Reset Button

Hire an intern to reset the button.

You must be the same guy having trouble cutting off the motor line in the PLC? I can draw you a decent circuit if you want, or may be James stewart?

Stop trolling me and stop stalking me. Your head is shrinking to match your brain size, so you need to go drink a bathtub full of beer or something.

James: first it was Lyn, now it's you, I'm sure he'll get around to everyone eventually :)

On second thought, have him draw a circuit, then the membership can critique it.

First he has to learn how to hold chalk to the sidewalk.

deceiving and being deceived.

if it aint broke don't fix it. Just build a better one.

Or maybe you could just strike a pose on the sidewalk, and let someone else draw a chalk outline around you. Practice for when they really need to outline you later.

The design procedures at the organisation are insufficiently rigorous. Once the redesign has taken place, reassess the design procedures and change them so that everything is "right first time".

I don't understand why a thermal switch installed in a motor opens on loss of voltage (power failure).

From the circuit it looks like a loss of 24V signal to the K1 coil is causing the problem, not the motor.

Based on the circuit logic, you are a bit stuck (unless you alter the fundamental logic of the circuit to eliminate this problem). For example, take the motor overload and reset contacts directly to the PLC or DCS digital inputs, altering the programmed logic to include a latching and reset function in software rather than hardware.

Other alternatives are to prevent loss of 24VDC supply to K1 by adding a UPS or similar. Other options are available to add relay logic to your existing relay logic in order to eliminate the problem; if not carefully done, however, it could cause unintended circuit operation and different problems.

WTF is that supposed to be or do? Or am I missing the joke?

I suspect AP3 found a diagram online and said "Oh look! A DIAGRAM! One that mentions MOTOR! Think I'll use it!"

Alrighty then. It's been fun, but I've got to scream now.

<unsubscribe>

Think I'll use it!"

No - that is the problem - did not think before using the diagram.

Its some sort of monitor circuit with a loop integrity test function. Quite off topic as it doesn't relate to any solution I can think of or imagine.

I think it's a bomb!

I guess the thermal contact is normally closed and only opens due to over heat. If this is the case, wire the relay across the 24V line and if the power fails the K1 contact opens. When the power comes back on, the relay is again energised which will again start the motor. No reset needed. This contact is in series with the thermal contact so the motor will stop on an overheat problem.

This is unsafe. If the motor stopped due to overheat (and the rest of the control circuit was left in the RUN state), it would restart without warning when the temperature dropped. This could be when some poor unfortunate was poking around in the workings to try to find out why the motor stopped.

A motor should never restart without manual intervention (i.e. operation of a control).

Ahem: <...A motor should never restart...> after stopping on fault <...without manual intervention...> would be better, as motors start and stop normally in automated equipment all the time.

Give you that one. I was replying pre-coffee.

So you have never worked in an automated power plant, where pumps may turn on or off unexpectedly? No one is allowed under any circumstances to cross the skid plane unless the item has been locked out/tagged out (i.e.- removing all sources of stored, kinetic, or nascent energy).

OK, I finally read the remaining comments below that one. I need more coffee after that, and a cigarette. We stand offline, and unstruck today,

You can not just reset a thermal switch, it needs to cool off to normal operating temperature and then back again. It doesn't matter how many times you push a button, just won't work at all if it's hot. Kinda like "it's now or never" style and its a safety switch that cannot be by passed.

Is it a reset button or acknowledge fault button for diagnostic purposes?

Send us the full details circuit. That circuit does not show any information.