Motor wiring diagram

wirebender · Jul 11, 2012

I have a 3HP 3phase 230/460V motor for a through the wall exhaust fan.
The wiring diagram shows 2 red wires labeled t-stat.
Under the diagram it says "Use a manual momentary start switch only".
I've not seen this before and am unsure what to do.
Does that mean it can't be line started?

wirebender · Jul 11, 2012

Here's the nameplate.

don_resqcapt19 · Jul 11, 2012

The "J" leads are usually internal thermostat leads used to shut down the motor on high winding temperature. I am not sure about the "manual momentary start" comment. I think they are looking for a motor starter with a three wire start stop circuit. The "J" leads would be connected to the control circuit to drop the starter out on high temperature. The word "manual" in that comment does not make a lot of sense to me.

dkailiuli · Jul 11, 2012

I'm guessing they want a momentary push button so that in the event the motor windings get hot enought to trip your control circuit, it can't be automatically started again and damage or further damage the motor. It would take you pushing the momentary push button to start it again.

wirebender · Jul 12, 2012

dkailiuli said:
I'm guessing they want a momentary push button so that in the event the motor windings get hot enought to trip your control circuit, it can't be automatically started again and damage or further damage the motor. It would take you pushing the momentary push button to start it again.

Ah, that makes sense. Can anyone verify?

Jraef · Jul 12, 2012

Yes, that's exactly what it means. What they are saying is that this is an internally protected 3 phase motor, something not common in industry, and it therefore does not require an external overload relay be used with a contactor (or manual motor starter) that will not automatically reset. Or put another way, you could theoretically use this with just a 3 pole contactor operated by a selector switch or toggle switch with the t-stat in series with the coil, not a full blown motor starter. But if you do, the control switch remains closed so the t-stat will cool down and allow automatic restarting too soon and apparently this motor is not rated for that. Somewhat common in motors designed for specific applications, like OEM vent fans for example. If you notice, this motor is not UL listed, it is a UL Recognized component, which means whomever uses it must get the ENTIRE machine and control system listed after assembly, and that control requirement will need to be part of the scheme.

don_resqcapt19 · Jul 12, 2012

Jeff,
So in this case "manual" means a non-automatic restart of the motor?

Jraef · Jul 12, 2012

don_resqcapt19 said:
Jeff,
So in this case "manual" means a non-automatic restart of the motor?

Right. If it over heats, a human is required to intervene.*

* thereby accepting blame for the fire when he ignores common sense and resets it anyway. :jawdrop:

Jraef · Jul 12, 2012

wirebender · Jul 12, 2012

Okay, so the only thing the plans call for on my part is a disconnect.

There was nothing in the instructions about doing anything with the t-stat wires, so I believe my responsibility ends with wiring the motor from the disco.

Is there anything wrong with just starting the motor with the disco?

This is in an auto shop and I don't think a restart button at the disco would be a wise choice. The mechanics would just hit the reset and never say anything to anyone. It would be better if it takes some effort to restart.

Smart $ · Jul 12, 2012

wirebender said:
Okay, so the only thing the plans call for on my part is a disconnect.

There was nothing in the instructions about doing anything with the t-stat wires, so I believe my responsibility ends with wiring the motor from the disco.

Is there anything wrong with just starting the motor with the disco?

This is in an auto shop and I don't think a restart button at the disco would be a wise choice. The mechanics would just hit the reset and never say anything to anyone. It would be better if it takes some effort to restart.

I don't believe the NEC requires the T-stat to be connected, but the motor is required to have overload protection in some manner.

Starting such a motor with a disconnect is not the norm. How is the overload protection supposed to flip the handle? :roll:

Is there a motor controller (starter) somewhere in the scheme of things?

hurk27 · Jul 13, 2012

Smart $ said:
I don't believe the NEC requires the T-stat to be connected, but the motor is required to have overload protection in some manner.

Starting such a motor with a disconnect is not the norm. How is the overload protection supposed to flip the handle? :roll:

Is there a motor controller (starter) somewhere in the scheme of things?

I think this is one case where a shunt trip could be utilized?

hurk27 · Jul 13, 2012

Wait I think the contacts of this internal thermo would be NC and open on high temp, so yes you would need to use a contactor that would shut down, a start stop circuit would require a manual restart and if you use a button labeled "RESET" instead of start might make them think before restarting it.

I would not wire this motor without the high temp wired in.

wirebender · Jul 13, 2012

Smart $ said:
I don't believe the NEC requires the T-stat to be connected, but the motor is required to have overload protection in some manner.

Starting such a motor with a disconnect is not the norm. How is the overload protection supposed to flip the handle? :roll:

Is there a motor controller (starter) somewhere in the scheme of things?

No, no starter.

E plans show disco.

Instructions with the fan do not show how to wire.

Only wiring diagram is what i posted.

I am not a motor man, and without a diagram or instructions, I am lost.

Thanks for your help.

Smart $ · Jul 13, 2012

wirebender said:
No, no starter.

E plans show disco.

Instructions with the fan do not show how to wire.

Only wiring diagram is what i posted.

I am not a motor man, and without a diagram or instructions, I am lost.

Thanks for your help.

Could be a combination starter disconnect.

Example, not a recommendation or endorsement: http://literature.rockwellautomation.com/idc/groups/literature/documents/pp/512-pp002_-en-p.pdf

Jraef · Jul 14, 2012

wirebender said:
Okay, so the only thing the plans call for on my part is a disconnect.

There was nothing in the instructions about doing anything with the t-stat wires, so I believe my responsibility ends with wiring the motor from the disco.

Is there anything wrong with just starting the motor with the disco?

This is in an auto shop and I don't think a restart button at the disco would be a wise choice. The mechanics would just hit the reset and never say anything to anyone. It would be better if it takes some effort to restart.

No I think you are misinterpreting. You are responsible for a proper circuit for this motor in accordance with article 430 of the NEC. As PART of that circuit, the running overload thermal sensor for the motor is built in, but you are STILL responsible for for making it work. It's only a sensor, you have to run that t-stat circuit into something that kills power to the motor circuit, like a contactor. All that notice meant was that the OTHER controls for that contactor must not be a maintained circuit, it must be momentary so that it drops out when tripped and must be reset by a person.

Or you could use a regular motor starter as well.

wirebender · Jul 14, 2012

Okay, thanks, everyone, I'll get the ball rolling on getting some kind of controller.

Motor wiring diagram

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