Is the 2 cables in the connector blocks the thermal OL

i would imagine it is the thermal overload, but surely a E-Stop would be incorporated with the control circuitry.

Assuming it is NC and indeed a thermal protector then yes it can be incorporated into the control circuit.

Hi, my boss has been testing me and just has a motor he uses to get apprentices to build motor control circuits. Just built a DOL. And he wants to to do a star delta one now with an emergency stop. Just a little confused with some of the wiring along with the timer. My just written a list of what he wants in terms of switch over time, e.stop button connected through thermal OL etc but I have to draw up wiring diagram and put it into practice. Really enjoying the challenge and I know im still an apprentice but just some things are still confusing me. Thanks for the help though. Much appreciated

know im still an apprentice but just some things are still confusing me.

my apprentieship was in the 60's and things still confuse me. I'd not now be able to construct a star/delta starter as long as i coud fart.

Jordansheds88 said:

Hi, my boss has been testing me and just has a motor he uses to get apprentices to build motor control circuits. Just built a DOL. And he wants to to do a star delta one now with an emergency stop. Just a little confused with some of the wiring along with the timer. My just written a list of what he wants in terms of switch over time, e.stop button connected through thermal OL etc but I have to draw up wiring diagram and put it into practice. Really enjoying the challenge and I know im still an apprentice but just some things are still confusing me. Thanks for the help though. Much appreciated

Click to expand...

If you're on about connecting the thermal overload in the control circuit, just remember basics... 'stops in series, starts in parallel' and employ your t/o as a 'stop'.

Put your boss to task and ask him the safety system category level first as that denotes the design of the control system for the e-stop...

I wouldnt call that the thermal overload, I would thnk that is a thermistor which detects the internal temperature of the motor. The resistance between the connection changes with the temperature, its not open or closed. For this to stop the motor it would need to be connected to a specific relay for this job.
the thermal overload is usually in the panel next to or under the contactor for the motor. Or atleast that is the terms I use for the components
?

It could be either a thermistor (resistance varies smoothly with temp) or a thermal switch a.k.a protector or Klixon (trademark) that opens at a certain temp. In the latter case it can be incorporated as one of the stops in the control circuit. As @WallaceP points out, the term 'thermal overload (relay)' usually refers to the overcurrent sensing device within the starter. That is 'thermal' because it has heater elements that mimic the temperature rise of the motor, while the thermal switch actually detects the motor temperature itself. It's more accurate as a representation of the motor temp, but slower to act, so the overload relay in the starter is still needed.

@Darkwood makes a good point that unless you know what category of safety the control system is required to achieve, you can't say anything about what is or is not acceptable for an E-Stop. E.g. if it fails to stop, what is the result... danger to life? A flooded plant room? etc.

So, we're all just guessing, again.

Oh well, think I'd better stop trying to make things basic and, maybe, helpful to understand for learners. ?