconnect should arguably have a GEC to the grounding electrodes just like the 'regular' service disconnect for the loads. See 250.64(D) option for multiple GECs or GEC taps. Alternatively, the single GEC shown could be connected to the neutral in the meter enclosure per the NEC, although often this is frown upon by utilities or because when the utility tags out the meter it becomes inaccessible. (If there's a trough between the meters and disconnects that's another possible place to do it.)

Note: the situation here is the same as any service with two service disconnecting means. The dual function of the grounded conductor on the line side of the service disconnect is true for every grounded service. You've seen it at every service you've looked at, you just haven't understood.

 

[RobertCyr]

9I think I am understanding. I questioned the lack of GEC to the grounding electrodes. How can the engineer be correct if you both think there should also be a GEC to the grounding electrodes? Any service with 2 disconnecting means would also be "grounded" together or in the same cabinet. This system has a PV disconnect remotely located from the service meter that is only grounded through the neutral. I am trying to understand an installation that I have not seen before. The question is, should there be a separate GEC from the PV disconnect to the meter, or service? Or is it code compliant to use the neutral (grounded conductor) as a "neutral" and "ground" to the PV system?

 

[ggunn]

9I think I am understanding. I questioned the lack of GEC to the grounding electrodes. How can the engineer be correct if you both think there should also be a GEC to the grounding electrodes? Any service with 2 disconnecting means would also be "grounded" together or in the same cabinet. This system has a PV disconnect remotely located from the service meter that is only grounded through the neutral. I am trying to understand an installation that I have not seen before. The question is, should there be a separate GEC from the PV disconnect to the meter, or service? Or is it code compliant to use the neutral (grounded conductor) as a "neutral" and "ground" to the PV system?

Treat it just like any other service disconnect because that's what it is.

 

[jaggedben]

... The question is, should there be a separate GEC from the PV disconnect to the meter, or service? Or is it code compliant to use the neutral (grounded conductor) as a "neutral" and "ground" to the PV system?

Don't conflate two different things.

The neutral provides the effective ground fault return path to the utility transformer. It must be brought to each service disconnect and bonded (see 250.24(C)).

The GEC provides a connection to earth. Again, the NEC provides multiple options for how to install the grounding electrode conductor(s) when there are multiple service disconnects. See 250.64(D) for the details.

These two things provide different functions.