Overload Relay Troubleshoot/ID Help

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G-ManBart

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Okay, this one is entirely on me, and now I'm looking for a bit of help. I'm far from an electrician, so I'll apologize in advance if I use a wrong term/description.

I've been working through evaluating my recent project lathe purchase (Clausing 6913) to see what's good, what needs to be fixed, etc. The machine was originally set for 460V and I have 230V from my RPC. The machine is configured with a single-phase F/N/R drum switch and a magnetic motor starter as well as a control transformer to provide the 120V for the drum switch. I reconfigured the motor leads and connections for 230V as well as the control transformer connections and fired up the RPC...everything seemed to work, but I only ran it for a short period of time.

My next step was to try the variable speed system and had the machine running when the overload tripped. I figured I did something wrong in the wiring so I checked the connections back to the RPC, reset the overload and it started back up. A few minutes later the overload tripped again (this should have been a clue). I pulled the cover off the magnetic switch box and started checking connections there. Reset the overload and it started up again....ran for a few minutes and tripped. At this point I remembered I hadn't even thought about the heaters in the thermal overload relays. Sure enough, the heaters were 4.5A and the motor draws 9A. Problem is, the overload won't reset now. I'm assuming the multiple resets so quickly damaged the melting alloy pot, or something similar. Before I start pulling things apart I figured I would ask the experts. I also can't see any information on the side of the OL relays to see if I can find replacements....might have to remove them for that. The relays use type H heaters if that helps.

If anybody can point me in the right direction on the OL relays to see if there's anything that might be repaired/replaced, and what model they might be, or if there's something that would be a direct replacement. Here are a couple of pics....the overall layout and closeup of the OL relays.

IMG_4203.JPGIMG_4204.JPG
 
I'm guessing you burned out the heater. My Sheldon lathe uses a similar Furnas system. It has a 2 hp motor which supposedly draws 6.3 amps when wired 230-volt 3 phase. As such it uses H28 heaters which are rated for 6.19 to 6.74 amps. I don't know the size of the motor in your machine, but if it's wired correctly, isn't damaged, and is drawing 9 amps it should be using H31 heaters. The heater size is stamped on the anchor plate. It's hard to see, but it appears that the one on the left side is stamped H25 which would be correct (4.29 to 4.86 amps) if the motor is supposed to draw 4.5 amps at maximum load when wired for 460 volts 3 phase.

According to performance charts a motor wired 460 3 phase draws 1.27 amps per horsepower. The same motor wired 230 3 phase will draw 2.5 amps per horsepower. It appears your heaters need to be upgraded. There are currently several listings for H31 heaters on eBay. Most are around $10.00 plus shipping.

When I purchased my machine 7 years ago the previous owner alerted me to the fact that Furnas brand starters were notoriously weak. In the case of my lathe, he suspected they would need to be replaced within a couple years. Because the Furnas components are harder to find and considerably more expensive, he suggested when the time came, I rewire it using Allen Bradley controls. I respected his assessment since he was controls engineer who worked for Furnas designing systems for the Sheldon machines.

I purchased a NOS control panel with reversing starters to be ready. 7 years later it's still sitting on the shelf. Hopefully it will be sitting there another 7 years or more. At least I'm prepared should that time come.
 
projectnut said:
I'm guessing you burned out the heater. My Sheldon lathe uses a similar Furnas system. It has a 2 hp motor which supposedly draws 6.3 amps when wired 230-volt 3 phase. As such it uses H28 heaters which are rated for 6.19 to 6.74 amps. I don't know the size of the motor in your machine, but if it's wired correctly, isn't damaged, and is drawing 9 amps it should be using H31 heaters. The heater size is stamped on the anchor plate. It's hard to see, but it appears that the one on the left side is stamped H25 which would be correct (4.29 to 4.86 amps) if the motor is supposed to draw 4.5 amps at maximum load when wired for 460 volts 3 phase.

