PE (Electrical), NABCEP certified
- Austin, TX, USA
- Electrical Engineer - Photovoltaic Systems
Setting the NEC aside for just a moment... What electrical difference does it make if the ground and neutral are bonded in the PV system AC disco or not when they are bonded a few feet away in the MDP and there are no switches, breaks, or splices in either conductor between the two points? I know of at least 12 systems 150 to 400kW designed and installed the way I describe which were vetted by three different AHJ's and passed all electrical and PV inspections. Something I have not mentioned before, if it makes any difference, is that there also are supplemental ground rods in these systems at the inverters which are tied to the MDP GEC through another conductor.I think I'm going to have to eat my words from my last post. I don't think what you are proposing is compliant.
First of all, the EGC you mention from the PV disco. through the tap box to the MDP ground bar does not comply. This would be akin to having 2 service disconnects while only one has the neutral bonded and the second disco does not have the neutral bonded but instead has an EGC run to the first disco. In your scenario, if there was a short to the enclosure of the PV disco of the conductor(s) from the supply side tap, the fault current supplied from the service would flow over an EGC to get to the service neutral in another panel.
250.24(C) requires neutral bonding at EACH disconnect that is connected to service conductors. In addition, unless the GES system is connected at a common point ahead of the original disconnect, the PV disconnect would also have to have a GEC from it to the GES.
Beyond what we have discussed here, bonding in both places would put current on the ECG between the two points if there were any on the neutral, which is, I thought, what we are not supposed to do. Are you saying that the ECG from the inverter should terminate in the disco and not be carried back to the MDP?
EDIT: If anything I have written comes across as combative, I do not mean it to be. I have a vested interest in designing the safest and most compliant systems possible. Grounding sometimes resembles gris gris (Cajun black magic) to me; maybe I should bring a dead cat and some burnt chicken bones to inspections.