Help wire a 3-phase motor

Cannonmn · Jul 24, 2017

I have a 3-phase pedestal grinder missing all tags, no id's at all. It may be a Queen City grinder but who knows or cares now. Seller said it would run on 220v but would run better on 480v, whatever that means. The wires on the power cord presently are color-coded for 208/3 phase, but from what he said, that doesn't mean much. I have yet to open the AB box and the Motor's wire box to see if I can tell from them. If not, I'll be looking for a way to tell how to wire it using an ohm meter, since I was told that can be done and you folks can give me instructions.

JST · Jul 24, 2017

You go ahead and have a look, THEN ask.

Right now you are not really asking a question....

Do you want to run this on "220V"? If so, you have 3 wires, and so does the 3 phase, what's the issue? If it spins the wrong way, reverse 2 of the 3.

johansen · Jul 25, 2017

if its a 480v motor it will be useable on 240, with a fourth of the hp and torque..

JST · Jul 25, 2017

johansen said:
if its a 480v motor it will be useable on 240, with a fourth of the hp and torque..

Which is why it's safe to just hook it up on "220V" without sweating the voltage. That's why I asked.... seems like he was asking about ways to get 480V and might have .wanted to run it on 480.

6PTsocket · Jul 25, 2017

johansen said:
if its a 480v motor it will be useable on 240, with a fourth of the hp and torque..

Running a motor at significantly lower voltage than it is set up for causes it to draw excessive current, run very hot and evenually do damage or trip the breaker. This same thing happens when people run a long undersized extension cord but not nearly as badly as what you suggest.

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Yan Wo · Jul 25, 2017

6PTsocket said:
Running a motor at significantly lower voltage than it is set up for causes it to draw excessive current, run very hot and evenually do damage or trip the breaker. This same thing happens when people run a long undersized extension cord but not nearly as badly as what you suggest.

With respect, I question your conclusion. If correct, then running a motor at zero voltage would cause it to draw infinite current.

Gorgoth209 · Jul 25, 2017

Take a photo of the unit nameplate, take a look under the cover, and take a photo close up of the leads on the end so we know what we are working with.
Thanks

Jraef · Jul 25, 2017

6PTsocket said:
Running a motor at significantly lower voltage than it is set up for causes it to draw excessive current, run very hot and evenually do damage or trip the breaker. This same thing happens when people run a long undersized extension cord but not nearly as badly as what you suggest.

Sent from my SM-G900V using Tapatalk

+1

Yan Wo said:
With respect, I question your conclusion. If correct, then running a motor at zero voltage would cause it it draw infinite current.

That's a bit hyperbolic.

He's correct, running a motor at other than its rated voltage will result in poor performance at BEST, but more importantly, possible dangerous conditions. A motor is a "dumb animal" in that it will ATTEMPT to run at it's rated speed, even if it can't. So in that attempt, it will continue to draw more current as the slip increases, but because of the lack of torque due to the incorrect voltage, that slip will NEVER decrease because it will never get to its rated speed without rated torque, unless there is almost ZERO load on it. The grinder would keep drawing high current until the wires catch fire.

So back on track with the original issue; IF that motor is designed for 440V, the conductors in that cord are likely selected based upon that current draw. If you simply connect it to 220V, the current could be 2x what those wires are rated for, we just don't know.

You need the nameplate information. Guessing is dangerous.

JST · Jul 25, 2017

6PTsocket said:
Running a motor at significantly lower voltage than it is set up for causes it to draw excessive current, run very hot and evenually do damage or trip the breaker. This same thing happens when people run a long undersized extension cord but not nearly as badly as what you suggest.

Sent from my SM-G900V using Tapatalk

So far he is not even running it under load. Spinning it at no load will NOT draw too much current unless something ELSE is way wrong. It at least tests the machine.

Also, if he stays within the actual power it has wired 440 and running 220, it would be OK, although I would rewire it to be correct ASAP, myself. Overloading in ANY situation draws excess current and risks overheating motors.

