10" GMF Grinder NOS Wiring Issue

[colmkarter]

Hello from Canada! This is my 1st post on WWF.

Recently I acquired a NOS 10" GMF Grinder and pedestal to suit. It had been owned by an elderly farmer and evidently has never been wired up. So the stones are brand new. It is a 240v 3 phase unit (at my shop 1 hour west of Toronto) and I need assistance to it wire up. Weighs about 100lbs and looks similar to the 8" GMF pictured in the older threads.

Absolutely a qualified electrician will reveiw matters beforehand as I am duly cautioned by the other threads on GMF and matters electrical. Power can kill and I'm not wishing to go there.

There are 2 wheels and a central 2 position switch which I believe controld each wheel individually. Underneath 3 wires come out from the grinder...ALL YELLOW. They are connected to a small white ceramic block and thence to the switch and the motor or 'cap'.

From that terminal block there are 3 cloth covered wires going to the functions of the grinder. Q: should these older style wires be replaced/ they appear in good condition.

How to determine which of the 3 yellow wires are to be connected? Should the plug be a 3 pole 4 wire or a 2 pole 3 wire piece. My shop has 240 outlets that were set up and used for a 240v welder. They are 3 prong style...one U shaped and 2 flat vertical prongs.

What cable wire to use...10-3 seems the likely choice?

And finally how much is this grinder worth...it will certainly outlast me!

Should I exchange one wheel for a 12' buffing wheel will any imbalance problems arise?

Thanks in advance.

Colm

All assistance appreciated.

[colmkarter]

Anyone downunder? My question is buried....what to do now?

[Chas]

Hello Colm,

It is difficult to believe you have a grinder which can control the wheels individually. If the grinder is truely three phase, I would not expect a "cap" to be included in the circuitry. The usual connections for a three phase machine would be to connect a phase to each of the terminal block connections, plus an earth wire to the machine frame. You would thus need a four wire cable with the appropriate 3 phase + E plug. You don't state the motor current, so it is difficult to advise on cable size. Two of the cable connections will need to be swapped at the terminal block if the grinder rotates backwards.

On re-reading your post, I am not clear whether the terminal block is the connection point for the power, or is an internal wiring connection. Perhaps you could provide a picture or diagram? Whatever the arrangement, the power should connect to the switch first,

A buffing wheel is lighter than a grinding wheel and I would not expect a problem.

Regards,
Chas.

[gerhard]

Hi Colm,

i totally agree with Chas, all the important things are in his reaction already. Some pictures would be helpful, including one from the switch setup and from the machine's type plate.

Cloth type wire insulation need not be bad; it is common for induction motor stator packs to be fitted with these. The cloth hose is impregnated with an insulating water resistant varnish, so such wires are perfectly okay unless the insulation is damaged or visibly deteriorated in any way.

I concur with Chas about both wheels/discs having separate ways of control or different drive systems. I've never seen this incorporated in one single machine, unless it is a very large unit comprising several functions, like those in shoe repair shops.

A plug with three prongs would suggest one for earth/ground, one for live wire and one for neutral/return, boiling down to single phase. Three phase plugs have four or five prongs ( 3x phase, 1x earth and 1x neutral in case of a fifth prong).

You mentioned three wires of the same colour, which sound like the motor's stator pack wires. If such motor leads all have the same colour, the motor is usually wound in three sets of coils, in fact exactly like three phase motors are. But that doesn't necessarily mean that it needs three phase power to run. A "three phase wound" motor combined with a starting/running capacitor is known as the "Steinmetz method", but that is typically used for applications where motors need to run both forward and reverse (industrial washing machines etc.). This is not the case for a grinder and these tend to have thicker gauge main coil windings and thinner gauge auxiliary wining in single phase cases, but your machine could be a rare example of a Steinmetz array in a grinder nonetheless.

And you mentioned a two setting switch. Would that be zero/one (off/on) or zero/one/two (off/low speed/high speed)? In the latter case you have a 4-pole/2-pole stator setting for 1500/3000 rpm at 50 Hz or 1800/3600 rpm at 60 Hz. If this is so, the stator is not a three phase wound Steinmetz type unless there would at least be six wires coming from the motor, with two sets of three having different colors to keep the pole arrays from getting mixed up.

Anticipate to hear from you again

till then, kind regards

gerhard