Please explain voltage ratings.?

Question

For instance, a pump I have is rated as 208-240V. I have had a few different electricians explain this differently. Is it as simple as 'anywhere from 208 volts to 240 volts? Or is amperage somehow included in this spec. Any and all information surrounding this would be appreciated.

Answer 1

You have it right

'anywhere from 208 volts to 240 volts'

And you can interpret this (and I would) as 'anywhere from a nominal 208 volts to a nominal 240 volts' which means it will operate from 208v -10% to 240v + 10%.

Current is not listed and has nothing to do with it.

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Answer 2

Yes, you are correct. The rating would mean that the pump can be operated anywhere between that range. It's performance will be affected by the applied voltage, that's all. For instance, and this is just an example, if the pump specs say it will pump 200 gallons per hour, that should be for a certain voltage rating, which it should list in the manual. If you go above or below that voltage, it will pump more or less.

Answer 3

Yes and No.

You can run the pump @ 208V to its rated power output (5kW for example)

Doing this would increase the current draw compared to running it at 240V.

You tend to find that power supplies have a modest variance depending on the distribution. Also you will get a volt drop depending on the length of the cabling run to the pump and its cross sectional area of the wire (impedance, resistive and reactive).

Basically if you have a 240V source and run a thinner cable for a long distance you may find that by the time you reach the terminals on the pump it has dropped to 220V.

If you have a 208V source and use the same cable run, you will not be able to run the pump at its rated output. The volt drop will actually increase because the FLC of the pump will be increased, further heating the cable run increasing its resistance.

So, yes its as simple as the voltage must equal the spec AT THE TERMINALS OF THE PUMP.