Overload Relay Troubleshoot/ID Help

[G-ManBart]

Make sure the information you’re following is from the manufacturer (now Siemens) not a vendor. Some companies make aftermarket products that aren’t quite as precise as the OEM products

No doubt. I can't find the heater charts on Siemens' website, but I have found it other places. Assuming I'm using the correct chart, it's closer to what I find on my machine, but still slightly different.

 

[G-ManBart]

It would seem to me that the problem is not with the heater (the coil of wire), but instead the problem is with the overload relay itself, the part which is heated by the coil or the contact parts behind the O/L assembly.

Yes, that seems most likely. It reset several times and then wouldn't, even after several hours of cooling time, so something isn't right.

 

[benmychree]

Another thing that strikes me is that the motor should not be experiencing full load amps when it is not really under full load It may be of interest to measure the current with a Amprobe or similar tong type ammeter.

 

[G-ManBart]

Another thing that strikes me is that the motor should not be experiencing full load amps when it is not really under full load It may be of interest to measure the current with a Amprobe or similar tong type ammeter.

The heaters in place were 4.5A heaters, so the motor wouldn't have to be more than about half load. I had a chuck mounted and was trying to fill and purge the variable speed system, which does put a load on the motor (fighting the expanding/contracting sheaves). The first trip took at least five minutes so I don't think there's a motor issue (I felt it and it was no warmer than ambient temp).

 

[projectnut]

Another thing that strikes me is that the motor should not be experiencing full load amps when it is not really under full load It may be of interest to measure the current with a Amprobe or similar tong type ammeter.

Keep in mind that startup load is often equal to or greater than full service load. That’s why overload heaters take time to come up to trip temperature. If the motor is in good shape and not overloaded the in rush current will subside quickly enough that the heater won’t come up to trip temperature.

 

[sdelivery]

Furnas stuff belongs in a furnace but that is just my opinion.
It is quite possible you have damaged the overload relay section of the contactor.This is where Furnas stuff is wimpy But first replace the heaters with the correct ones and attempt to reset the overload relay
I just experienced this phenomenon where correctly sized in use heaters would nuisance trip. I had cleaned the motor fan side because it was completely covered and wasn't pushing any air over the motor. I felt this is what started the overload tripping and they would simply push the reset and go. Test showed reasonable current levels, meggar shows good motor wiring and motor insulation.
You should always. Shut the power off to the contactor/overload and let it cool 5 minutes....but I live in reality and people just reset and keep going.
Point being the repeated reset and trip can do damage.
Be safe, Complacency kills or injurs

 

[projectnut]

I agree. I have a Bridgeport mill that was originally wired 440. I rewired it 220 but didn’t replace the N style heaters. They tripped several times on startup even though the motor wasn’t overloaded. A quick change to the proper heaters and they haven’t tripped in 20 years even under tough working conditions

 

[G-ManBart]

Update and thanks to everyone for helping!

I pulled both of the OL relays and think I figured out what happened. I took the first one apart carefully to see how they go together and I couldn't find anything suspicious. I cleaned the contact surfaces, put it back together and tested for continuity....seemed fine. As I was taking apart the second relay I noticed that the vertical spring-loaded piece which engages the gear secured by the melting alloy was twisted a tiny bit and stuck. All I can think is that while I was trying to figure out why it was tripping I pushed the reset as the alloy was hardening and it jammed the vertical piece between teeth....or something along those lines.

I cleaned the contact surfaces on the second relay, reinstalled both, replaced the wires, added power and bumped the switch forward and reverse for a few seconds at a time and the motor powered up as it should. Nothing looked burned or damaged so I'm hoping all it needs is a correct set of heaters at this point. Fingers crossed!

 

[G-ManBart]

Almost forgot to follow up on this one. I found a shop that specializes in electric motors selling NOS Furnas heaters they had listed as being 8.1 to 9.1A. I bought two, installed them and then ran the motor for half an hour or maybe a bit longer with no issues. I can't put a real load on the motor (compound and cross slide partially disassembled) but I suspect it's fine.