[dnutsch]

I have a PM-25 that I have added a CNC kit to. Over the steppers I screwed on some galvanized sheet metal as a cover (into the mount, not the motor). I was touching the sheet metal over one stepper while jogging the same stepper and received a fairly good shock. Now, there could be something wrong with the wiring, or maybe not. Regardless of that issue, What I did find was the ground pin of the power cord did not show continuity to any part of the machine except the electrical box. The neutral pin does show continuity. The whole machine should be connected to earth ground to prevent shock, correct? This machine has a ground connection to the electrical box. The painted electrical box is connected to the machine with what looks like plastic spacers. I don't think it is making a connection. I'm fairly certain I need to add more green wire to ground the rest of the machine. My other concern is whether this stepper is defective. Under what circumstances would the stepper produce a shock while being energized? Would this require a bare wire to be contacting the housing, or would the motor induce current in the surrounding, non-grounded sheet metal?

[dnutsch]

photos of said machine
http://www.precisionmatthews.com/shop/pm-25mv/

[john-100]

I would say yes , its the norm for Chinese electrical goods

Going by the photos in various Chinese 6040 router threads
earthing is an after thought at best as they work without an earth , don't they !!!

it would appear the routers normally have the mains earth to the control box fastened to a painted metal surface !!!

john

[Al_The_Man]

I agree with the comment on Chinese machines and their grounding, or Lack of!
Your service supply Earth wire should be connected to the enclosure and all metalic parts of the machine and motor frames etc should be bonded or connected to a central star point in the enclosure, AKA Equi-potential Bonding.
Al.

[mactec54]

I agree with the comment on Chinese machines and their grounding, or Lack of!
Your service supply Earth wire should be connected to the enclosure and all metalic parts of the machine and motor frames etc should be bonded or connected to a central star point in the enclosure, AKA Equi-potential Bonding.
Al.

This has nothing to do with it being a Chinese built machine

The cnc conversion was self grown, so it obvious that this install has not been wired correctly

[Al_The_Man]

This has nothing to do with it being a Chinese built machine

My comment was directed to John's post that made the point regarding Chinese machines, it may not be 100% applicable in this case, but I stand by my comments based on personal experience.
A.

[john-100]

the way I read the original post is the control box with the blue LCD display , as shown in the picture linked to , is part of the machine as supplied
and has continuity to the ground pin on the mains plug but there is no continuity between the box and the machine body

that is the kind of thing I have found in past when checking imported Chinese products when they stopped working

using one of the screws fixing a plastic mains inlet to a painted metal box without removing the paint where the earth wires eyelet touches is a common practice that is not good enough - all it takes is applying a bit of masking tape before painting the box

what we don't know is if the CNCKIT was ready to go and just needed bolting to the milling machine

John

[mactec54]

My comment was directed to John's post that made the point regarding Chinese machines, it may not be 100% applicable in this case, but I stand by my comments based on personal experience.
A.

These machines in General have never had a Grounding problem, they are imported and sold by many different distributors, and electrically comply, it's the self installed part that is normally the problem

[mactec54]

the way I read the original post is the control box with the blue LCD display , as shown in the picture linked to , is part of the machine as supplied
and has continuity to the ground pin on the mains plug but there is no continuity between the box and the machine body

that is the kind of thing I have found in past when checking imported Chinese products when they stopped working

using one of the screws fixing a plastic mains inlet to a painted metal box without removing the paint where the earth wires eyelet touches is a common practice that is not good enough - all it takes is applying a bit of masking tape before painting the box

what we don't know is if the CNCKIT was ready to go and just needed bolting to the milling machine

John

I would hope that his is not wired like this, as if so he would of been using 2 different power sources to supply his machine, which would cause what is happening He would of created a Ground loop

[Al_The_Man]

AGAIN, I am not necessarily including this particular machine in my comments, It was a general statement on the delivered condition of some machines of Chinese origin, where there is often a blatant disregard to regulations regarding electrical safety!
A.

