I was asked to relocate an existing 75 HP air compressor. The nameplate info on the compressor control panel label stated: FLA 96 amps @ 480V 3ph. 3W. I've always sized the conductors feeding a piece of equipment at 125% of the stated FLA. To my surprise the previous installer had fed the compressor with #3 THHN cu, 100 amp rated wire, not the #1 THHN cu which covered the derating factor of 120 amps. Simple question, but I've run into disagreement about what the equipment nameplate includes/ doesn't from manufacturers and inspectors alike. I'd like to get this cleared up if possible.
Conductor sizing/equipment nameplate rating
- Thread starter kerajam
- Start date
- Status
In my opinion;
96 amperes is 96 amperes period. Motor device conductors must be sized as a continious load @ 125% capacity. There is not much more to say about it. The previous installer goofed, you did not.
Did you also take into consideration ambient temperature, distance and voltage drop in your conductor sizing?
96 amperes is 96 amperes period. Motor device conductors must be sized as a continious load @ 125% capacity. There is not much more to say about it. The previous installer goofed, you did not.
Did you also take into consideration ambient temperature, distance and voltage drop in your conductor sizing?
- Location
- Massachusetts
If the FLA is taken from a tag off of the combined equipment the 125% should already be factored in.
If the info was taken from the motor itself you would add 125% to the value found in the tables of 430.
If the info was taken from the motor itself you would add 125% to the value found in the tables of 430.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
iwire said:
I am assuming you are referencing 430.7(D)(1)?
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