Voltage drop at 500 ft..

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sparkync

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Customer has a outside "fountain pump" with a 1/2 hp motor. The length of the run is approximately 500 ft. I've punched it in 2 online calculators, and one tells me it would take #4 size copper wire. Seems way big. Another calculator says the voltage will only be 118 volts on #12 wire.
Don't seem to be consitant. Which one is right you think?
Thanks
 
Motors abhor low voltage. What did you use for load current?

Remember that the current (and resultant voltage drop) will increase as the voltage drop rises.
 
I put in 120 volts for voltage and 10 amps first for the current the first time for the 1/2 hp. motor. I also used 12.5 amps after taking 125 % one of the other times I calculated it.
 
I'm not sure at this point, but I think it is continuous. It's is a "fountain pump". I calculated it again on another online calculator, and it came up with the same thing, #4 AWG wire :(
 
Just boost voltage cost less than wire. Could have him get two pumps and multi-wire circuit so they’re both running at the same time. Cut vd down a lot though it’s an extra wire
 
Can you use 208 or 240 volts instead of 120 (many pool pumps are 208 or 240, so maybe they will have this fountain pump that way)? #4 cu seems about right to me. Maybe #6. A motor's current depends on the work it is doing, but pumps usually compensate for pipe losses and head by moving more or less water. The difficult thing to know in advance is whether this 1/2 HP pump is taxing the motor at about 1/2 HP. Is there an existing pump where you can measure the load, or is this new?
 
This is a new pump. I'll have to get back with him for more information. Thanks for your help. He may just have to not use the pump. I think it's more for decoration than for actual "need". Looks like it's more trouble than it's worth:)
 
As Sue said, can it be exchanged for a 240v version of the same pump?

I thought about a 208v pump on 240v with voltage drop, but it would start out at a higher current.
 
I'm with @suemarkp . Motors are rotating transformers. It makes far more sense to use a motor which can operate at the 240V available in a residence then to use any sort of transformers. With a 120V motor, you are going to need #4; maybe could get away with #6, but motors are not happy with low voltage. With a 240V motor you will be happy with a #10.

If you need to stick with a 120V motor, and elect to use a transformer, I'd suggest running a 240V circuit and using a 240:120V step down transformer near the motor.

-Jon
 
AC\DC said:
Small transformer and boost voltage up and to compensate for the vd
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Not worth the hassle for this application. Transformer + Disconnects + GEC + a place to mount all the gear + transformer losses for the life of the install even when the pump isn't running..... Pull some bigger wire and be done. There are precious few times when stepping up the voltage for a single small load pays off.
 
sparkync said:
Customer has a outside "fountain pump" with a 1/2 hp motor. The length of the run is approximately 500 ft. I've punched it in 2 online calculators, and one tells me it would take #4 size copper wire. Seems way big. Another calculator says the voltage will only be 118 volts on #12 wire.
Don't seem to be consitant. Which one is right you think?
Thanks
Click to expand...
I'd check on getting a 240V motor first, but I disagree with the others that voltage drop on a 120V circuit is a problem. That pump will be fine at 115V. It's not going to pull 12.5 amps ever, and I bet it pulls less than 10. I'd pull 8AWG and be happy. Even if you went ahead and pulled 4AWG that's gonna be a better deal than the cost of a transformer and all the extra work to set it up.
 
And don't forget, since this is a voltage drop issue, all 3 wires need to be the same size (EGC gets upsized to same as ungrounded conductor(s)).
 
I'd pull 4 AL in a 1 inch if the service is consistently 123~v to ground. Best would be a tiny little sub like a 2 space that makes it available for a second circuit if needed. If the service is a tad low I'd do 2awg AL or the 4 copper mentioned
 
For sure, 240v will be better. A small buck boost transformer can help if you have a 240v motor, or another option is a 240v to 120v transformer with taps you can adjust. An often overlooked option can be to use an Automatic Voltage Regulator, paid for with some of the savings on the wire.
 
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