Quick Help on number of wires
Quick Help on number of wires
(OP)
Hello
We have a 350 HP pump running on 3 phase 440 Volts wire. Each phase has 2 wires in it.
Question is why are these 2 wires required generally (I can provide the rating if necessary)? Is that for load or redundancy? Is it possible to remove one wire and operate on single wire?
We have a 350 HP pump running on 3 phase 440 Volts wire. Each phase has 2 wires in it.
Question is why are these 2 wires required generally (I can provide the rating if necessary)? Is that for load or redundancy? Is it possible to remove one wire and operate on single wire?





RE: Quick Help on number of wires
So, no, you can't remove one conductor of the two.
RE: Quick Help on number of wires
Just to make sure, looking at the wiring diagram at the Motor Control Center (MCC), I could see three terminals (or contacts): T1, T2 and T3. Each terminal have two wires connected to it. The first wire from each terminal goes to one cable (field run) and second wire from each terminal goes to second cable. I guess, each conductor is carrying half the current.
You agree?
Thanks for such a quick response. Why is it that another pump with same HP has only one wire per phase then?
Pdshah.
RE: Quick Help on number of wires
RE: Quick Help on number of wires
Ideally, use the right size wire.
If using two wires, consider if you need to use two paralleled and ganged breakers - one for each individual wire. (And in this case, probably also ganged across the 3-phases too - total of six ganged breakers - maybe, yikes.)
The same sort of thing applies to paralleled contacts (a very common technique in electronic systems). It leaves an obviously rare but potentially dangerous opening for Murphy and his horsemen to ride in through.
I assume that the NEC would disallow using parallel wires without attention to this aspect of the over-current protection issue.
It strikes me that there is a fine line between parallel wires and multi-strand conductors anyway.
RE: Quick Help on number of wires
The NEC calls for no special provisions to parallel runs of cable, it's an accepted fact.
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Quick Help on number of wires
Very good point VE1BLL.
My question is answered, thanks a bunch to you all.
RE: Quick Help on number of wires
Iif the motor was originally star delta and is now used as delta only, the connections may be made in the motor junction box instead of at the MCC an one set of cables may be removed.
Be careful, you have not supplied enough information for us to say with certainty, star delta is a possibility, not a certainty.
respectfully
RE: Quick Help on number of wires