PV Disconnect Grounding

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RobertCyr

Member
Location
Sycamore, Illinois
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 said:
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.
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The engineer is correct. Neutral and ground should be bonded in the disconnect and a GEC run back to the building grounding electrode system.
 
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.
 
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?
 
RobertCyr said:
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?
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Treat it just like any other service disconnect because that's what it is.
 
RobertCyr said:
... 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?
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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.
 
Yes, I agree and understand. My question was regarding the lack of GEC from disconnect to grounding electrodes, ground rods. I believe a GEC is required from the disconnect to the grounding electrodes separate from the neutral. How can the engineer be correct, according to ggunn, if he did not include a GEC there?
 
In your OP you just said 'ground', is ambiguous if you don't specify whether you mean EGC or GEC. Ggunn thought you were referring to an EGC. The engineer is correct that an EGC is not required between the meter and the disconnect. The neutral performs both the function of the neutral and EGC in that spot.

No separate EGC is needed between meter and disconnect. A separate GEC or GEC tap is needed if you choose one of those methods for grounding multiple service disconnects.
 
Think of it this way: When you have a service with 2 (or more) service disconnects, you (probably) will have one set of larger conductors that splits into 2 (or more) sets of smaller conductors. To connect the GEC, The NEC says either connect before (or at) the split, or connect GEC taps after the split. Note there is no technical reason that a GEC tap needs to be in both disconnects, its just the NEC overemphasizing the importance of the GEC connection, and they refuse to make the code actually match up with science and electrical theory.
 
electrofelon said:
Note there is no technical reason that a GEC tap needs to be in both disconnects
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I think the only justification for it is that when there is no GEC connection before the split in service conductors, then requiring GEC connections within each service disconnect provides a level of independence between the two or more systems supplied by the service disconnects. I.e. you could demo out one service completely, and not have to think "oh this is the service disconnect with the GEC, I better move it over to the other service disconnect."

Cheers, Wayne
 
wwhitney said:
I think the only justification for it is that when there is no GEC connection before the split in service conductors, then requiring GEC connections within each service disconnect provides a level of independence between the two or more systems supplied by the service disconnects. I.e. you could demo out one service completely, and not have to think "oh this is the service disconnect with the GEC, I better move it over to the other service disconnect."

Cheers, Wayne
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makes sense. At least the NEC is consistent in its irrational emphasis on the importance of the GEC connection. Having a GEC in each disconnect what take care of those types of what ifs and harmonizes nicely with the other ridiculous rules like the irreversible crimping and such.
 
electrofelon said:
makes sense. At least the NEC is consistent in its irrational emphasis on the importance of the GEC connection. Having a GEC in each disconnect what take care of those types of what ifs and harmonizes nicely with the other ridiculous rules like the irreversible crimping and such.
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Ridiculous or not I always design with neutral and ground bonded in the disco and a GEC run back to the existing grounding electrode system unless otherwise directed by the AHJ. It is simple to do and can never be wrong.
 
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