Jumper cable size for wye delta arrangement

[mull982]

We have a 480V compressor that has a wye - delta starter arrangement. We have a 4/0 feed coming from a 200A breaker feeding the compressor. Inside the compressor we need to jump the line side of the main contactor to the delta contactor to complete the circuit. The delta contactor also has some auxilary motors, heaters, etc.. that come on after the main motor is started.

We need to figure out what is the minimum size cable we can use to jump the main contactor to the delta contactor. The 4/0 cable is hard to bend with such a small radius so contractor wants to use smaller cable. I am arguing that cable piece will need to be at least 200A capacity since this is what the feeder breaker upstream is. Although the main motor has an overload device inside the delta, this overload device is only providing overcurrent protection to to the motor windings, and not necessarily to the feeder cables to the compressor since as I mentioned the delta contactor has other auxilary loads on it. The main motor leads are 1/0 and the contractor is saying that the jumper cable can be 1/0 as well. I am saying that it needs to be at least capable of 200A (At least 3/0) since there other auxilary loads on the delta contactor that the main motor overload does not look at and therefore protection will be left to the upstream breaker.

Do you guys agree with me?

 

[Cold Fusion]

... The 4/0 cable is hard to bend with such a small radius so contractor wants to use smaller cable. ...

...I am arguing that cable piece will need to be at least 200A capacity since this is what the feeder breaker upstream is. ...

...The main motor leads are 1/0 and the contractor is saying that the jumper cable can be 1/0 as well. ...

Do you guys agree with me?

The main motor leads are likely high temp wire and can be small and still handle the current.

If you want 200A - tell him, "200A".

However, stay away from THHN or XHHW. Consider DLO or other fine strand cable. That's pretty common inside of cabinets - and a lot easier to bent short radius.

cf

 

[Jraef]

I'm a little concerned that you are feeding "other loads" off of that same breaker. Technically, ALL of that other wiring would need to be rated 200A. You can get away with smaller conductors if the motor were the ONLY load, but as soon as you added that other stuff, that 200A breaker became a branch circuit breaker, not a motor circuit breaker, so all the special rules pertaining to single Motor Circuits went out the window.

 

[don_resqcapt19]

...
However, stay away from THHN or XHHW. Consider DLO or other fine strand cable. That's pretty common inside of cabinets - and a lot easier to bent short radius.

cf

I like the fine stranded wire for the reason you stated, but the installer has to make sure that the terminations are rated for use with that wire. Standard terminations, especially of the set screw type, may not be suitable.