Hello wrenchers
We've got 2 systems [23kW and 44kW] going up on Solarmount onto a single large custom steel dunnage structure on top of a warehouse. >From the ground it will look like a single massive array, but actually 1/3 of the modules (8 strings) will be fed into (2) Fronius [which will feed one bldg service, with its own water main ground], and 2/3 of the modules (16 strings) will be fed into (4) Fronius [which will feed a different bldg service, with its own water main ground.] All of the mods will be weebed onto rails, which will be mechanically connected to the I-beams, which is welded to the building steel, which goes into the ground. We plan to land all of the DC equipment grounds onto a common bus bar near the inverter bank; from that we plan to run a bare solid #6 copper to each inverter. We'll run #6 GEC's out of each inverter, to be irreversibly crimped onto a dedicated single #4 GEC for each building, which will land on their respective water mains. The question is: does this mean we're also bonding two neutrals together, which means current could flow into the service at Building A, through a lightbulb, back to their neutral buss, up our EGC/GEC, down to Building B's neutral buss, and out through their service neutral? That may pose two issues: 1) If Building A has a 400A service and Building B has a 100A service, building B's neutral is now in major danger of an overcurrent situation. (There are probably other potential problems as well, if the two services are out of phase for example) 2) The bonded GEC now becomes a grounded current-carrying conductor This example seems pretty unique; we haven't found anything in the code yet that specifically addresses the situation, but 250.32 prohibits something similar on the grounds that it causes point #2 as above. A possible counter-argument to point #1 : does potential exist between L1/2/3 of transformer A and the neutral of transformer B? Fun stuff..cheers for reading this Jim Mac
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