35 amp fuse in 30 amp disconnect
- Thread starter steve66
- Start date
- Status
Only if you have a big enough hammer
Depending on the specific equipment you are referencing, there is likely a minimum size allowable disconnect specified by the NEC. For instance 440.12 for HVAC and 430.110 for motors.
Once that requirement is met the rest is optional.
I do not know of a 30 amp rated disconnect that will physically accept a 35 amp fuse but there is no NEC requirement that you fuse must be equal to the max allowed.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
But there are UL listing requirements. Fuses cannot be larger than the rated size of the switch or fuse holders, however, they can be smaller.Only if you have a big enough hammer
I do not know of a 30 amp rated disconnect that will physically accept a 35 amp fuse but there is no NEC requirement that you fuse must be equal to the max allowed.
qcroanoke
Sometimes I don't know if I'm the boxer or the bag
- Location
- Roanoke, VA.
- Occupation
- Sorta retired........
"Only if you have a big enough hammer"
I believe a 35 amp fuse is physically to big to fit in the fuse holders of a 30 amp disconnect.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Yep. A 35A fuse is physically the size of a 60A one. It possibly wouldn't even fit into the enclosure, much less the fuse clips.
Only if you have a big enough hammer
That's what I pretty much assumed, but I wasn't 100% sure if a disconnect was rated based on its maximum fuse size, or it was rated based on its continuous current carrying capacity, or both.
That must be what the contractor has planned, but IMO its not the best idea. If the 30A fuses don't hold, the whole disconnect would have to be replaced.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
at least one manufacturer has a 35A class CC fuse that fits in a class CC (30A) fuse holder.
controlled
Senior Member
- Location
- Bowmanville, Canada
What manufacturer is that???
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
If you are thinking Littlefuse, who calls all of their CCMR fuses "Class CC" and says they go up to 60A, you might be mistaken. At 35-60A they are not the same size, so UL made them call them class CD. I think Littlefuse refers to them as class CC in the web page description because the current limiting capabilities are the same as the other CCMR series, but when you look at the data sheet they show a class CD for the larger ratings and they don't fit in the same fuse holder. I think it's a little misleading.
http://www.littelfuse.com/~/media/e...d-ul-fuses/littelfuse_fuse_ccmr_datasheet.pdf
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
Use 30A fuses. MOCP stands for MAXIMUM, which means you can use smaller. The 22MCA is the MINIMUM amps required, and 30A is greater. So your good. To pick the correct 30A fuse, simply coordinate the trip curve with the load and you should be fine.
- Status