voltage drop & derating

[jw441]

OC sanitation district has asked me to repull: 3-#10, 3P-30a-480v(blower), 3-#10, 120v(vapex & dupex) recepts, 3-#10 ground (for each item); all in existing 1"C(pvc undrgrnd), with a total distance of 700'. Then(same run) they want me to add: 3-#10, 1P-20a-240v(pump cntlr). They're calling out(dif 1"C, same lngth) 8-#14(24vDC)scada. My mind is jelly from correcting all the wire labelling for the entire job(15-20 characters per label), and appreciate any help on the wire calcs

 

[charlie b]

Re: voltage drop & derating

We would need to know the load on each circuit, not just the breaker rating. We would also need the type of conductor and the type of conduit.

 

[iwire]

Re: voltage drop & derating

700' on 10 AWG for 120 volt circuits?

It seems you have more than 9 current carrying conductors which will mean a 50% downward adjustment of conductor ampacity.

By the time you resize for that I do not think you will fit all of them in a 1" raceway.

My suggestion is to put the largest 3 circuit conductors you can in the raceway, put a 480 volt panel at the far end along with a small transformer to get feed the 240 and 120 circuits.

 

[steve66]

Re: voltage drop & derating

Running 24V SCADA wires 700' also sounds like trouble. I hope they aren't using any of those to drive relays. That may cause such a voltage drop that the relay won't pull in.

And at the other extreme, if the input impedences are very high, external noise may cause problems.


Steve

 

[tom baker]

Re: voltage drop & derating

You typicaly can't run 24 vdc scada in the same conduit as power if its a class II power limited circuit, even if all is insulated for 600v see NEC 725.54, plus the induction will cause problems. You need to find out what class circuit the scada is per Art 725.