Sanity Check - Motor Voltage Wiring

will.mcray

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I have 1940 Monarch lathe with original motor. This is a dual voltage motor with 9 leads. Contractor panel says 480V. Today I pulled the motor wiring cover off and its obvious someone has been in it one upon a time. Electrical tape wrapped everything. Looking at the wiring, the numbers on the leads are no longer visible as expected, but one can have dreams right... Tracing the leads, all 9 are used, three from the motor to a L lead. This indicates to me this is wired for low voltage already. Otherwise I should see six pairs of connections for high voltage. See photos. What do you all think?
Wiring Data Plate 2.jpg

Motor Wiring.jpg
 
I have 1940 Monarch lathe with original motor. This is a dual voltage motor with 9 leads.

Sure look like its connected for low voltage to me. Threw me for a loop for a minute, since this isn't the "normal" 9-wire dual-voltage configuration. The normal is a wye connected motor, and the low voltage has each incoming line going to two wires, with the remaining three tied only to each other.

This one has line going to three terminals each. I scratched my head for a while and sketched on a napkin, and realized that this motor is delta connected. But the connections all make sense.

What are you trying to do? Do you want to run it on low voltage or high?

Regarding the cabinet, never trust a label that says "wired for xxx volts". When I bought my bridgeport, the motor said "wired for 480V", but the twist-lock plug was for 240. I got suspicious and opened up the junction box, and sure enough, someone had reconnected it for 240V. There was also a small transformer to power the DRO and power feed, and checking its primary wiring confirmed that it too was wired for 240V.

I suggest checking everything you can in the control cabinet for clues. Contactor coil labels, if the contactors run directly from the line. Control transformer primary taps and wiring. There are probably other clues as well.
 
I wanted to rewire it for 220v because I was told by the seller it was wired for 440v but he had no clue about the motor nor did he know it was a dual voltage motor. He picked this up through an auction. He just went off what was on the contractor cover. As you pointed out, I wanted to verify the connections which I raised an eyebrow when I saw electrical tape on there. The seller never ran it either. So it collected dust for a long time until he got tired of walking around it. Thanks for the reply.


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Last edited:
Put power to the lathe today (220v 3ph) to the lathe and motor spins nice, smooth and quiet! All RPM ranges work. The feeds in both directions works and reversing the motor. The lead screw and half nuts work great as well. I am happy thus far and this 80 year old lathe have a breath of new life!


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