Confused when the genset output breaker is sized larger or smaller then the normal feeder and panel served (these are examples). I'm thinking if the genset output breaker is smaller (say 100A cb with a 200A normal system and 200A main breaker N/E panel), keep the feeder to the genset the same size as the normal source. All would be rated for 200A except the genset output breaker. However, if the normal feeder is rated for 100A and the panel served has a 100A breaker, but the genset output breaker is 200A, does the genset feeder get sized to 200A up to the transfer switch or also from transfer switch to the panel? Or does the system need to be upgraded to all be 200A rated? What NEC articles would be applicable to determine and this all is after the generator output breaker on the genset.
genset feeder and normal feeder
- Thread starter mjmike
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Tap rules?
Generator breaker smaller is the easy one..size the conductors based on the generator breaker...
Generator breaker larger would get stickey.. as Larry states, the conductors would have to be sized full size based on the generator UNLESS you can apply tap rules but the specific rule could pose problems as there are requirements to terminate on
an overcurrenr device with some tap rules so terminating on a ATS would not fit the bill.
Generator breaker larger would get stickey.. as Larry states, the conductors would have to be sized full size based on the generator UNLESS you can apply tap rules but the specific rule could pose problems as there are requirements to terminate on
an overcurrenr device with some tap rules so terminating on a ATS would not fit the bill.
I agree with the smaller genset. Looking at 240.2 definition of tap conductors and exhibit 240.2, if the conductors are protected at or below their ampacity, they are not taps. So, in the case where the genset output breaker is smaller, then the genset feeder up to the ATS just needs to be sized to the genset breaker.
Would I be correct in saying in the case of the larger genset, to avoid taps rules, the genset feeder, feeder to the N/E panel and the panel main breaker all have to get upgraded to the genset breaker size? The normal feeder could remain its original size.
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