engineer84
Member
How would you guys feed a 480 volt piece of equipment with say 20fla and a 30 amp main. Would you feed it with #10 and 30 amp fuses in the bus duct or would you up the fuse size and size the feed conductors accordingly?
Bus Duct Fuse Sizing
- Thread starter engineer84
- Start date
- Status
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Continuous load?
engineer84
Member
Not exactly sure of continuous load. I will have to check and see. It is minimal. I guess my question is really: Is it acceptable to over size the fuse and conductors feeding the thirty amp main and if so by how much and is that typical practice. We have seen feeds where the main and the fuses feeding are sized the same and when we have a fault condition we lose the fuse and not the breaker. This is an increased safety risk and hassle.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
I guess I'm missing the big picture. Why a breaker and a fuse?
In general 240.4(D) would dictate that your 10's are fed with a 30A breaker.
In general 240.4(D) would dictate that your 10's are fed with a 30A breaker.
Volta
Senior Member
- Location
- Columbus, Ohio
I think he means that the equipment is furnished with a CB, and will be fed from an overhead bus duct with a fused plug. Inconvenient to replace fuses, yes, but shouldn't happen often. I'd go with 30 amp TD fuses and #10, myself.
engineer84
Member
The machine is being fed from a fused bus duct switch. The 30 amp Breaker is the local main of the machine.
engineer84
Member
Volta you are correct. Is there any reason that would prevent you from upsizing the fuses if the feed conductors are sized properly as well?
Volta
Senior Member
- Location
- Columbus, Ohio
None I can think of quickly, I'd peruse Art. 430 and the industrial equip. article and industrial machinery standard first, but I think you can. But if you're talking about faults, a 60 amp fuse might still open before the 30 cb, you might want to seek some coordination info.
As long as the equipment doesn't have a nameplate (or installation instructions) that list "maximum fuse size."
You should also check that the circuit breaker has the proper AIC rating.
- Status