250 amp cord drops

[teco]

Hello
Only my 2nd post so here goes. I need to supply a new tool with three cord drops and it needs 480 volts 250 amps three phase 4-wire each drop. The connected load is aprox 200 amps each. They want me to use 3/0 - 5-wire cord type PPE they already own from wiring other tools with smaller loads. The problem is most of the three phase load is power supplies and drives and the like and I believe up to 70% is nonlinear load. There is also a panel built in which also uses the neurtal. Even with 4/0 after derating I come out with about 221 amps. Any input would help.

Thanks.

 

[teco]

Sorry
The voltage is 208 not 480
Thanks

 

[winnie]

I presume that on the basis of the non-linear loading you are counting the neutral as a current carrying conductor and thus derating.

Keep in mind that "line-line" non-linear loads do not put harmonic loading on the neutral. A drive with a 3 phase rectifier input will not have any direct influence on the neutral. Additionally, if the power supplies have 'power factor correcting' input stages, then they will not put significant harmonic loading on the neutral.

You are correct that if there is significant harmonic loading of the neutral it should be counted as a current carrying conductor, and the presence of non-linear loads indicates that you should examine this more closely.

-Jon

 

[teco]

Thanks for your input. I am trying to get more info on the equipment.

 

[kingpb]

Based on the information at hand, I'm not sure what input you are looking for or what can be offerred, other then what Winnie has already provided.

Perhaps provide a more straigthforward question or addtional detail would be helpful.

 

[teco]

My question is can I use the 3/0 cord the in house electrician wants me to ?
Thanks

 

[kingpb]

#3/0 AWG type PPE 5-conductor cable is rated for 210A, therefore I do not see how you can legitimately put it on a 250A breaker. Max breaker size would be 225A. Which means you cannot load the cable to more then 180A. With 200A connected, what is the calculated running load? If equal to or less than 180A then your OK from that standpoint assuming you don't need to up size for voltage drop. As far as 200% neutral, I think that is something you will need to field check. If possible do a hook-up on one machine and then do some metering to see if you have an inbalance causing stress on the neutral.

 

[teco]

Good advice.
Thanks.

 

[frenchelectrican]

let me add one wise advise as well use the TSR clamp ampmeter becasue you will intercounter with the electronic system it will wreck hovac with standard ampmeter.

Merci, Marc