Phase Converters

[txsparky]

I am trying to size the conductors for a phase converter for a 25hp 230v 3ph. motor from a 230v single phase service. I'm trying to make some sense out of what 455.6(A)(2) is trying to say....

(2) Fixed Loads. Where the phase converter supplies specific fixed loads, and the conductor ampacity is less than 125 percent of the phase converter nameplate single-phase input full-load amperes, the conductors shall have an ampacity not less than 250 percent of the sum of the full-load, 3-phase current rating of the motors and other loads served where the input and output voltages of the of the phase converter are identical.

Could someone please translate this for me?

 

[iwire]

Re: Phase Converters

I will take a shot at it, but you better wait till some others chim in.

If you run conductors sized at 125% of the phase converter rating you are all set.

Or you can run conductors sized less than the rating of the phase converter but the conductors will need to be at least 250% of the fixed load served.

If your phase converter is rated much higher than the load served it might be cheaper to run conductors rated at 250% of the load served rather than conductors based on 125% of the converter rating.

In your case if the phase converter is rated 200 amps or more it would be cheaper to go the 250% route to sizing your conductors.

125% of 200 amps would need 250 kcmil conductors but 250% of your motor would need 2/0 copper. (25HP 3 phase 230 volt 68 amp with conductors rated 250% of that for 170 amps)

The only time I would think the 250% way would be an advantage is if you are feeding multiple fixed loads from one large converter.

Hope I got it right.

Bob

[ August 05, 2003, 05:15 AM: Message edited by: iwire ]

 

[don_resqcapt19]

Re: Phase Converters

Bob,
I think that you have it almost correct. The conductors in question are the single phase feed to the converter. This permits you to size the converter feed to the actual load and not to the converter itself in cases where the converter is oversized for the motor load.
Don

 

[txsparky]

Re: Phase Converters

Bob, Don,
Thanks alot! My mind was drawing a blank. I think I got it now. :roll:

Donnie