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Question for Gerald J
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Gerald J.
Posted 7/1/2006 22:15 (#23445 - in reply to #23399)
Subject: RE: Question for Gerald J


I figure 3 amps in the 7200 volt circuit for starting, 0.575 amps running.

The easy way to get the transformers is to get the REC to put in a separate service for the motor. No necessarily the cheapest.

You'd need a couple 5 to 10 KVA transformers, one for step up, one for step down. You may be able to acquire them from the REC or from W.W. Grainger, Westinghouse Supply, or a number of vendors of used transformers. Then you need poles and insulators and wire or a trench and direct burial wire. With the wire up in the air on poles, you'll want the transformers up on the poles too. The REC ought to be a good source of all the pieces installed, if they would.

But then if your running current is 18 amps, starting current is going to be more like 90 to 108 amps (5 to 6 times running current), not 50 amps, so the wire size needs 0.2 ohms loop resistance or 0.067 ohms per 1000 feet. 250,000 MCM aluminum or 3/0 copper. That's to keep voltage drop for starting down to 10 % which borders on making the motor have lengthy starts if the load is demanding. All that wire for a 20 amp circuit.

Gerald J.
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