Utilization Voltages, Nameplate Voltages, Service Voltages, +5%, -8% etc.

The numbers 460 and 575 are called utilization voltage (for motors and most other load devices/appliances) it’s what’s stamped on the nameplate.

The numbers 480 and 600 are termed service voltage, and components that serve load devices generally have this rating, like transformers, breakers and starters.

A system of 200 amps at 480V 3ø corresponds to a maximum capability of 166kVA, and 200 amps at 600V 3ø corresponds to a maximum of 208kVA. Generally, this is the advantage of higher distribution voltage, but of course there are tradeoffs. For higher voltage, the most obvious concern is that more insulation is needed to isolate ø-ø and ø-ground conductive surfaces. So 480V versus 600V is a ‘regional preference,’ and if you use one it’s likely that your neighbor does too. Generally in the US, 480V is probably more common. In Canada, 600V is used most often.

Voltage limits are in a sort of ‘treaty’ agreed upon by folks like electric utilities and appliance/equipment producers, and published and promoted by ANSI (or CSA to the north.)

The agreed-upon limits for 480V systems are usually 440-504V and for 600V it’s 550-630V. {Note that 460 and 575 fall within this range.} So the percentage limits are close to +5% -8%. Generally equipment won’t necessarily work most efficiently in the extremes, but it’s not supposed to be damaged either.

Transformers can be described as constant-power devices. For a given kVA, [kilovoltamperes] there is a corresponding ratio of voltage and current. 200 amps at 480V 3ø is about 166kVA, which in turn is equal to 160 amps in a 600V 3ø circuit. Roughly 1 hp = 1 kVA.

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