Time curves for overload relays

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Pappy

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Where can I find time curves for CH and Square D OL relays.
Finding the FLA charts for sizing was not hard , but can't find the curves.
 

jim dungar

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Where can I find time curves for CH and Square D OL relays.
Finding the FLA charts for sizing was not hard , but can't find the curves.
As Zog said, more info is needed.

But, there is almost no reason to look at the actual trip curve of an interchangeable 'thermal unit' for an overload relay.
 

Pappy

Member
more specifically

more specifically

I am timing various thermal units for GE,CH, and []D starters. I have been successful in finding the motor full load current for these heaters. The customer is requesting to see the time curves for each ol relay to ensure my times are in range.Outside of GE, I haven't had any success in finding the curves I need. Any hints?
 

Jraef

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As Zog said, more info is needed.

But, there is almost no reason to look at the actual trip curve of an interchangeable 'thermal unit' for an overload relay.

Agreed.

If you can find them (and by the way, they are often in the Installation Manual), most often all you see is the standard NEMA I^2t thermal OL curve for whatever class you are looking at (see page 26 of this document). The reason is, they may not really want you to know how "sloppy" theirs is. UL requires that they trip NO LATER THAN what is shown on that trip curve class, but if it trips early, that's considered acceptable.
 

jim dungar

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Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I am timing various thermal units for GE,CH, and []D starters. I have been successful in finding the motor full load current for these heaters. The customer is requesting to see the time curves for each ol relay to ensure my times are in range.Outside of GE, I haven't had any success in finding the curves I need. Any hints?

Square D says "The curves are more accurate for high currents than for low currents. In particular, overload currents below 300% may yield different trip times. Conditions in the field may differ from those in a laboratory; the longer the trip time period, the more pronounced the differences."

http://www.schneider-electric.us/su...al-library/?event=detail&oid=09008926801181e7


http://www.schneider-electric.us/su...brary/?event=type.list&docType=sqd_trip_curve
 

Pappy

Member
Understood

Understood

Thanks guys. I was looking for some kind of documentation and/or graph to refer the customer to.That should do.
 
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