Contactor Overload Relay not working - need help

[John TenEyck]

I got my friend's 16" Zefam jointer running today with the upgraded static phase converter he bought for it. It comes up to speed in 3 seconds now and seems to run very smoothly. I wired it so we could use the machine's normal on/off switches. This SPC replaces a lower rated unit. When I installed that one I couldn't get power to the motor and traced it to a thermal overload on the contactor. I bypassed the contactor, temporarily, and the contactor closed when I pushed the start button and the motor started. I didn't fool with the overload today when I installed the new SPC, but I'd like to resolve the issue for peace of mind.

The contactor is a Telemecanique, made in USA which I didn't expect with that name:






Attached at the bottom of the contactor is this overload relay:



Which has this label on one side:






What's confusing to me is that the relay is rated for a normal range of 5.5 to 8 amps (now set at 8 amps, as I found it), but the motor has a FLA rating of 11.2 amps and draws around 10 amps when running with no load except turning the cutterhead. There is a reset button on the relay, the red button at the right in the photo, but it won't reset when I push it. The wires now connected to T1, T2, and T3 on the contactor were connected to the 3 lugs on the overload relay until I bypassed it.

The former owner ran it on 230 V 3 phase power. We're running it on 220V single phase power through a static phase converter. He claims it ran fine. If so, the relay must have been the appropriate size, though it seems undersized to me. This is a new motor, but of the same 5 HP rating and amp. draw (actually, marginally lower) as the one it replaced.

Anyone have any ideas of what's going on here? Any input is appreciated. Thanks in advance.

John

[Dan Friedrichs]

So while the motor might measure 10A (RMS) when only spinning the cutterhead, it's likely at a lower power factor. When you load the motor, the absolute value of the current may not change much, but the power factor will go up. That doesn't really explain your problem, but does explain why you have 10A without a load.

I would agree that it's odd that the relay is undersized. That said, if the previous owner had it working, it's suspicious that something else might be wrong.

Here's a wild idea - the SPC doesn't produce a very well-balanced 3rd leg. The overload may be detecting an unbalance and tripping. Try only using the overload on one leg, only: "loop" it around so that the output of ph1 goes up to the input of ph2, the output of ph2 goes up to the input of ph3, and the output of ph3 goes to the motor.

[John TenEyck]

Thanks Dan, The overload relay isn't tripping because I can't reset it. I haven't tried hooking it back up like it originally was before I installed the first SPC. I suppose I should try that now that I've installed the new SPC to see if it will reset. If that's gives no joy I'm willing to try your idea but need some clarification. Before I bypassed the overload relay, the wires now connected to T1, T2, and T3 on the contactor were connected to the terminals below it on the relay, I'll call them R1, R2, and R3. How are you proposing that I wire it to implement your idea?

John

[Dan Friedrichs]

Well, wait and see if someone smarter than me has a better idea - this just seems like an esoteric problem that bad ideas might be worth trying

Here's a sketch of what I'm thinking. You'd lose overload protection on 2 of the 3 phases, but that's probably not a likely failure mode...
Sketch.jpg

[Bill Dufour]

make sure the power to the coil is 240 from the wall not the generated third leg. The generated third leg is often lower voltage and controls will not like it.

[John TenEyck]

Thanks Bill. Yeah, the SPC instructions were clear on that point. I'm pretty sure I have it right, but it's worth another check.

John

[John TenEyck]

Thanks Dan. Glad I asked 'cause that's not what I had in my head. It's exactly what you described though, I just didn't have it straight. So many thanks.

I'm still wondering why the reset doesn't work; I don't see how your idea is going to work unless I can get it to reset. Maybe Bill has it right and I don't have the right power wires coming from the SPC to the control circuit. On the other hand, the on/off switches both work, the contactor closes (with the overload relay out of the circuit), and the motor runs, so .....

John

[Rollie Meyers]

That starter needs the overload relay replaced with one that can be adjusted to the rating of the motor, anything else is ignoring that the O/L relay is performing as it should as those relays are adjusted to the motors rated amperes. This is one disadvantage of IEC overload relays when the adjustment range of the O/L relay does not match the motor, unlike other types where the heater coils are replaced with the correct size, but they are going away because of the toxic metals they contain.

[John TenEyck]

Thanks Rollie. I agree, but the O/L relay apparently worked with the prior motor which drew 11+ amps.

John