3ph motor starter - automatic restart

[shespuzzling]

Hi,
Trying to understand figure out how to prevent automatic restarting in a 3 phase motor starter with hand/auto/off positions. Based on the wiring diagrams I've seen, the motor will automatically restart if you're in auto. Is this true and what would that control circuit look like if it had drop-out protection?
Thanks.

 

[ActionDave]

Restarting after what? An overload or stop signal in the control system?

 

[retirede]

And what is in the “Auto” circuit?

 

[LarryFine]

Based on the wiring diagrams I've seen, the motor will automatically restart if you're in auto.

Normally, a standard motor controller may start the motor when in 'hand', but not in 'auto'.

A simple self-latching relay (same as a 2-button starter) can prevent any auto re-starting.

 

[shespuzzling]

Thanks, let me try to clarify. I've attached the wiring diagram I was referencing. This diagram doesn't show the momentary start/stop for the hand position but I'm assuming that's present also

When you're in auto, and the "operating control device" relay is controlling the starter circuit, if you lose line voltage power to your motor for whatever reason, the "operating control device" would stay closed and then when power came back to your motor, the motor would automatically restart. What protections could be in place to prevent the motor from automatically restarting?

 

[retirede]

We used to accomplish this with a conventional 3-wire circuit (start/stop momentary push buttons) that controlled a relay. The relay contact is then wired in series with the H-O-A switch.

After a power interruption, the user must press the start button and seal in the relay in order to restart.

 

[LarryFine]

What protections could be in place to prevent the motor from automatically restarting?

What I described: a simple additional latching relay that you have to push a button to engage. It can even be powered by the same control transformer. Click to enlarge:



Ignore terminal numbers; they indicate 12v relay terminals.

 

[Frank DuVal]

Schematic looks right for most applications. There is no Start Stop buttons in HAND because you have to move the selector switch to HAND to run the motor manually. This is the Start Stop function of your hand. To turn off the motor manually, simply use your hand to turn the selector switch to OFF.

Yes, as wired the external control circuit asks for the motor to run when the selector switch is in AUTO position. If power goes off and comes back on, the motor will run when the control circuit asks for it to run.

If you need to make sure the motor does not run after power is applied (even if the control circuit wants it to) until human intervention lets it run, you need to add a standard Stop Start circuit after the fuse in the diagram. The one would need to press START after every power failure, even if in HAND, OFF or AUTO selector switch position.

You need two push buttons and a control voltage SPST relay.

Remove wire from fuse that goes to control circuit. Then wire fuse to N.C. push button to N.O. pushbutton with relay contact in parallel to N.O. contact this then connects to wire removed from fuse and the relay coil. Other relay coil wire to other terminal of transformer.

Larry beat me to it....

 

[Besoeker]

Thanks, let me try to clarify. I've attached the wiring diagram I was referencing. This diagram doesn't show the momentary start/stop for the hand position but I'm assuming that's present also

When you're in auto, and the "operating control device" relay is controlling the starter circuit, if you lose line voltage power to your motor for whatever reason, the "operating control device" would stay closed and then when power came back to your motor, the motor would automatically restart. What protections could be in place to prevent the motor from automatically restarting? View attachment 21853

A couple or three points.
I agree. No start /stop shown in hand control. To that extent at least, the drawing is surely incomplete?

Are there really three overload contacts? All the three-phase overloads I've seen have just one NC contact?

Are the overloads self resetting?

 

[LarryFine]

You need two push buttons and a control voltage SPST relay.

Remove wire from fuse that goes to control circuit. Then wire fuse to N.C. push button to N.O. pushbutton with relay contact in parallel to N.O. contact this then connects to wire removed from fuse and the relay coil. Other relay coil wire to other terminal of transformer.

Larry beat me to it....

I'm suggesting he doesn't need the N.C. button.

 

[don_resqcapt19]

A couple or three points.
I agree. No start /stop shown in hand control. To that extent at least, the drawing is surely incomplete?

Very common for the HOA to directly run the motor in the hand position without any other controls.

Are there really three overload contacts? All the three-phase overloads I've seen have just one NC contact?

Often seen it drawn that way because many years ago there were three separate overload relay contacts that were wired in series. Not really the case anymore, but old habits die hard

Are the overloads self resetting?

Good question.

 

[Jraef]

It's not at all uncommon to not have a Start-Stop PB in an HOA "Hand" circuit, especially if the "Hand" operation is something only done for testing / setup when an operator is right there in front of it.

As to "automatically" restarting when in the Auto position, that is a function of whatever your automatic control system is. If that run command is coming from a PLC for example, and you don't want the unit to re-start after a power failure, then you build that into the logic of that PLC. If it's not a PLC, it can still be accomplished in whatever control system that is, you would need to understand that external control system better.

 

[Besoeker]

Very common for the HOA to directly run the motor in the hand position without any other controls.

Thank you for your polite response.
It would be interesting to know what the application is. If three phase, one would guess industrial. We wouldn't have got by without at least an external lock off EM stop.
Different strokes etc.

Often seen it drawn that way because many years ago there were three separate overload relay contacts that were wired in series. Not really the case anymore, but old habits die hard

Well, OK. But I've never seen it done that way and I was around before the Dead Sea reported in sick.....

 

[don_resqcapt19]

Thank you for your polite response.
It would be interesting to know what the application is. If three phase, one would guess industrial. We wouldn't have got by without at least an external lock off EM stop.
Different strokes etc. ....

Actually the hand position, at some of the industrial facilities, I work in bypasses all interlocks with the exception of the overload really contact. It is used in a try-lock-try lockout verification for mechanical work on the equipment. You go to the HOA at the motor and "try" the motor in hand, go to the MCC and lockout the starter, and then return to the HOA and "try" the motor again. If the motor turned on the first try, but not on the second try, you are pretty sure you have locked out the correct starter. If any of the interlocks were in the hand circuit, you could not be as sure. For this application the "hand" position of the HOA is spring return to center, so you can't run the equipment in hand.

 

[ptonsparky]

Well, OK. But I've never seen it done that way and I was around before the Dead Sea reported in sick.....

Wow, that’s old. I must be older.

ABs were that way. I’ve replaced or cleaned quite a few of them. CH, I believe. IDR the others.

eta: SQD

 

[petersonra]

Normally in auto mode you want it to start automatically so I don't see the problem.

 

[Besoeker]

Normally in auto mode you want it to start automatically so I don't see the problem.

Well, I wondered about that. But the impression I got, rightly or wrongly, it is that it is being seen as a problem by the OP. That's what prompted me to ask if the overloads were auto reset. I've seen some that can be switched between auto and manual reset.