Just wondering how grounding, bonding and separation of ground and neutral apply to a situation like this: A 200 AMP service meter box is attached to the metal siding of a pole barn using unistrut channels and the neutral in the meter box is bonded to the meter box which in turn bonds it to the metal siding via the unistrut channel. The main 200 amp panel has the Ground and Neutral buses bonded and the grounding electrode conductor originates here and terminates in two grounding electrodes. Does the neutral from the service being bonded to the metal pole barn siding pose a potential problem?
I am going to say this is a problem and it is not a code violation yet or maybe it is if you can demonstrate the siding is in parallel to the neutral and carries objectionable current.
In Saskatchewan, I know a couple of fires are attributed to such an arrangement.
Service is at 1 end of a metal sided building where the Utility neutral is used to bond the meter base. the neutral lug is directly attached to the meter box. at the other end of the building the service is grounded with a bonding jumper installed. the raceway between is parallel with the neutral. while this is and has been code compliant for decades it is just plain wrong. maybe when the raceway is only a nipple from the meter base to the service panel and only 6 inches long that it is not dangerous the problem in Saskatchewan is related to damage to the raceway where the pipe is separated and possible stress to the neutral also opens that conductor then the metal skin takes on current carrying duty and the thin metal skin is hardly made for neutral currents.
If adopted for the 2018 Canadian code, this practice will finally eliminate using the neutral to bond meter bases or to address the parallel neutral in another way. IE if the service raceways were PVC this would still be a problem when mounted on metal siding or even stucco wire could create a parallel path.
Some of the issues or possible solutions might include an isolated neutral in the meter base and a bonding wire added between the meter base and service box. Ground at the meter base and remove the bond jumper in the service panel. Might not be allowed unless the meter base is also approved as a service box. It is not in Canada but you are in the USA so there will be variations in product approvals.
We have so many rules to prevent the neutral from being bonded or grounded more than once but we still have at least 1 rule that expressly allows the neutral to be bonded twice.