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While doing work in my breaker panels I noticed the following:

300A service enters into a large box on the right where it is split to a 200A and a 100A panel. Neutral and ground are bonded in the splitter box (d) AND in each of the main panels. The boxes are joined by conduit (c) and there is also a wire joining the combination neutral/ground bus in each of the two load centers to the splitter box (a). The splitter box is also connected to the cold water (b) and to a ground rod outside.

From the limited understanding I've developed of how grounding should work, it seems to me I have neutral and ground bonded in multiple locations here. Is that ok? This was all done by a licensed electrician.

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You have two service disconnects, so this is mostly fine

Your situation where you have a splitter box or trough as part of the service hardware is not at all unheard-of. Since the two panels each have their own service disconnect, they have their own bonding means to go with it. This isn't much different from a duplex with two meters/panels fed from a single service entrance via a similar splitter box/trough, and likewise, that trough needs to be bonded to the service neutral, just like a meter pan. This is also a legal place for the grounding electrode conductor connection to be made, as NEC 250.24(A)(1) permits that connection to be made anywhere from the load end of the service drop/lateral to the neutral bus on the service disconnecting means.

However, there is one issue, and that's the excess of bonding jumpering going on here, as that effectively parallels the neutral going from the meter out to the panels. Utility and local Code standards permitting, I would have the rigid nipples between the splitter box and panels replaced with PVC, or at least fitted with insulating couplings, so that service neutral current can't stray onto parallel bonding paths, and the extraneous bonding wires from the trough to the panels removed. This corrects a NEC 250.6(A) violation due to the parallel paths and also eliminates the need for bonding bushings + their associated jumpers.

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  • The conduit from the splitter box to the meter, not shown in the picture, is PVC. The only parallel paths are the ones I've illustrated, ie the "c" conduits and "a" ground jumpers. I'm not sure if, or how much, that alleviates your concern about parallel neutral current. Note, I think it goes without saying, but in addition to the two paths shown (pipe and jumpers) there is also an appropriate neutral conductor inside each pipe. – jay613 Feb 6 at 3:13
  • @jay613 -- well, that's one potential problem down – ThreePhaseEel Feb 6 at 3:16

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