Motor Heater "Trip" Curves

[big john]

I have a 480V 35HP motor with a full-load current of 60A. There's something causing it to bind, and it's drawing about 170A for several seconds at a time, but my overload heaters aren't opening.

I assume these are 75A heaters (60A x 125%, but I'll have to check). If so, is it normal for them to conduct this kind of current? Anyone know where I can find some "trip" curves?

Thanks.

-John

 

[don_resqcapt19]

The most common, Class 20, overload relay will hold 6 times full load for 20 seconds.

 

[jim dungar]

The industry 'trip' styles are:
Fast: Class 10, 6x for 10 seconds
Normal: Class 20, 6x for 20 seconds
Fast: Class 30, 6x for 30 seconds

Actual trip curves are available from the manufacturer but they are almost never used for testing of trip times (especially not for low level overloads).

European style devices are normally Class 10 and, as Don noted, North American ones are usually Class 20.

 

[big john]

That solves my "problem". Thanks for the help!

-John