# single phase motors 240 or 120 vac



## myenergy (Jan 25, 2010)

I am trying to understand the reason why every body is so stuck on wiring single phase motors at 240vac. I dont see the math adding up to a reduction of watts used. in fact it's the same. and I am not convinced that the increased heat really makes a differance even over time. I have seen several of single phase motors wired for low voltage run for 15+ years. I still wire for high voltage just because everybody wants it that way. the reason I bring it up is with the advent of the 2008 code permanantly installed swimming pool pump motor 680.22.5.B. is now required specifically to be protected by GFCi breaker. before it was not.
a 15 amp double pole gfci 90.00 15 amp single pole gfci. 27.00. Im just sayin..........maybe I am missing something if so enlighten me


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## Dennis Alwon (May 9, 2009)

It is probably more important with commercial 3 phase system so that one can balance the load more easily. 

There are cases where connecting to 240 volts will keep the wire size smaller but other than that in a residence it doesn't matter. I have always heard that pumps are more efficient at 240v--- I don't know if this is true or not.


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## Speedy Petey (Jan 10, 2007)

The slight gain in efficiency is one thing. The other is voltage drop. 
Voltage drop is significantly lower at 240v than it is at 120v, and most runs for pool equipment are typically pretty long.


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## Dennis Alwon (May 9, 2009)

Speedy Petey said:


> The slight gain in efficiency is one thing. The other is voltage drop.
> Voltage drop is significantly lower at 240v than it is at 120v, and most runs for pool equipment are typically pretty long.



Very good point about the VD. A 120v pump at 100 feet and 18 amps needs a #8 wire for a 3% VD

A 240 pump at 100 feet and 18 amps only needs a #12. Now we know if it's the same motor the amps would be half for 240 so we are looking at 9 amps and a #14 wire.


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## Bob Badger (Apr 19, 2009)

You are right watts remain the same.

But a motor that requires a 30 amp circuit and conductors at 120 only requires a 15 amp branch circuit and conductors at 240 so the installation costs go down.

Also the current inrush is cut in half which means there will be less voltage drop, this may make the difference between seeing the lights on that leg dim a bit when the motor starts or the lights not dimming at all.

When given the choice I would always use the highest voltage possible.


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