What size fuses

[Brownetown]

what size fuses would you use in this application. Having a debate at the moment FLA 26.7A. Largest motor 8.67. 480v

 

[infinity]

FLA 26.7A. Largest motor 8.67. 480v

What does this mean?

 

[Brownetown]

Full load amps

Control panel has 3 motors already pre wired. Existing power source was 30amp fused disconnect. I was debating thinking we need to upsize existing service but inside control panel is all wired #10awg, but 80% rule 30 amps wouldn’t cover full load. But chances are 3 motors are never running same minn ckt is 28 amps max 65 on name plate

 

[infinity]

But chances are 3 motors are never running same minn ckt is 28 amps max 65 on name plate

If the equipment gives you the MCA that's what you use to size the conductors. 28 amps, #10 minimum conductor size.

 

[Brownetown]

Right I agree if time if I used 30 amp fuses technically only good for 80 perfect would you go to 40 amp fuses?

 

[infinity]

Right I agree if time if I used 30 amp fuses technically only good for 80 perfect would you go to 40 amp fuses?

Where are you getting 80 percent?

 

[tjdilly]

Where are you getting 80 percent?

The ol 125% rule of thumb

MCA = 125% of FLA.
MOCP = 225% of largest motor plus the rest.

Breaker/Fuse sized anywhere between those two.

 

[infinity]

Right I agree if time if I used 30 amp fuses technically only good for 80 perfect would you go to 40 amp fuses?

There is no 80% in this scenario. The MCA already has calculated the minimum conductor size which would include the 125% for the largest motor. The MCA is also the minimum OCPD size but the motors may not run with only a 30 amp OCPD. You can keep the #10 conductors and use up to a 65 amp OCPD.

 

[Brownetown]

Okay that what I was wondering. I appreciate all the feedback back. Thank you

 

[Joethemechanic]

Are these something like paralleled pumps or compressor that are set up to alternate, and only run multiple pumps when demand is high?

 

[Eddie702]

If all the motors are part of the same machine you take 125% of the largest motor plus the other motor(s) amps to size the conductors. And you use the amps listed in the code not the nameplate.