Could anyone please explain the att

[Universe_in_Flux]

Could anyone please explain the attached tripping curves on MN type thermal overload relay? Why are there two different hot and cold curves given? what is their significance?

 

[waross]

The cold curves are the characteristics when a motor is first started or a load is first applied.
The hot curves are the characteristics when a motor or a load have been running long enough for the temperatures to stabilize at operating temperature.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr Universe_in_Flux
U. " Could anyone please explain the attached tripping curves on MN type thermal overload relay? Why are there two different hot and cold curves given? what is their significance?"
C1. Fully in agreement with Mr Waross's learned advice.
C2. You see the "cold" pointing to two curves and likewise "hot" pointing to another two curves. It means that the tripping time is NOT one curve , but a band e.g. as [read from your attachment]; at 6 times set current:
a) for cold, the tripping time may varies between 24-48s,
b) for hot, the tripping time may varies between 13-25s.
Attention: above a) and b) tripping time are INCORRECT.. It is most likely a) 2.4-4.8s and b) 1.3-2.4s.. Reason being, see C3.
C3. The tripping time scale shown:
a) 10¹ is incorrect. It should be 10^-1 = 1,
b) the next shows 10² is incorrect. It should be 10¹ =10.
C4. Refer to IEC 60947-4-1/ 60947-5-1 for details on the band-width/the permissible tripping times at various times of set current for Class 10A, 10, 20 and 30.
Che Kuan Yau (Singapore)

 

[che12345]

Dear Mr Dear Mr Universe_in_Flux
First follow-up
U. " Could anyone please explain the attached tripping curves on MN type thermal overload relay? Why are there two different hot and cold curves given? what is their significance?"
C1 My sincere apology. There is an error in my earlier post:
"...C3. The tripping time scale shown:
a) 10¹is incorrect. It should be 10^-1 = 1,
b) the next shows 10² is incorrect. It should be 10¹ =10...."
above a) and b) are erroneous
It should be :
a) 10¹ is incorrect. It should be 10⁰ = 1,
b) the next shows 10² is incorrect. It should be 10¹ =10.
Che Kuan Yau (Singapore)

 

[Universe_in_Flux]

Thank you ,Bill and Che Kuan Yau ! For taking time out to reply and solving my query.