How do manufacturers determine the 'rated' quantities for motors?

[yucheng]

TL;DR Summary

N/A

I'm confused with the term "rated". I checked this webpage though I am not confident about it's reliability.

Context: Motor ratings etc.

Does it mean maximum? Maximum in what regard? Heat produced/temperature? Is there a more reliable source on how manufacturers determine the 'rated' quantities? Does it take into account safety margins, tolerances etc? (I might be jumbling jargon!)

 

[scottdave]

I did some searching in the IEEE standards. They describe "rating" as what the equipment is designed to operate at continuously. I would link to it so you could read it, but it requires a login.

An example of voltage rating:

Maximum design voltage-to-ground: The maximum steady-state voltage-to-ground at which the high-voltage cable termination is designed to operate continuously under normal conditions.
NOTE—It is not intended that this maximum voltage limit be applied to transient overvoltages or unusual service operating conditions where the system voltage may exceed these values for only short periods of time.

 

[yucheng]

They describe "rating" as what the equipment is designed to operate at continuously.

Maximum?

 

[Tom.G]

Maximum?

Usually, but not necessarily.
A motor would have maximums for Voltage, Load, Temperature; it could also have minimum ratings for Temperature and Speed.

The 'Rating' is the operating region where the motor will meet its expected lifetime when the rest of the 'Ratings' are approximately met..

For instance a bicycle may be rated for a speed of 25mph (40kph). You can operate it slower, but at some low speed it gets so difficult to balance it falls over.

At a higher speed of 50mph (80kph) the front wheel may start to shake or the brakes may overheat and fail at a sudden stop.

Hope this helps!

Cheers,
Tom