I have a 100 amp 480/277 volt service disconnect feeding a repair shop from power company transformer,service is feeding a 75 kva 480/120/208 3ph transformer bonding will be done in transformer,from transformer to a 200 amp load center, are ground bushings needed on line and load side all counduit is emt
There is no requirement to bond the conduit on the primary or the secondary of the transformer. Most electricians do it for some reason but there is nothing in the NEC that requires it. You don't need to use bonding bushings on the load side of the service disconnecting means except if there are concentric or eccentric KO's and greater than 150 volts to ground 250.97. If there is a broken ko you would need one too. That's it... Everyone seems to do it but it is not required.
Since most Rough in to Utility Transformers just come underground into an opening And PVC might be used with RSC 90's even if not. There is no Physical connect between the pipe & the ground at the transformer. The utility end would for sure require a bonding bushing. ' Comments????
At my rate of pay I am not willing to do ALL of the homework for any query.
SDS = Secondarily Derived Service
= ALL transformers ( relaxed for dinky transformers )
= ALL on site Gen-Sets
= Solar PV type power has its own NEC section -- which is not quite the same as a typical SDS... typically a dry-type three-phase transformer Delta 480 to Wye 208Y120.
The SDS rules -- and the rationale for bonding across the secondary is in 230 or 232. Use the index at the back, hint.
As for the GEC system... it's in 230 or 250...
The essence of the scheme is that bonding bushings are REQUIRED along the ENTIRE GEC bonding run.
Since there is a common habit of running the GEC of the SDS right on back to the Service -- you'll find bonding bushings used in BOTH directions primary and secondary.
This requirement is limited to STEEL/ EMT raceways, underground or above ground.
If PVC ( non-metallic raceways) is used then the need to eliminate the choking effect is gone.
So many, many Services have no bonding bushings at all: they've been run underground.
The need for bonding bushings also is missing if the GEC system is not encased in EMT/ RMC.
So, it's common for most residential installations to NEVER have a bonding bushing.
The trivial situation of a Service riser -- for an overhead residential Service is excluded from the requirement -- since it's outside the structure -- most unlikely to be touched during a surge -- and it's almost impossible to attain a voltage differential at the riser because it's going STRAIGHT UP out of reach.
If any acronym is obscure -- just post so -- and many here will post a response.