continuous duty

Merry Christmas
Status
Not open for further replies.
B

buck33k

Senior Member
Location
Washington state and North Carolina
I have a 3 phase 208 Volt 20hp air compressor.

Name plate FLA 60 amps.
430.250 FLA 59.4 amps

It is replacing a smaller 3 phase compressor supplied by #6thhn.

The note below table 430.22(E) reads: "Any motor application shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not operate continuously with load under any condition of use."
I'd say this motor will will not operate continuously under any condition of use.

Can the existing circuit be used with this compressor considering the note quoted, or must it be upsized to #4?
 
The minute rating is how the manufacture rates the motor not the application it is used in that is the duty cycle
 
Branch circuit conductors

Branch circuit conductors

I have always been under the assumtion that the branch circuit conductors must be rated at 1.25% of the FLA taken from the table in section 430. Intermittent usage I don't think that will stand in this case. I have seen air compressors running for hours at a time in woodworking shops.
 
I went out today and wired the motor/compressor (duty continuous). Used #4 cu in one inch conduit.

My thinking now is that it would be very rare to not size the motor circuit conductors at 125%, and table 430.22(E) affords no reduction to common installations. I ca'nt say I've actually seen a 5, 15, 30, or 60 min duty cycle motor, maybe they're common. And, as Bea indicated, the minute rating is how the manufacturer rates the motor and not the application it is used in.

Whats interesting to me is that if I'm using a continuous rated motor in a short time, intermittent. or periodic application, 125% FLA motor circuit conductors would'nt be sufficient, or so it would seem.
 
If this is a Industrial setting I would treat it at continuous duty. I have been in plants where the compressor runs most of the time. Air leaks everywhere, and machines using compressed air to operate. Size at 125%. I do not think art.430.22 (E) applies in this application.
If you read further in this article you will see that AHJ may grant this permission.
So 430.22 applies if permission not granted.
 
Status
Not open for further replies.
Top