overcurrent protection

[steveng]

i have a 10hp duplex recip air compressor used for control air of pneumatic controls, the fla is 13.6a @ 460 3ph



it is fused at 60a now, is this based on the inrush of both motors starting during initial start?

since there is an alternator and only 1 compressor runs at a time after
the initial start up. the pressure switches open at 90psi.

or could you fuse this lower, say 30a?

any suggestions?

 

[DavidA]

I'm not sure on this one as any example that I've seen in the classes I've taken were based on single motor loads. It seems like 45A single element fuses might work for short circuit/ground fault (430.52) but I'm not sure how the calculations change for multiple motors on a branch circuit.

 

[benaround]

i have a 10hp duplex recip air compressor used for control air of pneumatic controls, the fla is 13.6a @ 460 3ph



it is fused at 60a now, is this based on the inrush of both motors starting during initial start?

since there is an alternator and only 1 compressor runs at a time after
the initial start up. the pressure switches open at 90psi.

or could you fuse this lower, say 30a?

any suggestions?

steve, Don't forget that when the motor starts it has 90lb's head pressure to

overcome. Motors draw 6x, 8x, even more when starting 13.6 x 8= 108.8amps

Depending on the type of fuse 60a is right on the line, but IMO, is ok

 

[steveng]

thanks

thanks

steve, Don't forget that when the motor starts it has 90lb's head pressure to

overcome. Motors draw 6x, 8x, even more when starting 13.6 x 8= 108.8amps

Depending on the type of fuse 60a is right on the line, but IMO, is ok

thanks frank, david , i appreciate your responses.