Grounding Supply-Side Connections on PV Systems

E

EWEngineer

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Location
California, USA
Occupation
Director of Engineering
Greetings All,

I have a question that has been unclear to me for several years and I have found no conclusive explanation or justification. When designing a PV system with a supply-side connection (Line side tap), a service disconnect is installed. What has been done in the past is to install a GEC from the ground bar in the disconnect back to the existing grounding electrode system. It seems to me that this scenario is most accurately described by a supply side bonding jumper from the main switchboard, where the current GEC is installed, to the new service disconnect (See NEC Exhibit 250.12).

Can anyone please provide clarity?
 
EWEngineer said:
...
Can anyone please provide clarity?
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No. 😁

Seriously, this has been something that has been unclear and apparently something of a bone of contention between code making panels over the years.

The sensible way to treat it would be as a separate service disconnect and for the GEC you then follow 250.64(D). That section says you should run a separate GEC or GEC tap to the electrode system or main GEC, (implying outside of any raceway containing the circuit conductors), unless your existing GEC connection is upstream of the supply side tap (in which case no new GEC might be necessary). That said, there have been proposals to clarify grounding in 705.11 but they have never made it into the code. (Bonding got a mention, but not grounding.) So that may leave open the idea of an SSBJ like you suggest.

Your AHJ may have a particular opinion.
 
I think under the 2023 NEC it is pretty clear you should treat it as any other service disconnect, where it invokes article 250 parts II through V. Previous codes do not call this out.
 
Thanks for the reply. I have a follow up question. Suppose you have a utility meter between the service disconnect and main switchboard. What would be used to bond that meter enclosure?
 
EWEngineer said:
Thanks for the reply. I have a follow up question. Suppose you have a utility meter between the service disconnect and main switchboard. What would be used to bond that meter enclosure?
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An EGC, although I think there's an exception that allows it to be the grounded conductor (neutral) for meters. One of the very few cases where the NEC cares about equipment being a meter.
 
I believe if the meter is before the main service disconnect, it may be bonded using the neutral. If it's after, then a dedicated EGC is needed to bond to the enclosure.
 
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