Servicing an old electrical motor

Hello,

I am servicing an old electrical engine. There is a red and a yellow wire (which were connected to phase and neutral and the motor was working that way).

After opening the motor I found a third wire which is black and connects to this part that I am holding in my hand. What is it? Could it be the ground wire?

The grey part is pushed down when the axis of the motor is in place and all screws are in place, which lets current flow to the tip of the black wire, whereas as it is now, the grey part is pushed up by the yellowish part which acts as a spring, disconnecting the tip of the black wire.

If that's not the ground wire, maybe I could wire a ground cable to one of the screw hole in the outside shell of the motor?

Thanks for your help!

A_Union_of_Kobolds 2 points 2 months ago

I would think thats the equipment ground but I dont know why it would be positioned to carry current normally as youve described, how old is the engine? Where does the black wire go from there?

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pitajellybug 2 points 2 months ago

The engine llooks old, a couple decades old I would say. The label on it says "A.L. CLARET, type MK 238". I did a continuity test from the black wire to the outer shell and it didn't beep. The black wire seems to go into the coil.

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A_Union_of_Kobolds 2 points 2 months ago

Probably another hot leg then, which would make sense...

Idk, im an electrician but I dont know much about engines. Sorry, hopefully someone with more experience can chime in.

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pitajellybug 2 points 2 months ago

Hot leg as in a wire with current?

I got an idea. When the engine stops, I hear a metal noise. Maybe the grey part stops being pushed when the engine stops. So maybe that is a return wire which is supposed to turn on a light that shows that the engine is running.

There might be no ground connector on this engine. The copper coil seems to be insulated. I get no continuity when I touch the copper coil and it doesn't feel cold when I touch it with my hand. I'll just screw a ground wire to the outside shell of the engine.

Thanks for your help :)

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A_Union_of_Kobolds 1 point 2 months ago

Hot leg as in a wire with current?

Yeah, thats what I was thinking. Like on a 240v circuit (dryer, oven, anything with a strong load in a home), youd have two hot wires. Each on their own supplies 120v but together you get 240v. (In the US obviously, British systems run 240v on each hot i believe)

I like your theory about that being a signal wire going to a run light though, that seems sensible. From what it sounds like that seems like a strong possibility.

Dedicated ground wires weren't common until a few decades ago in homes (the neutral/return wire is bonded to ground so that was "good enough" until enough homes burned down). My (extremely limited) understanding of automotive electricity is that it went the other way in vehicles, you have a hot wire and a chassis ground going to everything until recently as more electronics were added and a dedicated neutral was necessary.

I'll just screw a ground wire to the outside shell of the engine

That should be good enough id think

Let me know how it goes!

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A_Union_of_Kobolds 1 point 2 months ago

Out of curiosity, what did the engine come out of?

One of my friends is an automotive EE, hes currently (heh) agreeing with the chassis ground theory but hes seen weird shit like this before on military hardware

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