Motor Protection Switch

[markdobson]

Hey everyone i have a question i hope i can get a little help with, i repair ice machines and other small commercial equipment but have never looked or worked on anything 3 phase, my friend has a problem with his coldroom as it keeps tripping what i believe to be a motor protection switch the make of the switch is an ISKRA MS25-4, the 3 phase power is going through this and when the compressor runs it trips this switch, sometimes it trips it after 2 minutes and sometimes it runs for 10 minutes before tripping it. Am i right to believe that this switch is just a breaker? The little dial is set to 4 amp so if 4amp is exceeded on the red, yellow or blue phase then this will trip? I have never come accross one of these before, i never had my tester but i am calling back to the job tomorrow, i ran the system with the compressor electrics disconnected and it did not trip the switch so i am sure the compressor is the cause, the compressor is a Lunite TAJ4519Z 3 phase, be great if someone can confirm what this motor protection switch actually does :confused:

[ABZ]

could be a faulty contactor,check for 415v through contactor with the comp tails pulled,if you have 415 through contactor i would say compessor is faulty.
that switch is an overload trip to protect compressor

[markdobson]

ok thanks, i will check contactor tomorrow, when you say overload trip what could overload it and cause it to trip if the compressor is not faulty?

[ABZ]

faulty contactor could cause single phasing to comp,causing comp to pull excessive amps.if you have 415v across red yellow and blue phases on bottom of contactor, you probably have a seized compressor.
reconnect comp and reset overload and run test.put your amprobe on the phases you should get the same on each phase.
also check run amps on comp name plate in case someone has adjusted the overload setting,some people do fiddle with things they dont know about

[install monkey]

overload setting should be 125% of the motor running current- if the compressor pulls 4 amp the overload shouls be set to 5 amp- dirty contacts can cause a higher operating current too