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- Tennessee NEC:2017
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- Semi-Retired Electrician
Makes sense. I'll know more when I get to actually check it further.
Contactor Problem
- Thread starter Little Bill
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
That's my read on it. Heat concentration seems to be on that center pole right where the OL would connect to the contactor, then the heat rose, possibly warped the contactor and jammed it to where that center pole wasn't making good contact and it cascaded from there to a full meltdown.
Most likely that starter came from the supplier pre-assembled and was used that way. I always double check the connections when I get pre-assembled starters like that, I've seen too many where that factory connection was loose. Takes 10 seconds to stick a screwdriver in there and double check.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
I was able to check further on the machine and motor. I megged the motor and all three legs were in the Gig range. It is fed with 240V and that's what the motor runs on. The transformer inside the control cabinet was to get 120V. The coil in the contactor is 120V. I don't know what else uses the 120V.
I'm in agreement on loose connections causing heat build up. The contacts were stuck in like the coil had them pulled in. I didn't tear the contactor apart but I'm pretty sure the contacts are melted/welded together.
I'm in agreement on loose connections causing heat build up. The contacts were stuck in like the coil had them pulled in. I didn't tear the contactor apart but I'm pretty sure the contacts are melted/welded together.
phineas
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- therae@1122
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- I am an Electrician
- The burnt contactor could have been caused by factors such as overloading, excessive arcing, poor connections, or a faulty contactor itself.
- When using a Megohmmeter to check a motor, it is generally recommended to disconnect the motor from the power source, isolate it from the control cabinet, and test the insulation resistance of the motor windings directly. Seek professional guidance if needed.
That would be my first choice - loose connection(S)
As you know, 3 phase power fuses/CBs are there to protect the 3 phase feeder for short circuit etc. not the motor itself and does not act as the over load protection.
If the contactor is sized right, wire feeder size is selected correctly, O.L. circuit and its contacts wired up right, this problem is most likely caused by lose terminal connections. It could have been where the contactor and the O.L. blocked attached too, based on the picture. Sometimes, you will be no where what the O.L setting or the fuse ratings are to drop the coil or blow the fuses.
The O.L setting should be set correctly to begin with; I usually set it around 1.25% of the running amperage after monitoring it with an amp meter.
It is desirable to test the motor windings right at the pecker head if is easily accessible but not a must, assuming there is no other splices or connections in between. The proper way of checking the windings in reality requires the removal of the jumper connections that is used for high/low voltage selection. Testing in between the 3 phase winding and each phase to the ground.
In addition, checking it right on the motor itself gives you an opportunity to check the connections to make sure there are no issues with the connections in it.
If the contactor is sized right, wire feeder size is selected correctly, O.L. circuit and its contacts wired up right, this problem is most likely caused by lose terminal connections. It could have been where the contactor and the O.L. blocked attached too, based on the picture. Sometimes, you will be no where what the O.L setting or the fuse ratings are to drop the coil or blow the fuses.
The O.L setting should be set correctly to begin with; I usually set it around 1.25% of the running amperage after monitoring it with an amp meter.
It is desirable to test the motor windings right at the pecker head if is easily accessible but not a must, assuming there is no other splices or connections in between. The proper way of checking the windings in reality requires the removal of the jumper connections that is used for high/low voltage selection. Testing in between the 3 phase winding and each phase to the ground.
In addition, checking it right on the motor itself gives you an opportunity to check the connections to make sure there are no issues with the connections in it.
A contactor is usually single phase, not 3-phase.
The coil itself yes, the control portion of it,is that what you meant?The issue presented here is a contactor for a 3 phase motor. I have been in manufacturing for about 35 years, including Europe and the United States. I worked for a contactor, CB, fuse etc. manufacturer. I know them really well and installed 1000s of them. A contactor (Magnetic Starter, referred in the U.S for true motor starters can be used as well, NEMA size 0.1, 2,..Soft starters, VFDs etc. worked with every one of them)And that's it - just the contactor. Believe it or not I have around the world, mostly power electronics, for 40 some years.
I know you have been around
Just the contactor; we agree on sir. I appreciate your experience and other's here. Thank you for everyone's contributions. Very talented bunch here. The moderators are great!Laurra-7842
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- united kingdom
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- Services provider
Hey It seems you are facing a motor and controller issue. The motor is not the problem itself but rather a symptom. If the controller contacts weld together or fail to open properly during an overload it can lead to motor damage through single phasing. To resolve this check and repair the controller contact and inspect the wiring between the controller and motor. hope this help and best of luck resolve the problem...
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