3 ph motor magnetic contactor switch

Greetings:

I have a shaper with a 3 ph 380 v 50 hz motor equipped with a circa 1970's Siemens magnetic contactor switch. The contactor has a coil which is energized by a remotely mounted switch. My problem is that the contactor does not close when the coil is energized by the remote switch. The coil circuitry reads 27 volts, the coil is marked 220v 50hz. The contactor stays engaged when pushed in by hand, and the shaper works as designed until switched off. Only the remote switch The coil has two wires, 100% resistance (zero continuity) when measured across the two wires. One coil wire is attached to a thermal overload device mounted to the magnetic contactor, which appears (at least mechanically) to work fine.

The magnetic contactor has a label stating that one should look at the coil to ascertain control voltage. I have read on the internet that control voltages will often be lower than mains voltage, using a step down transformer. I have looked all over the machine and can't find a transformer. I can't figure out why there would only be 27 volts in this particular circuit... all wiring is in good shape with no breaks externally evident, and no transformer. I'm tempted to supply 220 v to the coil (after all, it's labeled 220v), but want to refer to the expertise here on the newsgroup before I chance burning the coil. Would zero continuity indicate a bad coil?

There are other circuits present on the machine in the form of on / off switches related to table travel. All have 220v. The only place 27 v is present is in the circuit that energizes the coil. The reduced voltage makes sense to me, since it would seem unwise to supply 220v to a remotely mounted control switch that is, literally, the closest the operator comes to the electrically energized parts of the machine during use. The remote control switch is normally off, spring loaded momentary on when pressed by the operator.

Regards, Jim Brown

Reply to
Jim Brown
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The coil is labeled for 220V so yes you can run 220V right to it. My guess is that you have a bad switch or loose/corroded connection somewhere causing voltage drop. Gregg

Reply to
Greg O

I don't understand what you mean about the "neutral" wire. There is no neutral in 3 phase. The problem you are having , is a bad wire or bad connection at the "stop" switch.

Reply to
ButcherMD1

Greetings:

The equipment is in Germany. 3 phase power supplied to most houses, as well as businesses... wish they would do that in the USA. I don't know enough about the subject of 3 ph power to articulate the neutral and may be mis-naming it, but there typically is a 'neutral' (often blue color), three hots (often one brown and two black wires), and one ground, for a total of 5 wires. Measured across hot legs one gets 380 v, measure from a hot to neutral or ground, one gets 220 v. The Germans will wire up their houses using the blue wire (neutral?), one of the hot wires, and ground...

Thanks for the replies, I really appreciate the problem solving power of this NG.

Regards, Jim Brown

Reply to
Jim Brown

Jim, Since the contactor stays latched in when engaged manually, I would think the coil is fine. You must have a bad connection in the control circuit. Sometimes screw-down connectors will get corroded, etc., and cause a problem like this .. .. sometimes even rusted connectors will be present. Trace the coil activation wires from one side of the coil, through the start & stop switches and back to the coil to make sure *all* connections are good and your problem should go away. You could even jumper (momentarily) the start button connections to see if the contactor pulls in. It could be internal to the start button. Ken.

Reply to
Kenneth W. Sterling

Greetings:

Thanks for the advice Ken, that's exactly what I did. Found a dirty switch, one of those with a roller on it that translates a cam action to a spring loaded plunger. The switch contacts were dirty, with some pitting of the sort you might see on an old VW points. Cleaned them up and restored the circuit... but wait there's more. The machine still wouldn't start, still no 220v to the coil. Examined the same switch that was dirty, since something had caught my attention earlier. It turns out that the switch only completes the circuit as the main drive engagement lever is moved from one position to another. There is no adjustment for this roller switch on the cam, so I figure that's the designed function. So in summary (and if I had the instructions they might read something like this, except in German), to start the machine, press the remote starting switch while engaging the main drive lever. The switch is, of course, conveniently located on the main drive lever.

Regards, Jim Brown

Reply to
Jim Brown

Is 27 volts the reading you get *across* the coil with the coil in the circuit? Or is that what you read between the wires disconnected from the coil? If there is a high resistance elsewhere in the circuit, you might only see

27 volts *under load*, but with the coil disconnected, you should see 220 volts.

What scale are you using on the ohm meter? The coil should have a resistance of several hundred ohms. That might be off scale on a simple continuity tester, but the resistance can't be infinite if the contactor will hold in, ie some current has to be flowing.

What is the resistance through the contacts? If you don't measure it, you won't know. High resistance anywhere in the series circuit can cause a voltage drop so you won't get full voltage at the load (coil).

Gary

Reply to
Gary R Coffman

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