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

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Tran_Lap

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
 
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
 
Last edited by a moderator:
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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