Thermal Protection Relay - tripping
Thermal Protection Relay - tripping
(OP)
We recently installed a single phase, 10hp, vacuum pump. It has a Lavato thermal overload relay. It has a amperage range of 37-50 amps. The adjustment dial is set for the FLA rating of 50 amps. The relay keeps tripping. The first time you start the motor it will run for 4 or 5 mins and then trips. The second time it starts it will run for serval hours before tripping. The motor is only drawing anywhere from 28-33 amps. The motor was oversized to 10hp, the pump it runs was intended to have a 7.5 hp motor. Does it matter that we are under the thermal rating of the relay? It is rated for 37 amps and we are drawing only 33 or so. The relay is a Lavato 11RFN95350 or 11RF95350(couldn't read the number to be sure). At one point I did notice unbalanced current, about 23 amps on one leg and nearly 30 on the other. Any help would be appriciated. Thanks!





RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
I am sure it must be under some kind of warranty. Call the mfg.
RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
This is a 240v three wire (two 120 volt conductors and one grounded conductor) USA electrical system.
RE: Thermal Protection Relay - tripping
A circuit diagram would help - I can't quite imagine how this machine and its controlgear are connected. I would have guessed it was across the two hot lines with no connection to the neutral wire but from your description that is not the case.
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If we learn from our mistakes I'm getting a great education!
RE: Thermal Protection Relay - tripping
htt
It is started with a Lavato magnetic starter with a Lavato Thermal Protection Relay.
The motor is directly coupled to the vacuum pump.
RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
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If we learn from our mistakes I'm getting a great education!
RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
Alternately, line one may go through two poles of the relay in series and the other motor lead may return to line two through the third relay pole.
If you have connected the grounded circuit conductor to any of the motor leads, the relay may trip on unbalanced current.
This may be the case, or you may have a faulty motor.
Bill
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"Why not the best?"
Jimmy Carter
RE: Thermal Protection Relay - tripping
However... You were not sure of the part number of the Lovato OL relay. If that part number is 11RFN95 3 50, then it is actually NOT phase loss sensitive, it is a version they sell specifically for 1 phase applications. If so, then this is not the problem and it is likely defective. If on the other had it is the 11RF95 3 50 (no N) then it is the type that would trip without current running through all 3 phases. So that would explain what is happening to you. I suspect it's the latter.
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RE: Thermal Protection Relay - tripping
I have seen the pump struggle shortly after starting, a minute or two after starting, and then quit. This may have been the time I measured unbalnaced current.
Waross,
The third conductor is the equipment ground. It is bonded to the motor frame only. I am beginning to wonder if the thermal relay is tripping due to unbalanced current, as I have never seen it approach the 50 amp upper limit.
jraef,
Each of the two hot leg pass through the contactor and thermal relay. As you mention the third connection is looped. I am not certain which relay it is. As much as I hate to admit it, I am now having trouble seeing small things close up! I'll take a picture of the system and confirm the part numbers this afternoon. It was too dark last night.
Thanks to everyone. This is a big help.
RE: Thermal Protection Relay - tripping
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Thermal Protection Relay - tripping
The first maybe a bad run capacitor or loose wire. This or something else has caused the relay to trip within the first minute or two of startup. Maybe this was when I measured unbalanced current??? I can't recall exactly when it was.
The second was the vacuum pump was not getting sufficient oil due to a flow restricting valve. This valve is now gone. This would cause the circuit breaker and or rely to trip. This would happen much later. At least 30 minutes later..I am guessing as no one was present when it happened.
Both times resetting the circuit breaker and or relay would allow the motor to run.
RE: Thermal Protection Relay - tripping
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If we learn from our mistakes I'm getting a great education!
RE: Thermal Protection Relay - tripping
I don't know what a megger test is. My background is structural engineering. I had a little electrical training in college but not much.
RE: Thermal Protection Relay - tripping
A 'megger test' is an insulation test which is designed to find, among other things, weaknesses in the insulation system which lead to earth faults. Megger are well-known manufacturer of insulation testers and other test equipment, and their name has become synonymous with insulation test.
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If we learn from our mistakes I'm getting a great education!
RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
RE: Thermal Protection Relay - tripping
Each leg is at 119.5 volts with the motor running, 239 volts across the two.
RE: Thermal Protection Relay - tripping
I am still wondering if there is something else that caused the unbalanced current...bad run capacitor maybe? Either way the motor ran 40 hours straight Thursday and Friday without a problem. I'll watch and see if there are problems when it is restarted today.