Newbie to 3 phase overload relays

on a old kitamura cnc machine it has a motor starter relay with a Allen Bradley thermal overload relay that is connected to a oil pump that lubes the gears inside the head.

upon looking at the normally closed contacts on the overload relay. it had 100 volts on one side and nothing coming out the other. showing that it was tripped.

i pressed the reset button and the contacts on the overload relay closed again like they should be and the motor starter contractor pulled in,..

but the oil pump still didnt start up.upon checking the phases voltage before and after the overload relay.

i had 88 volts on two phases and 110 volts on one phase coming out of the contractor going into the overload relay.

on the other side of the overload relay. i had 110 volts on the same leg. but only around 2 volts and the other two. is this a bad overload relay?

i took it off of the contractor and checked for continuity across the relay and 1 phase is closed while the other two are open.

i think this is not normal just hope someone can confirm it. the other ones on the machine i checked and they are all closed on all three legs.

could my pump be killing the relay or is this something normal to happen over time?

Sounds like a bad OL relay or the relay is not resetting. Take the heater off the relay and look inside. When you operate the reset a ratchet arm should move from one side to the other and at the same time the OL contact should close. Check this with and ohmmeter. Look at the heater module, there is a ratchet gear that should not move when the heater is at room temperature. When the heater warms enough to allow the solder in the heater module to melt, then the ratchet gear will free wheel, releasing the ratchet arm and opening the contacts. When you reassemble the heater to the OL relay make sure the ratchet and ratchet arm are engaged.

Tom

A photo would help, but it sounds like you have an AB 709 style starter with three separate overload assemblies.

First thing is to check for full three phase at the starter line side. Measure only from line to line, not ground. Should have full voltage every combination.
If you only have single phase, that's the beginning of the problem, correct this first.

Remove the heater elements and look for overheating, discoloration and charred plastic around the heater area. If burned it will likely need replacement.

Measure the heater elements resistance while uninstalled, all should be at near zero ohms. Should get the same reading across them when installed. It's easy for small rated heaters to get thermal damage from repeated overcurrents and multiple resets.

The overload contacts (N/C) should be closed when the reset lever is cocked on the ratchet pawl. Make sure that the ratchet pawl's do not rotate with normal finger torque, they should be solid and not rotate, until overheated.

Lastly, with the motor wiring disconnected, check for the full line to line voltages at the load side of the starter. Do not measure to ground.

If all of that checks good likely you have a bad motor or load wiring.

SAF Ω

What type of OL relay you have has nothing to do with having continuity through the OL relay. You should ALWAYS have continuity through the power current sensing portion, the only thing tht "opens" is the control circuit. So if it is truly JUST* an OL relay and you are open in any power pole, it is seriously compromised and should be discarded and replaced. If it gets that bad on a melting alloy OL relay, as are used on 709 and 509 starters, the solder will have leaked out and might cause further damage. Just replacing the heaters puts you at serious risk of starting a fire. If it is an IEC or Solid State OL, there are no replaceable parts.

* However... It is really just an OL relay? Or is it a Motor Protective Switch mounted ABOVE the contactor, which has the OL relay built-in but also a complete switch mechanism? If so, then it WILL indeed open the circuit. But it should open ALL THREE poles, never just two, which then means one pole is welded closed and it too must be discarded and replaced.