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Discuss 51 & 49 function relay in the Commercial Electrical Advice area at ElectriciansForums.net

T

Tran_Lap

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Hi all

New to the forum, can everyone help me to explain the difference between 51 and 49 function relay incase motor protection.

Thank you
 
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D

DanBrown

  • Thread Starter Thread Starter
  • #3
What do you mean exactly 51 & 49??, is this on the contactor overload??
 
G

Guest123

  • Thread Starter Thread Starter
  • #4
Hey.

With regard to motor protection there are a number of different relays that have different jobs.

Function 49 is overload protection
Function 51 is locked rotor protection.

There are lots of others - 50 = phase fault protection
50N = earth fault protection
50 + 51N = Time overcurrent with thermal in built.

You can also get harmonic protection etc etc

Hope this helps

Cheers
 
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T

Tran_Lap

  • Thread Starter Thread Starter
  • #5
my understanding 51 using for overcurrent protection, but the reason of overcurrent is overload, 49 is thermal relay and the reason is overload too. So, can I use one of them for overload protection? when do I use both ?

thank you
 
Last edited by a moderator:
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