[PTMINC]

Hi, I am getting a new to me ML-20 Monday. My concern is preparing a proper ground for the machine. This is the existing set-up I have:

My shop is next door to the main shop where the 3 phase power comes in.
From that point the power comes under ground and up into the service box in my shop. There is an existing run of 3 wires (no ground wire) to the spot I want to set the machine.
The landlord says the previous machine that ran there was a large surface grinder that used the conduit as a ground. (I've read enough on here to know thats not a good idea.)
The building has a ground rod in the front left of the building with a wire that runs across the top of the building to another ground rod in the right rear of the building and along that wire span
on top of the building are 3 equally spaced small rods going up from the wire. I assume for lightning protection. The landlord says it was that way when he bought the place.
Any suggestions would be greatly appreciated.

Thanks,
Scott

[quantummachine]

do not compromise on power supply, get a solid, well capacity 3 phase power cord to your machine.

[Al_The_Man]

It is permissible for certain conduits and fittings to act as grounding conductors, preferably I like to run a separate GND conductor also.
What jurisdiction are you in?
Al.

[PTMINC]

I'm really not sure about the conduit reg. I'm not really comfortable with it. I could run a conductor back to the box, or a ground rod. However I've read some of the literature you have posted on here so I'm not sure I'm comfortable with that either.
Honestly I'm not sure what to do...All the stuff about frame grounding and such. I'm used to having the green wire to hook up and forget about it with all my manual machines. I didn't want to make another conduit run just for the ground wire
but I will if thats my best option.

[PTMINC]

I was just thinking I could pull the existing wire, (it appears to be #6) and pull 4 wires back through. It would probably have to be #8 wires.

[PTMINC]

do not compromise on power supply, get a solid, well capacity 3 phase power cord to your machine.

I want to do it right, what do you think of just pulling new #8 wire back through my conduit run?

[PTMINC]

It is permissible for certain conduits and fittings to act as grounding conductors, preferably I like to run a separate GND conductor also.
What jurisdiction are you in?
Al.

I am in West Tennessee. Zip code 38355

[allen mullis]

Don't get crazy with it, it is 3 phase and should be balanced. If you want to do the absolute best thing, drill a hole in the concrete beside the machine, drive a 6' ground rod and give that machine its own dedicated ground. Be sure that if you do this, that there is no other potential ground, like the metal conduit. If there is, and there happens to be a ground fault on another machine somewhere and the resistance is less on your lathe, it could go through the frame to get to ground. Not likely to hurt the lathe, but anything is possible with electricity. The benefit of doing it this way is isolation. Any stray voltage has a straight path to earth ground, without having to depend on ground lugs in a panel or screws at conduit joints. It should help eliminate any possibilities of electrical noise as well, although there should be a filter in the electrical cabinet that feeds the control as well as the computer power supply that further eliminates that possibility.

I want to do it right, what do you think of just pulling new #8 wire back through my conduit run?

[mactec54]

I am in West Tennessee. Zip code 38355

Yes pull a new Ground wire, in from the main power supply, it seems they may have all the Ground rods bonded, which is the correct way for it to be done, so if they are all bonded, then you could use a ground wire from any of the ground rods they have around the building, it is always safer though, to bring your Ground from where your power supply is coming from, as for the conduit, if it was new it may be ok, but is it worth it, pull in a Ground then you will have peace of mind

[mactec54]

Don't get crazy with it, it is 3 phase and should be balanced. If you want to do the absolute best thing, drill a hole in the concrete beside the machine, drive a 6' ground rod and give that machine its own dedicated ground. Be sure that if you do this, that there is no other potential ground, like the metal conduit. If there is, and there happens to be a ground fault on another machine somewhere and the resistance is less on your lathe, it could go through the frame to get to ground. Not likely to hurt the lathe, but anything is possible with electricity. The benefit of doing it this way is isolation. Any stray voltage has a straight path to earth ground, without having to depend on ground lugs in a panel or screws at conduit joints. It should help eliminate any possibilities of electrical noise as well, although there should be a filter in the electrical cabinet that feeds the control as well as the computer power supply that further eliminates that possibility.

What you are suggesting is not legal, ( Code Violation) if a separate Ground rod is used it must be Bonded to all other Ground Rods that are in use around the building

[PTMINC]

Yes pull a new Ground wire, in from the main power supply, it seems they may have all the Ground rods bonded, which is the correct way for it to be done, so if they are all bonded, then you could use a ground wire from any of the ground rods they have around the building, it is always safer though, to bring your Ground from where your power supply is coming from, as for the conduit, if it was new it may be ok, but is it worth it, pull in a Ground then you will have peace of mind

I agree, not worth it. I'm going to pull the new wire from the service box.

Thanks,
Scott