Motor overload tripping

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electro7

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Electrician, Solar and Electrical Contractor
Hi,

Im not a motor guy so need some help. I have a compressor that has a contactor and overload heaters (see photo). The red button which I assume is operated by the overload heaters, keeps tripping. I changed out the overload heaters but it keeps tripping. I am now wondering if the heaters are under rated. Any other thoughts?
f3f252a69639381c390a7d0e1b184d98.jpg


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Here is a picture of the heaters and the breaker is also a 40A.
4054d6718c772be252b91109e5df7cb3.jpg


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Did the machine ever work properly with these heaters in place? Does it trip instantly or after a period of time? Have you tried removing the drive belt(s) and running just the motor? If the contactor trips with the motor unloaded, you probably have a faulty motor winding. If the compressor will run long enough to take current (amperage) readings on each phase, that will tell you a great deal. I'm sure you've checked for voltage on all three phases to rule out the possibility of the motor trying to start in a single-phased condition.
 
OldSparks has the first question that needs to be answered. The heaters are likely doing their job protecting the motor.

Does the motor ever start?

Check all the connections and make sure they are tight.
Uncouple the motor from the load and try.
Check the unloader on the compressor.
Check the amps.
 
There should be a chart on the cover or on the side of the enclosure. Match that heater number to the listed ampacity. Then check your motor name plate. If sized correctly. Then start trouble shooting.
 
Depending on some details that overload element is for a motor with a full load current of 21.8 to 24.2 amps or 22.5 to 25.1 amps.
 
Okay, thanks for all the info. I'll get some information and be back. Thanks again!!

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electro7 said:
Hi,

Im not a motor guy so need some help. I have a compressor that has a contactor and overload heaters (see photo). The red button which I assume is operated by the overload heaters, keeps tripping. I changed out the overload heaters but it keeps tripping. I am now wondering if the heaters are under rated. Any other thoughts?
f3f252a69639381c390a7d0e1b184d98.jpg


Sent from my SM-G998U using Tapatalk
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Looks like they are installed backwards/upside down.
 
ptonsparky said:
Only in that they were incorrectly installed.
Click to expand...

It’s been awhile since I’ve seen one of those style OL relays, but if the ratchet wheel is facing out, I don’t think they’d ever trip or reset, one or the other. Remember, the OP removed at least one of the elements for the picture. Maybe they were correct at one time?
 
Good catch, hillbilly !
electro7: When you reinstall them the correct way if I remember correctly you need to depress the red rest button as you set the heater in place so the ratchet will set properly.
 
augie47 said:
Good catch, hillbilly !
electro7: When you reinstall them the correct way if I remember correctly you need to depress the red rest button as you set the heater in place so the ratchet will set properly.
Click to expand...
Install all then press reset.

OP. Now is a good time to research eutectic alloys and how they relate to these and other older style overloads. Bimetal would be the other.
 
From what I was told, they had never been replaced, and since I thought they were the problem. I replaced them. When I did, I installed the new ones just as the old ones were, which is what you see in the picture. After installing the new ones, I depressed the red reset button in order for the motor to work.

It worked for a while but then started tripping again, just as the old ones were doing. It seems like the problem isn't related to the overload heaters because it's acting the same as when the old ones were in. It is an intermittent trip, and the owner was wondering if it had to do with high ambient temperatures outside.

I still need to get back there to get the nameplate info, etc.

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Those heaters don't typically go bad, Check to see motor FLA on the nameplate. Then there should be a chart inside that motor starter to say what heaters you use for that motor FLA rating. Get the heaters installed the right way. Amp clamp each phase as the compressor is running until high pressure cutoff. Highest reading right before cuttoff is what you want to note. make sure it does not exceed nameplate FLA.

You probably want to check what the pressure switch is set at. I find all the time that someone has jacked up the pressure settings because of poor peformance od some piece of pnumatic equipment. Usually it's to compensate for resistance to flow due to the piping/lines being too small.

Is this a single stage or a two stage compressor?
 
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