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Generator feeder breaker size - brianwelch - 05-24-2022
I am looking to install a generator inlet connection and the code (and common sense) required interlock at the main circuit breaker panel. Generator is ~7,500 watt. I plan to use 8/3 romex from the 200A breaker panel to the inlet box, about 8' away. As I need to install new breakers for the generator feeders, is there a specific minimum or maximum size required? A double pole 30A sounds right, but since the breaker is really only acting as a switch, can I use one that is of higher capacity/rating?
I have researched this a bit online, and see a variety of answers...
RE: Generator feeder breaker size - brianwelch - 05-24-2022
Spoke to a local electrical contractor. He stated that since generators have circuit breakers that control load/overload, a 30amp, or larger, double pole breaker will do the trick, as it is effectively a switch, not a circuit breaker in a backfeed condition such as this.
Correction on the generator size, as if it makes a difference...6800watt continuous load, 8500watt peak/starting...
Thoughts or opinions from others in the know?
TIA
RE: Generator feeder breaker size - MstrCarpenter - 05-24-2022
I'd go with a 40 or 50 amp. Not that it really makes a difference, but are you back feeding the whole panel or adding a generator transfer switch box with only specific circuits? Either way, you do have a way to ensure you can't back feed to the pole, right?
Also, others more experienced than I are welcome to teach me, but with A.C. current I thought the breaker wouldn't know which way the power was going because, well, it goes both ways.
RE: Generator feeder breaker size - Roly - 05-25-2022
(05-24-2022, 09:59 PM)MstrCarpenter Wrote: I'd go with a 40 or 50 amp. Not that it really makes a difference, but are you back feeding the whole panel or adding a generator transfer switch box with only specific circuits? Either way, you do have a way to ensure you can't back feed to the pole, right?
Also, others more experienced than I are welcome to teach me, but with A.C. current I thought the breaker wouldn't know which way the power was going because, well, it goes both ways.
A normal breaker does not know or care which way the current is going. There are special breakers that look for reverse power but not used in a residential setting.
Also I think you will need to run 4 conductors to the gen set, neutral plus ground. Sounds like he is feeding the entire panel, so will need just turn on certain breakers to prevent over loading gen.. IF the interlock is installed correctly the gen set breaker cannot be turned on with main breaker on. Roly While I agree the larger breaker would not matter in this case, i dont think the inspector would allow it as it is also feeding a 30 amp outlet, If the interlock is removed or disabled in the future it could overload the wire and or the outlet.
RE: Generator feeder breaker size - brianwelch - 05-25-2022
Thanks all...The plan is to install an 8/3 feeder from the inlet box on the exterior of the house to the circuit breaker panel (2H, N, Gr), which will allow for a larger generator in the future, should it be necessary.
The interlock device, once installed, will prevent both the main breaker and the generator to feed the panel simultaneously (as long as the panel cover is in place).
Please let me know if there is anything I either left out, or should take into consideration.
Thanks again
RE: Generator feeder breaker size - Roly - 05-25-2022
(05-25-2022, 12:35 PM)brianwelch Wrote: Thanks all...The plan is to install an 8/3 feeder from the inlet box on the exterior of the house to the circuit breaker panel (2H, N, Gr), which will allow for a larger generator in the future, should it be necessary.
The interlock device, once installed, will prevent both the main breaker and the generator to feed the panel simultaneously (as long as the panel cover is in place).
Please let me know if there is anything I either left out, or should take into consideration.
Thanks again
Mark the breakers you should not turn on that will overload gen such as electric heat. Suggest turning off all breakers and picking up load one at a time, give a few seconds between them to allow refrigerators,freezers ac units to get past the starting currents. Also mark the breaker that controls the lighting by the panel to turn on first so you can see in the dark. Roly
RE: Generator feeder breaker size - brianwelch - 05-26-2022
Good idea on the unnecessary ct breakers...May force me to finally ID/tag all of them. Been meaning to for years...
Fortunately the draw is quite small (other than AC), due to gas appliances/heat/water heater, etc...