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Old 09-26-2012, 10:18 AM   #1
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Default rewiring a pump panel from 3 to 1

Customer says he has 3 phase 480 line, but is running a single phase 7.5hp @ 240v pump. Obviously I know how to rewire the 3 motor starter with the solid state O/L to 1, however, the pump panel has 3p 70a circuit breaker disconnect.. is there a simple wiring solution from the breaker to the starter? or will i need to install and wire a phase convertor.... or.. simply do this pump panel with a drive instead of motor starter....
Dang I really need to go to control wiring school....
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Old 09-26-2012, 10:36 AM   #2
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If as you say, he has 3ph 480 available and a 1ph 240V pump, you have a primary problem with the voltage, not the number of phases. You don't need a "phase converter" to get single phase FROM 3 phase, you simply wire 2 of the 3 phases. But that still gives you 480V 1ph going to a 240V motor. Not going to work. So you need to buy a 480-240V 1ph transformer, preferrably 15kVA or larger. Then your 480V side becomes a branch feeder for the transformer and you therefore can most likely no longer use the existing breaker, because it will be a mag-only breaker as part of a motor starter. Then you will need another breaker down stream of the transformer in the pump motor circuit and if that existing starter had a 70A breaker in it, you might have too big of an OL for that motor, so that might need to change too.

Any chance he can go buy a 3 phase 480V pump? It will probably cost him less.
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Old 09-26-2012, 10:49 AM   #3
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If as you say, he has 3ph 480 available and a 1ph 240V pump, you have a primary problem with the voltage, not the number of phases. You don't need a "phase converter" to get single phase FROM 3 phase, you simply wire 2 of the 3 phases. But that still gives you 480V 1ph going to a 240V motor. Not going to work. So you need to buy a 480-240V 1ph transformer, preferrably 15kVA or larger. Then your 480V side becomes a branch feeder for the transformer and you therefore can most likely no longer use the existing breaker, because it will be a mag-only breaker as part of a motor starter. Then you will need another breaker down stream of the transformer in the pump motor circuit and if that existing starter had a 70A breaker in it, you might have too big of an OL for that motor, so that might need to change too.

Any chance he can go buy a 3 phase 480V pump? It will probably cost him less.
(face palming self) I totally overlooked the voltage issue.. i need a vacation.. Ironicaly he asked for an Allen Bradley or equivelent- I noticed "Rockwell" in your profile... mind if I PM you the details after I verify some more info on his application?
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Old 09-26-2012, 11:00 AM   #4
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Yeah I was thinking a transformer also. I'm guessing the motor is about 35FLA so your 480V 3ph isn't going to see anywhere near the 70A to trip the breaker. You would definitely need some protection on the motor side of the transformer. If you do go with a 480 3ph motor you will need a new starter and overload too. If you needed more precise flow control the drive would be a possibility. I'm biased toward the drive because I can make adjustments to how the motor operates without rewiring or installing new equipment. I haven't looked but I do recall working on some drives that have 3ph 480/3ph 240 line input driving a small single phase motor.
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Old 09-26-2012, 11:05 AM   #5
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(face palming self) I totally overlooked the voltage issue.. i need a vacation.. Ironicaly he asked for an Allen Bradley or equivelent- I noticed "Rockwell" in your profile... mind if I PM you the details after I verify some more info on his application?
Sure, go ahead. I don't deal directly with pump panels, I'm more of a VFD guy now, but I did pump panels for years so no problem.
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Old 09-26-2012, 11:10 AM   #6
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Yeah I was thinking a transformer also. I'm guessing the motor is about 35FLA so your 480V 3ph isn't going to see anywhere near the 70A to trip the breaker. You would definitely need some protection on the motor side of the transformer. If you do go with a 480 3ph motor you will need a new starter and overload too. If you needed more precise flow control the drive would be a possibility. I'm biased toward the drive because I can make adjustments to how the motor operates without rewiring or installing new equipment. I haven't looked but I do recall working on some drives that have 3ph 480/3ph 240 line input driving a small single phase motor.
You have to be careful using those VFDs that say they are for single phase motors. They can only be used on CERTAIN TYPES of single phase motors, PSC and Shaded Pole. They tell you that, but you have to read the literature BEFORE you buy it, and I for one almost never do that.
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Old 09-26-2012, 11:35 AM   #7
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If the service is 277/480volt wye, buck 277 volt to 240 volt.
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Old 09-26-2012, 12:29 PM   #8
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If the service is 277/480volt wye, buck 277 volt to 240 volt.
Great idea if it is a 4 wire service.
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Old 09-26-2012, 12:32 PM   #9
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probably cheaper to change motor to a 480v 3ph, instead of messing with transformer,...
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Old 09-27-2012, 12:45 PM   #10
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You have to be careful using those VFDs that say they are for single phase motors. They can only be used on CERTAIN TYPES of single phase motors, PSC and Shaded Pole. They tell you that, but you have to read the literature BEFORE you buy it, and I for one almost never do that.
Oh damn I never knew my pulse-mod VFDs couldn't run some types of single phase motors. I'm certain all the test motors in my shop were PSC. Looks like I'll have some homework this weekend if I'm not working.
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Old 09-27-2012, 12:57 PM   #11
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How will you comply with 110.3(B)?
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