IEC Vs Nema for motor nominal voltage vs rated voltage

[Stuq27]

Hi Everyone,

I must apologise for asking a similar question to several others but none quite answers my query.

We have a customer who specified to us the nominal voltage for a motor to be 480VAC and the name plate voltage to be 460V

We work to IEC 60034 and so the motors we are specifiying are rated at 480V. The customer is used to working with NEMA so can't understand why we can't utilise 460V motors to match some other plants they have.

We have pointed out that the guidelines are different in a few different ways but including the quotation below which specifically points to 480V in IEC.

"For three-phase a.c. machines, 50 Hz or 60 Hz, intended to be directly connected to
distribution or utilisation systems, the rated voltages shall be derived from the nominal
voltages given in IEC 60038.?


Is there anyone here who can give me some advice on how i can explain this in a clear way to a Nema user

Regards

Stuq

 

[petersonra]

In the US the nominal voltage is 480V but the motors are labeled as 460V, presumably to account for voltage drop.

If the motor is coming here, it probably needs to follow this practice.

If it is going to end up elsewhere, whatever practice is followed there seems appropriate.

We get motors here that have all kinds of strange labels on them from Europe.

 

[Jraef]

I think you are misinterpreting. IEC 60038 does not read any differently than the ANSI C84.1 specifications for SERVICE voltages in 60Hz systems. What NEMA motors are designed for is called the UTILIZATION voltage, which as petersonra says, is intended to allow for voltage drop between the service entrance and the equipment connection. So the 460V Utilization Voltage Rating of the motor is DERIVED from the 480V Service voltage. If you look at your statement, it says the same basic thing, "the rated voltages shall be derived from the nominal voltages given in IEC 60038.", just without mentioning the lower utilization level.

Ultimately, if the equipment is going to end up in North America I would adhere to the standards and conventions that the users will expect.

 

[Smart $]

re:

In the US the nominal voltage is 480V but the motors are labeled as 460V, presumably to account for voltage drop.

From: http://www.reliance.com/prodserv/motgen/b7095_1.htm

Voltage. The voltage at which the motor is designed to operate is an important parameter. Standard voltage for motors built to NEMA MG 1 (1987) are defined in MG 1-10.30. One common misapplication is of motors nameplated (rated) at one voltage but applied on a different voltage network using the + 10% voltage tolerance for "successful" operation. Nameplate-defined parameters for the motor such as power factor, efficiency, torque, and current are at rated voltage and frequency. Application at other than nameplate voltage will likely produce different performance.


​

It is common for manufacturers to nameplate a wide variety of voltages on one motor nameplate. A common example is a motor wound for 230 and 460 V (230/460 V) but operable on 208 V. this 208-230/460 V motor will have degraded performance at 208 V. Another common misconception is to request a motor rated at network voltage; for example, at 480 V. The NEMA standard is 460 V. The voltage rating assumes that there is voltage drop from the network to the motor terminals. Thus, the 460-V motor is appropriate on a 480-V network.​

 

[Stuq27]

Hi guys,

Some good points here and to be fair I see both points of view but there is some unclarity the IEC has a recommendation for a maximum voltage drop to the utilization voltage of 4% with this in mind then starting from 480V and rating the motor for 460V isn't possible. I also see the nice table you guys have in Nema which leaves less room for discussion.

So while it doesn't say you can't do this in IEC it does try andguide you away from this approach.

Any thoughts?

Stuart

 

[GoldDigger]

In the US we compound two different factors: the voltage sag below nominal from the utility and the voltage drop on the customers feeder and branch wires. Together they reach 460V nominal.
If you instead assume that POCO is not allowed to deliver anything less than 480V to the service point, you will have a real world problem.
The final argument is to look at the allowed input voltage range for a NEMA 460V motor.

Tapatalk!

 

[ActionDave]

So while it doesn't say you can't do this in IEC it does try andguide you away from this approach.

Any thoughts?

Stuart

There is no such thing as a 480V NEMA motor here, only 460V. I have never seen a problem connecting a 460V motor to 480V. Most of the time the actual voltage is more than 480V. More like 500V or better.