Question about grounding a DC motor

[Chris Turner]

So, I just picked up a nice little DC motor with variable speed control.

I plan on basing a new winder around this, but since I plan on making the platform for the winder out of wood, and the motor needs to be grounded, would it be enough to attach the 2 ground wires coming out of the speed control box (one from the plug and another from the motor) to the shaft I'm also using on the winder, found here: Portable Shaft? I'm thinking that it's not, since the shaft itself is not connected to any sort of ground. If not, then how would I go about properly grounding, or earthing, this thing?

I'm no electrician, so I'd like to not kill myself if possible.

Or do I need to rethink this and use a different type of motor?

[Magnut]

First off, good choice on using a DC motor. These are much easier to adapt. So what type of power supply are you using? What voltage is your motor? Is it simply a 110v ac supply rectified then to a controller? (or other way around 110v ac to controller then rectified) If you are talking about using the ground from the 110v ac cord then that would be fine to ground the motor with. In the end all potentials must be the same anyway to avoid shock. A ground is a ground is a ground. Don't mix that up with the grounded conductor which is the white or neutral wire. A small "bond" wire between all metal parts is a great way to reduce the hazards of electrical shock. Just be sure the electricity if shorted, has an easier path to ground than going through you.

The DC motor will have a lot more torque so be aware of pinch hazards. The DC torque can really hurt you if you get caught up. Not that I would know! 8^P
The link for your portable shaft did not work for me btw. If you can give specs to what your using for motor, power supply and controller it will be easier to help. It sounds like your on the right path though.

[Chris Turner]

This link should work for the portable shaft: H8024 1/2" Heavy-Duty Portable Shaft

Here's the motor I bought: DC Motor


The power supply is from the 110V wall socket, rectified through the variable speed controller I suppose. Here's a pic of the inside of the box, showing the 2 ground wires they say must be grounded to a machine frame:


If a ground is a ground is a ground, would it be safe to just connect those two green wires together? Since one comes from the AC plug, and the other goes to the motor itself...

[Magnut]

That seems like a good set up. Yes, you can connect those two grounds. Since you don't actually have a "machine", then connecting them will provide a ground for the case of the motor. I would maybe insulate them once connected before mounting the controller. Actually after looking at it in close up, I don't see where the case of the controller is grounded. Is it plastic or Anodized? If plastic, never mind. If Anodized... never mind. Anodizing provides some amount of insulation.

[Chris Turner]

The case seems to be plastic. So does that mean I can or can't connect the 2 ground wires together?

[Joe Gwinn]

The case seems to be plastic. So does that mean I can or can't connect the 2 ground wires together?

It has to have a way to ground the motor frame, if not the case. Look for a green wire or terminal screw.

One connects this green wire/screw to the green wire in the green ground in the house power system. The green ground is that of the round pin (versus the two flat blades) in the power cord.

The plate on the motor may tell where this is. Or, get the instructions from the manufacturer.

The reason to ground the motor frame is so if the winding shorts to the frame, the circuit breaker will blow, not the hapless user.

[Chris Turner]

Okay.

One of the green wires in the photo is coming from the AC power plug. I assume that goes the house's green ground.
The other green wire comes from the cord that goes to the motor.

Do I need to connect both of these green wires to somewhere on the metal case of the motor?

No instructions came with this motor at all, and there's no indication of who the manufacturer is. I guess I may end up having to contact the seller to see what he/she has to say.

[Jazz P Bass]

Use your multimeter & see if there is continuity from the green motor cord wire to the motor case. (probably is)
If so, then simply connect the power cord earth wire to it.
And isolate it so it cannot come in contact with anything in the controller.
Most likely this was meant to be installed on machinery of some sort.
By tying both connections to the equipment frame everything would be safely grounded.

[Chris Turner]

Use your multimeter & see if there is continuity from the green motor cord wire to the motor case. (probably is)
If so, then simply connect the power cord earth wire to it.
And isolate it so it cannot come in contact with anything in the controller.
Most likely this was meant to be installed on machinery of some sort.
By tying both connections to the equipment frame everything would be safely grounded.

Perfect. There is continuity, as you expected, so I'll just connect the 2 inside the box and heat shrink the bare metal in the connection.


Thanks everyone! I'll be sure to post pics of the machine when it's all done.