According to performance charts a motor wired 460 3 phase draws 1.27 amps per horsepower. The same motor wired 230 3 phase will draw 2.5 amps per horsepower. It appears your heaters need to be upgraded. There are currently several listings for H31 heaters on eBay. Most are around $10.00 plus shipping.

When I purchased my machine 7 years ago the previous owner alerted me to the fact that Furnas brand starters were notoriously weak. In the case of my lathe, he suspected they would need to be replaced within a couple years. Because the Furnas components are harder to find and considerably more expensive, he suggested when the time came, I rewire it using Allen Bradley controls. I respected his assessment since he was controls engineer who worked for Furnas designing systems for the Sheldon machines.

I purchased a NOS control panel with reversing starters to be ready. 7 years later it's still sitting on the shelf. Hopefully it will be sitting there another 7 years or more. At least I'm prepared should that time come.
Click to expand...
The heaters are marked H25, which is the 4.5A version and you're correct that they should be 9A heaters. The motor is 3hp and the data plate says the full load amp draw is 9A on 230V (4.5A on 460V so it all makes sense).

I pulled both heaters out and they look okay, so I'm not sure they're actually burned out...seems like solid wire. I don't see why burned heaters would prevent a reset, but maybe I'm missing something. I also don't know if the reset will actually work in the absence of input power. I'm pretty sure the last time I tried (after a long cooling period) I didn't have the RPC running.
 
mksj said:
A H33 heater is rated for 9.18-10A, H25 is 4.01-4.48.
www.pillarsurplus.com

Furnas Overload Thermal Unit Heating Element Type H H33

Furnas Overload Thermal Unit Heating Element Type H H33
www.pillarsurplus.com

Not sure on the reset, they usually are not dependent on power, they are thermal.
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Things may have changed over time, but the Furnas sticker in the electrical cabinet on my lathe states the H31 heater should trip with a maximum draw of 9.65 amps. The H33 has a range of 10.8 to 12.3 amps. In this case if the motor is only supposed to draw 9.0 amps at full load, I would stick with the H31 heaters. The highest I would go would be an H32 with a range of 9.66 to 10.7 amps. Even then you could be overloading and possibly damaging the motor before it trips.
 
projectnut said:
Things may have changed over time, but the Furnas sticker in the electrical cabinet on my lathe states the H31 heater should trip with a maximum draw of 9.65 amps. The H33 has a range of 10.8 to 12.3 amps. In this case if the motor is only supposed to draw 9.0 amps at full load, I would stick with the H31 heaters. The highest I would go would be an H32 with a range of 9.66 to 10.7 amps. Even then you could be overloading and possibly damaging the motor before it trips.
Click to expand...

I think things have changed slightly over time. The sticker on this cabinet shows the H31 having a range of 8.91 to 10.0A. When I did an online search I found H31 listed as 7.35 to 8.21A. I found online listings for H32 heaters with a range of 8.11 to 9.17A where my sticker shows 10.1 to 11.0A.
 
Most motors have a service factor of 1.15-1.25, the heaters are specified for 1.15, so he should check his motor. Not familiar with the Furnas heaters, but usually there is some margin above the rated voltage/current and/or specific heater elements, I was using table 135 for the heater element amperage. Motors amps is also dependent on the line voltage and motor voltage, this is the table they provided, but ok to be a bit conservative.

1691179117224.png
 
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
 
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.
 
mksj said:
Most motors have a service factor of 1.15-1.25, the heaters are specified for 1.15, so he should check his motor. Not familiar with the Furnas heaters, but usually there is some margin above the rated voltage/current and/or specific heater elements, I was using table 135 for the heater element amperage. Motors amps is also dependent on the line voltage and motor voltage, this is the table they provided, but ok to be a bit conservative.

View attachment 455997
Click to expand...
I don't recall what the service factor is on that motor, but full load amps are listed at 9.0A for 220V. My RPC is putting out 245-255 depending which legs you measure.
 
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