So here's the situation: I have 5 generators paralleled to a paralleling switchgear. The generators are installed outdoors and the switchgear is indoors. The installer grounded the neutral of each generator and also grounded the neutral of the paralleling gear. When I discussed this with the installer, I told him that he needs to break the ground connection at either the generators or paralleling gear so that both are not grounded at the same time. His reply was that the generators, being outdoors are similar to a transformer being installed outdoors which, per NEC 250.24(A)(2) would require grounding at both the source and service panel. Does anyone have an opinion or code reference for this argument either way? ..
Asumption: The system is grounded 480Y (seems reasonable from some of the comments) But if 208Y, my response still stands. if 13.8KV, well, solidly grounding 13.8 is pretty nuts.
Yes I have an opinion. I deal with this alot - multiple, paralleled, generators, both on-grid and off-grid.
The code, bless their souls, just don't deal with this. Their one rule covers all - does not fit. This is not a cookie cutter installation. If you looking for a code reference that you can stamp on the drawing and say "make it like this.", you're beat.
The idea of bonding multiple paralleled gens at the sources is a really bad design choice - ground grid or not - OCP at the gen or not - outside or not. This is not something that can be designed using a code section. One must actually apply engineering. Any decent solution will be far past the safety, reliability, and performance mandated by code.
Just curious, how come you are dealing with the installer? I've never seen a multiple gen project that did not have engineered drawings. Isn't there an engineering group that is "engineer of record" - the ones that came up with the design and drawings? I would think these are the ones that should be defending the installation.
I can tell you this about bonding each gen neutral to the equipment grounding conductor at each gen:
1. Consider most multiple gen sites are industrial, and have ground grids, metalic piping connections, and probably equipment grounding between all of the structures. Any neutral current will eventually find it's way back to a generator neutral - and some of it might even travel down a neutral conductor.
2. This sounds like small generation (each <800KW - probably < 500KW) One issue often assocoated with paralleled, small generators is if one gen winding faults, the others (in parallel) can deliver sufficient fault current that the faulted gen disappears into flying molten slag. Yes, this is with the gen mains set up correctly.
Generally speaking, it's a really good idea to arrange the N-G bond to limit the maximum ground fault current and keep the neutral current on the neutral conductors. Regardless of the code, N-G bonds at each gen won't do that.
ice