[john-100]

Mactec54
true
but ground loops don't give you a shock

its the lack of continuity between machines supply cable earth and the machine body that needs fixing first then the CNCKIT earth wiring

John

[mactec54]

Mactec54
true
but ground loops don't give you a shock

its the lack of continuity between machines supply cable earth and the machine body that needs fixing first then the CNCKIT earth wiring

John

Correct, I'm sure there are more than one problem if this is happening, some photos would be more tell more than words in this case

[dnutsch]

The CNCKit is just aluminum motor mounts. I added 4 stepper motors each which have 4 wires. those are connected with 4 conductor shielded cable to a grounded metal box which contains the 4 stepper drivers and a 48V power supply. When the chassis was not grounded, jogging one of the steppers energized the chassis. Now, I opened the CNC's electrical box and found the green plug wire is screwed into a 5 place terminal block that is screwed to the side of the electrical box. There are no other ground wires. The ground pin and the electrical box did not show continuity, so I sandpapered the paint off and reconnected. I ran a wire from that exterior screw on the electrical box to an exterior screw on the cutter head. The whole chassis showed that it was grounded, but this caused the breaker to trip when turned on. So I think there must be a short either in the stepper cable or in the motor itself.

As for ground loops, the stepper shielding is only connected to ground on the control box side and not to the steppers.

[mactec54]

The CNCKit is just aluminum motor mounts. I added 4 stepper motors each which have 4 wires. those are connected with 4 conductor shielded cable to a grounded metal box which contains the 4 stepper drivers and a 48V power supply. When the chassis was not grounded, jogging one of the steppers energized the chassis. Now, I opened the CNC's electrical box and found the green plug wire is screwed into a 5 place terminal block that is screwed to the side of the electrical box. There are no other ground wires. The ground pin and the electrical box did not show continuity, so I sandpapered the paint off and reconnected. I ran a wire from that exterior screw on the electrical box to an exterior screw on the cutter head. The whole chassis showed that it was grounded, but this caused the breaker to trip when turned on. So I think there must be a short either in the stepper cable or in the motor itself.

As for ground loops, the stepper shielding is only connected to ground on the control box side and not to the steppers.

Photos of how you have done this, does sound like you have a short some were, is the spindle motor Grounded

[hackish]

I read this post and decided to check. My machine is properly grounded. Possibly it was an error in his build or a defect in the machine construction. I checked the spindle, column and table, finding 0.2-0.4 ohms on all.

[dnutsch]

I disconnected the steppers and put the control box back together. Everything works fine, so the problem is in the steppers, cabling, or stepper drive wiring.

However, the grounding was bad as delivered and I did get shocked by my stepper motors, so if you pick up a similar benchtop consider cracking the control box and sanding down the paint if the multimeter doesn't show the entire machine is grounded.

Below you can see how the ground wire is connected to the interior painted surface and the green external wire I added to ground the rest of the machine (may run it through the wiring conduit later).

[dnutsch]

I read this post and decided to check. My machine is properly grounded. Possibly it was an error in his build or a defect in the machine construction. I checked the spindle, column and table, finding 0.2-0.4 ohms on all.

Yeah, wonder if your control box has a painted interior. I am also wondering if maybe some wiring is missing in my PM. It seems odd to add a five hole block just to screw one wire to the control box case.

[mactec54]

Yeah, wonder if your control box has a painted interior. I am also wondering if maybe some wiring is missing in my PM. It seems odd to add a five hole block just to screw one wire to the control box case.

Your incoming Power supply Ground should be connected to the 5 Hole Ground Bus, plus the spindle motor Ground, Plus the Power Supply Ground, and any other Grounds that are in your system should all be connected at that point

It is not correct the way it is, adding the Ground wire to the spindle does not help anything, unless all the main Ground wires are connected to the main Ground 5 hole Bus

[dnutsch]

All the present grounds are connected to the 5 hole bus, which is to say only the earth ground from the power cable going back to the electrical panel is present. The spindle does not have any ground wires coming from it. It is a BLDC with three main conductors. Maybe it should have a dedicated earth ground to the motor case. I don't know. That's just how it arrived.

Adding the ground wire did do something. It converted a previously undiscovered short into tripping the GFCI wall outlet, which is the whole point of grounding the machine.

[mactec54]

All the present grounds are connected to the 5 hole bus, which is to say only the earth ground from the power cable going back to the electrical panel is present. The spindle does not have any ground wires coming from it. It is a BLDC with three main conductors. Maybe it should have a dedicated earth ground to the motor case. I don't know. That's just how it arrived.

Adding the ground wire did do something. It converted a previously undiscovered short into tripping the GFCI wall outlet, which is the whole point of grounding the machine.

Adding that Ground wire unless it goes to the main Ground Bus, it could make it even more dangerous than it was before

It does not matter what type of motor you have everything needs be Grounded to the 5 Hole Bus, it's not safe if it is not, you must have some kind of power supply, may be more than one that all need to be grounded to that point in the cabinet

This is not original that is why it is messed up