Air Compressor Load

[CCCI]

Would check my numbers? I have a 10HP air compressor (208v ? 3phase) that I need to hook-up.
It is 10HP
208 3phase
Service Factor 1.15

My calculated load is:

10HP 30.8 Amps
60 Amp Fusible Disc.
60 Amp Time Delay Fuse
80 Amp Circuit Breaker
3#8 THHN/THWN & 1#10 GRD. In 3/4? Conduit

Can I go lower on the Fuse and/or the breaker for the feed?

 

[LarryFine]

Can I go lower on the Fuse and/or the breaker for the feed?

You can go as low as will still allow the motor to start.

 

[barbeer]

I would go with a no-fuse dico, you are already protected @ the breaker!

 

[bob]

Would check my numbers? I have a 10HP air compressor (208v ? 3phase) that I need to hook-up.
It is 10HP
208 3phase
Service Factor 1.15

My calculated load is:

10HP 30.8 Amps
60 Amp Fusible Disc.
60 Amp Time Delay Fuse
80 Amp Circuit Breaker
3#8 THHN/THWN & 1#10 GRD. In 3/4? Conduit

Can I go lower on the Fuse and/or the breaker for the feed?

Bussmann suggests a 40 amp TD fuse for this size motor. As Barbeer noted,
you do not need the 80 amp breaker and the time delay fuse.

 

[augie47]

CCCI: A suggestion::: You might double-check the nameplate on the compressor motor to see if it is a "true" 10 HP motor. Being 3 phase, it probably is, but the aircompressor folks "play games" with the "ratings" on compressors and the advertised compressor horsepower rating doesn't always match the actual motor HP.

 

[CCCI]

CCCI: A suggestion::: You might double-check the nameplate on the compressor motor to see if it is a "true" 10 HP motor. Being 3 phase, it probably is, but the aircompressor folks "play games" with the "ratings" on compressors and the advertised compressor horsepower rating doesn't always match the actual motor HP.

Yes the 10 HP comes from the nameplate on the motor.

 

[mayanees]

Application of unfused disconnects

Application of unfused disconnects

Beware the use of an unfused disconnect in the event that there is more than 10,000 amp short-circuit availability.

My experience has been that if the available fault current exceeds 10,000 amps, then the upstream OCPD must be a rated/listed combination, which is to say that you can't protect a Square D unfused disconnect with Siemens breakers.

And my experience has been that unfused disconnects have a 10,000 amp withstand capability.

I did a project for an industrial facility where they ignored the requirement for fused disconnects, then submitted the unfused ones for approval. Out of 85 disconnects, only about 15 had to be replaced with fused disconnects, which then carry the rating of the fuses.

JM