# USA domestic power supplies

I'm being asked to supply a high power electrical device to run on a US domestic supply. Ideally I'd want 240v input (120v is too low)
In some place on the web I read about 120/208v being available - the higher voltage being used for cookers/dryer etc
These voltages being the the ratio of root3:1, seem like our UK 240/415v phase to neutral and phase to phase voltages.
Elsewhere I read about centre tapped transformers being used to provide the 120v which would make the higher voltage 240v.
TIA
Bob
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On Sat, 11 Oct 2014 10:26:42 +0100

I'm sure someone with more knwoledge will come along, but in my experience, a US domestic supply has two phases plus a grounded neutral. Each phase goes to one side of the breaker box, with loads connected between it and ground, and the idea is to split the load between the two so as to be balanced. Connecting across the two incoming phase wires gives 240 volts, which is indeed used for cookers, driers, etc. Three-phase can be provided, such as for lathes, compressors, etc, but at an extra cost. Remember that they use 60Hz, as well.
I maybe wrong, but I associate 415 volts with Canada, for some historical reason.
Hope this helps.
--
Davey.

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On Sat, 11 Oct 2014 10:26:42 +0100, Bob Minchin

Greetings Bob, Most houses in the USA have single phase supplied. Nominal 240 volts is supplied from a center tapped xmfr, with the center tap being grounded at the house inside the circuit breaker panel. This center tap is called the "Neutral" because there is no potential voltage between it and the ground. So only two voltages are available, 120 between one leg and the neutral and 240 across both legs. If 3 phase is available then depending on how it is wired 208 volts is available. Since you need power from a domestic supply you had better supply a device that uses 240 volts. In rural areas in the USA it is not unusual for the voltage supplied to be 10% or more higher or lower than nominal, depending if you are at the end of the line or not. In my case the voltage supplied gets as high as 260 volts. The power company says it is within tolerance, but I had to put buck transformers on one CNC machine because the spindle drive couldn't handle the higher voltage. And even though I am less than 1000 feet from three phase power there is only one phase fed down the road I live on. This is normal for the USA. Cheers, Eric
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snipped-for-privacy@whidbey.com wrote:

Bob
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On Sat, 11 Oct 2014 21:36:26 +0100, Bob Minchin

You're Welcome Bob. Eric