Can someone explain why NEMA uses 460V as it's standard but not 480V? I am wondering why all motor specifications and catalogs list 460V but not the nominal 480V? If the nameplate data is for 460V, does that mean it will operate under the same conditions at 480V?
The relationship between nameplate voltage ratings and corresponding nominal system voltages varies with equipment types. You may want to review ANSI/NEMA Std C84.1-1995 boilerplate:
Voltage ratings and other characteristics of the various classes of 60-hertz electric equipment are established in other standards. A partial list of these standards is given in Annex E. For the principal types of electric utilization equipment, nameplate voltage ratings and the corresponding nominal system voltages to which they are applicable are listed in tables C1, C2, and C3 in Annex C.
Comment: The Utility voltage is often below the nominal 480V. This will help the motor running well if there is also the motor feeder voltage drop added.
In some cases, the Utility voltage is on higher side, e.g. over the weekend in the industrial/commercial area. In this case, the motor may actually have 480V or more across its terminals. Normally, the NEMA motor will safely work in 460V ±46V voltage window.
In an industrial plant everyone knows the distribution voltages and no-one knows the utilization voltages. I gave up trying to call them 460v motor, 4kv motor, 13.2kv motor. I just call them 480v, 4160v, 13.8kv and avoid the inevitable questions.
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Talking about motor voltages ... is it possible that power factor experiences a decrease by improving voltage profile (make voltages higher) in a feeder supplying motor branch circuits?
The question arises from the fact that at higher voltages magnetizing current will be higher and consequently power factor will be lower(if load current doesn't change substantially).
I think this depends on the type of load driven by the motor(fan, centrifugal pump, etc) and motor loading.
Suggestion: Decreasing voltage increases induction motor (U and T frames) power factor and increasing voltage decreases the motor power factor.
Reference:
"Electrical Engineering Pocket Handbook," by EASA
"Electric Apparatus Service, Inc.
630 Gibson Street, Kalamazoo, MI 49005,"
Charts on Pages 28 and 29
voltage specs are considered to be nominal, 440, 460, and 480 for example are all considered the same for all practicle purpose, The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.
Comment on the previous posting. Yes, the voltages 440V, 460V and 480V are sometimes considered the same for all practical purposes; however, the motor may or may not last for very long if the motor terminal voltage deviates from the motor nameplate rated voltage by ±10% for the NEMA type of motors.