Contactor Overload Trip Curves 1

[Hawkas]

Do contactor thermal overloads have the same type of trip curve characteristics as circuit breakers. And if so, how do you specify this, and is this information generally printed on overload labels??

 

[ScottyUK]

No. Thermal overload relays are listed as Class 10, Class 15, Class 20 and Class 30. The number relates to the tripping time at 6x setting. Most manufacturers publish the standard curves. I'm not sure which standard defines them - I'll have a look at work when I get there.


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If we learn from our mistakes I'm getting a great education!

 

[jraef]

In the US, the standard is carried by UL now under UL508 although originally it was NEMA standard ICS-2 (but NEMA is not an approval or testing agency, hence the adoption by UL). For IEC, it is IEC 947-4-1. They are not exactly the same, but close enough not to worry about the differences.


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[ScottyUK]

Thanks jraef.


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If we learn from our mistakes I'm getting a great education!

 

[Hawkas]

Thankyou both very much,

 

[oldfieldguy]

You can use an I^2*T curve wiht the "class" as the tripping time at 600% of rated current. It won't be exact, but it'll be close enough. If you're coordinating closer than the accuracy this statement produces, you're doing it wrong.

old field guy