Supply-side vs Load-side PV Interconnection

[ggunn]

I realize you are aware of that for your particular installation. What I'm saying is the Code is written from the perspective of not knowing. What if the main bonding jumper at the service disconnect, sized to its tap conductors, is smaller than your [so-called] EGC?

It's never going to happen. We are limited to the size of the service with a supply side interconnected PV system.

Still reading the rest of your response...

 

[Smart $]

If the inverter requires a neutral, then I don't see why you wouldn't run a neutral to the disconnect and bond it there. It's the same as what would be done for all other service disconnects of any kind. The fact that it is PV really shouldn't change things because we are concerned with the available fault current from the utility, and the size and direction of the energy flow in normal operation is really irrelevant. The fact that some AHJ's don't seem to get this point (or don't care!) is disturbing, regardless of how they decide to enforce an effective ground fault pathway.

Yep.

If the inverter doesn't require a neutral, then perhaps the issue is a little stickier, since particularly on larger systems it could be an unnecessary burden to run two conductors (neutral and GEC) when only one (combined PV GEC/EGC) might be a sufficient ground fault path. Probably the one conductor is sufficient, but I'd say it ought to be terminated in the same enclosure where the tap is made. And this only makes sense if the GEC and EGC requirements both have the same destination. That is, if the GEC is going straight to the electrode from the disco, rather than passing by the tap, then you might as well call the conductor going to the tap a neutral, for consistency's sake.

Well here's an argument that'll perhaps sway some believers that the PV System disconnect is not a service disconnecting means. If it is, 250.24(C) requires the grounded conductor to be brought to each service disconnecting means. So the only way you cannot bring a 'neutral' to the PV System disconnect is if it is not a service disconnecting means. Otherwise, refer to your preceding paragraph...

Whether you tape it white or green, whichever conductor is providing the the effective ground fault pathway back to the utility needs to be bonded to the disco and should be sized to 250.66 not 250.122 (however small in consequence that may be).

The effective ground fault current pathway should always be the grounded conductor on the service side... and thus white.

 

[Smart $]

It's never going to happen. We are limited to the size of the service with a supply side interconnected PV system.

Typically yes... but we also have to be concerned with the atypical... because we just don't know.

Let's say you have a service that's established as 200A because you have a 200A solar farm in the backyard, but your house load is only 100A. You tap in for each at the meter and your SEC to the PV System disconnect are sized for 200A... but your SEC taps to the house is only sized for 100A. The main bonding jumper for the house service disconnect is sized based on the 100A SEC, not the 200A SEC prior to the meter or the SEC to the PV System disconnect.

 

[ggunn]

If it does nothing else, this discussion supports my point that this should be expressly and explicitly addressed in 690 and/or 705. If it's this controversial (and it is), the code writers should make the call and publish it so that we all do it (and inspect it) the same way. Supply side interconnection for PV is becoming very common.

 

[ggunn]

OK, so I accept that bonding the inverter neutral to the EGC in the disco and running a GEC from the disco to ground instead of continuing the ECG back to the service may be the best practice, but what if there is no inverter neutral?

 

[Smart $]

OK, so I accept that bonding the inverter neutral to the EGC in the disco and running a GEC from the disco to ground instead of continuing the ECG back to the service may be the best practice, but what if there is no inverter neutral?

Well here's where one has to decide whether it's a service disconnecting means or not.

If it is, then a grounded conductor is required on the POCO side, if POCO is a grounded system. Everything, other than not running a neutral on the PV side, is the same.

If POCO is an ungrounded system, there is no main bonding jumper. Grounding will be the same, plus a ground detector will be required.

If POCO is a grounded system and this is not a service disconnecting means, then everything is the same as the immediately preceding paragraph except a ground detector would not be required.

Essentially, the grounding system on both sides will always be the same regardless of configuration on either side. The only part that would change is whether there'll be a grounded-to-grounding bonding jumper or not (or a ground detector will be required in the case of an ungrounded system).