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one more electrical question

Thanks for all the answers on running 3phase over to the middle of my shop floor. One more question. Actually 2 more

1) The most I will be using at any time is the 3HP milling machine. After figuring about 750 watts/hp do I divide by three because it's 3 phase, to size the wire? My total run will be about 70 feet.

2) How do I pull off 110 volt to run the lamps attached to the machine? Just one leg of the three phase along with neutral?

Thanks for all of your help.

Ivan, Amateur, just moved to Oregon

Reply to
Ivan Vegvary
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IIRC, you should divide by sqrt(3).

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Reply to
jim rozen

Nameplate current draw will and should be the same on all three phases. You don't do any dividing or anything so silly. If your motor nameplate says 15 amps you should have at least #12 thhn wire which is good for 20 amps. You might also want to go out and purchase a National Electrical Code book as it has certain specifications as to what is required for motor branch circuits, both protecting the motor and the wiring.

tim

Reply to
TSJABS

A more useful guide would be UGLY'S electrical reference.

here's once source, if you do a search, you'll find many places to buy

Reply to
Jon Grimm

...

Yes, in a 208 3-phase system, there is 117 V from any one of the three legs to ground. To do this properly, you need four wires plus protective ground, all the way from the neutral-to-ground bonding point which is probably in your main service entrance. If you are wiring from a sub-panel that only has the three phases plus protective ground (a three-wire service rather than a four-wire service) it is NOT proper to use the protective ground as the low side of your 117 V loads.

Loren

Reply to
Loren Amelang

If he had the nameplate current available, I doubt he would be asking that question.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Reply to
jim rozen

Divide by sqrt(3) * (phase to phase voltage). IOW, divide VA by 360 for a

208Y system, after increasing the VA/hp to compensate for motor inefficiencies.
Reply to
ATP

Note also that he did not *say* 208 V (at least in the article to which you were replying. Of course, if he is who I think he is, then an earlier thread did show that it was 208 wye.

He may have Y (wye) (in which case it would be 208, and your advice would work), or he *might* have delta, in which case he has 220V between phases, and no certainty what the voltage to neutral would be on any given line. For that state, he would want a 240V/120V step-down transformer -- need not be too big, if all he is running is a couple of light bulbs.

Enjoy, DoN.

Reply to
DoN. Nichols

AS I remember, in a three phase Delta config, you have a standard single phase

240v feed (120-0-120) and a sec> >
Reply to
Ron Moore

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