Wiring in a ground wire

[machinistnoob]

Hello everyone, hope you all are well.
Got a new machine the other day! When I was looking under her skirt I noticed there is no ground wire into the panel. Just the three phases coming from the junction box where the plug will be wired. Where/how would I add a ground to this panel? Let me know if you need better pictures and thanks in advance!
M. Noob

 

[whitmore]

The ground wire terminates (at least) in the square electrical box that transitions the
AC cord to the wall to the flexible tube into that main panel. All such boxes have a
ground attach point. The various heavy metal bits are all in contact with each other, one
trusts.

Nothing prevents you from using an available position or three in the main panel to distribute ground to other
devices (DRO, utility lamps, etc). Use green or green/yellow wire, if possible.

 

[machinistnoob]

I see. So, I can attach a ground straight to an empty terminal on the bar that the other leads go to?

 

[Pevehouse]

Love the machine. In the market for one myself but they are hard to come by down here in the south

 

[machinistnoob]

Love the machine. In the market for one myself but they are hard to come by down here in the south

Thank you. I am excited to play with it.

 

[machinistnoob]

The ground wire terminates (at least) in the square electrical box that transitions the
AC cord to the wall to the flexible tube into that main panel. All such boxes have a
ground attach point. The various heavy metal bits are all in contact with each other, one
trusts.

Nothing prevents you from using an available position or three in the main panel to distribute ground to other
devices (DRO, utility lamps, etc). Use green or green/yellow wire, if possible.

After looking again, the picture is misleading. In the picture, it appears that the leads come into the machine, from the conduit and to the bar you see at the bottom. That is not the case. The leads in, go to the switch on the top right of the picture. From there, power is distributed to the transformer and other components and then to the bar and from there to the motor. Does this change anything?

 

[Hawkeye]

Connect one lead of a DMM set on ohms to any bare metal on the body of the machine and the other lead to the ground socket of the nearest receptacle. If you get very low resistance, the machine is grounded. One of those mounting bolts toward the bottom of the control panel would be a good one to check.

 

[machinistnoob]

Connect one lead of a DMM set on ohms to any bare metal on the body of the machine and the other lead to the ground socket of the nearest receptacle. If you get very low resistance, the machine is grounded. One of those mounting bolts toward the bottom of the control panel would be a good one to check.

Thank you. Will do. And if I don't get very low resistance...?

 

[GeneT45]

I see. So, I can attach a ground straight to an empty terminal on the bar that the other leads go to?

No. In general you want to terminate the ground directly to the chassis as close as practicable to where the cord enters. A hole, or often a threaded stud, is sometimes provided for this. From there you can tie your ground into a terminal if you want to distribute it to other areas of the tool, but it must be tied to the chassis directly. (There are modern terminal blocks that I think are acceptable for both purposes, but those in your picture aren't them...) That said, be sure you're not distributing the ground where you really want a neutral.

If you don't have a low-impedence path to ground, you will have to trace the wire - probably starting where you attached the ground - and make sure you have removed insulative paint, etc. Best practice is to use a lug with a star washer. NFPA 79 (relevant electrical code if this were a commercial device) requires 0.1 ohm or less, IIRC. Your meter may not be that accurate, so don't stress about it too much, but if it's high single digits or more, you can probably do better.

GsT

 

[RJSakowski]

I would use the black stud in the upper right corner of the panel as a bonding point. Check the stud for good bonding to the machine frame with an ohmmeter as stated above. I would also replace the three conductor power cord with a four conductor cord and a four conductor plug. If power comes in through conduit, pull an extra conductor for ground.

Checking for continuity between the machine frame and a nearby socket ground can be misleading. If the machine is on damp or wet concrete, you could have a low resistance reading but the machine is not necessarily grounded. There should be a physical wire going from the machine frame to the mains ground terminal. I have seen older wiring where the conduit was used as a ground. This isn't a good practice as conduit connectors can shift slightly, making a high resistance connection.