6PTsocket · Jul 26, 2017

Yan Wo said:
With respect, I question your conclusion. If correct, then running a motor at zero voltage would cause it to draw infinite current.

I think you should experiment and plug your 220 devices into 120 and tell us how it worked out.

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Illinoyance · Jul 26, 2017

Is the A/B box a magnetic starter? If so its coil voltage would give you a clue.

Yan Wo · Jul 27, 2017

6PTsocket said:
I think you should experiment and plug your 220 devices into 120 and tell us how it worked out.

I see my attempt at humor has failed -- as usual. I shall defer to your expertise, and stand corrected.

Cannonmn · Jul 27, 2017

Gorgoth209 said:
Take a photo of the unit nameplate, take a look under the cover, and take a photo close up of the leads on the end so we know what we are working with.
Thanks

As mentioned this item has no nameplates anywhere. I'll post the photos requested below, with brief comments. The Motor has 9 original black wires going a couple of feet down into the pedestal. Here's decal inside AB box.

Cannonmn · Jul 27, 2017

Motor lifted off pedestal showing 9 wires.

Cannonmn · Jul 27, 2017

Wires enter through opening in Motor casing. I didn't see any way to get into the Motor near the wires.

Cannonmn · Jul 27, 2017

Power enters pedestal from AB box here. I pulled wires out until the connections to the labeled black wires (T1, T2, T3) were visible.

mike_kilroy · Jul 27, 2017

Yan Wo said:
With respect, I question your conclusion. If correct, then running a motor at zero voltage would cause it to draw infinite current.

Cute reply. Too bad an induction motor is not a linear device Wo.

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SAF · Jul 28, 2017

Cannonmn,

From what you posted, it appears that your grinder is a 2HP 3Φ 220/440 Motor.

Currently setup for 440V operation.

Clues of how to tell:

The manual motor starter is rated for 2HP max @ 220V or 440V, on the label

The Existing N19 Heater elements are rated at 3.26A

The NEC full load current for a 2HP motor is 220/440V 6.8/3.4A

To operate that motor at 208V will require 7.5A and heater size N28 (good for 7.63A)

To change the motor winding connections for low voltage operation (220), Reattach the grinder to the pedestal.
Lay the unit down, and reconnect the 9 motor leads inside the pedestal, to match the diagram for low voltage.
The 9 leads are spliced to the 3 leads, L1,L2.L3 entering the manual starter.
DO NOT operate the motor with the current heaters installed, even momentarily. Doing so will damage the heater elements in short order. And worse it will overheat the heater relays and cause them to be uncalibrated or fail to function properly. That's an old manual starter, but heavy duty. If you get the correct heaters for your voltage, it will likely last as long as you.

SAF Ω

*Jaref ought to be along shortly to tell you to junk that old starter, and put something more modern on there that is supported and compliant with today's standards (one with 3 overload relays). But I think it goes with the grinder well. Worked for the last 70+ years, why change now? Personally, I'd rather invest for some grease in the dried out bearings, rather than a new controller.

Cannonmn · Jul 28, 2017

Thanks, one question so far:

"Lay the unit down, and reconnect the 9 motor leads inside the pedestal, to match the diagram for low voltage."

I haven't found a diagram for this motor. I don't know if lead-numbering was standardized at all. I have the lead connection map for low and high-voltage use from my 3/4 hp., 1950's 9-wire Doerr Motor, but no idea if that's useful here or not.

Cannonmn · Jul 28, 2017

Thanks, couple of question so far:

"Lay the unit down, and reconnect the 9 motor leads inside the pedestal, to match the diagram for low voltage."

I haven't found a diagram for this motor. I don't know if lead-numbering was standardized at all. I have the lead connection map for low and high-voltage use from my 3/4 hp., 1950's 9-wire Doerr Motor, but no idea if that's useful here or not.

Since it appears to be wired for high-voltage now, wouldn't it be wise to wait a bit until I have 480volts Available, then test-run it on 480/3 phase? If it worked that way I'd have no reason to rewire it. Our use for that huge grinder is limited, maybe 1 hour/week.

Help wire a 3-phase motor

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