NEMA rating standard is 460V but not 480V, why? 1

[NancyM]

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?

 

[buzzp]

This is because of voltage drop. They figure using 480V as the power then by the time this gets to the motor you should still have 460V.

 

[aolalde]

NancyM (Electrical):That is true of NEMA MG1 Std..

For motor application:

MG1 part 10.30 states voltages for polyphase machines at 60 HZ:
115; 200; 230; 460; 575; 2300; 4000; 4600 and 6600 Volts.

For Synchronous generators:

MG1 part 16.12.2 Voltage Ratings 60 HZ, Three Phase:
208Y/120; 240; 480; 480Y/277; 240/480; 600; 2400; 4160/2400

Certainly the difference is to allow some voltage drop from the incoming supply to the motor location.

The current is not the same it will change inversely proportional to the voltage provided.

For instance if the applied voltage is 480 Volts, Nameplate 10 amperes at 460 V full load becomes; 10*460/480 = 9.58 amperes for the same full load.

The limits per NEMA MG1 are +/- 10% of 460 V (414 min, 506 max.)

 

[aolalde]

By the way, it is possible to get motors manufactured to operate at nominal 480 Volts, 60 HZ, 3-Phase.

 

[busbar]

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.

 

[jbartos]

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.

 

[electricpete]

I agree with all the above.

Helpful to note that the standard utilization voltages (motor nameplate voltages) are typically 0.4% below the standard distriubtion voltages.

Distrubtion Utilization
13.8kv 13.2kv
4.16kv 4kv
480v 460v.

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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[charlierod]

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.

 

[jbartos]

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

 

[tarzan56007]

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.

 

[jbartos]

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.