Wiring in a ground wire

[whitmore]

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

Generally, you want every enclosure with AC power inside to pass a ground-bond test at current
levels high enough to blow a fuse, when certifying a design, unless 'double-insulated' rules are
used.

That doesn't mean ALL metal parts (handles, etc) need ground testing,
because the AC power is elsewhere. On occasion, even the rotors of motors
need grounding (because grounding the case grounds the stator, but the rotors
are not if the bearings aren't in close electrical contact) but that's an odd
application-dependent variation.

The case of a motor should be grounded, the shaft needn't be tested.

I'm slightly shocked that the depicted control panel box doesn't have any visible green/yellow wire,
or designated ground-connect post or busbar.

 

[mksj]

Evidently the NEC electrical code permits the grounding to the machine through metal rigid conduit as well as some forms flexible metal conduit but with limitations for the latter. I typically use a central/star grounding point at the power entrance to the machine. I grind off the paint on the control system back plate and then attach the nut with a star washer, add a washer stack the ring terminals from the machine/line grounds than another washer, star washer and nut. This includes the motor(s) ground(s). Alternative is a ground bus bar or plate. There also may be local electrical code that applies. Bottom line is you want a securely low impedance grounding to the machine. Since I have used some form of flexible wiring/conduit to my machines, I use a separate ground wire from my machines to the power source. I had an older house that used flexible metal armored cable as the ground, but the connections at the boxes became corroded and a bit sketchy over time.

NEC 2023 Basics: Equipment Grounding Conductors - Technical Articles

Learn about equipment grounding and types of equipment grounding conductors.

eepower.com

 

[machinistnoob]

Evidently the NEC electrical code permits the grounding to the machine through metal rigid conduit as well as some forms flexible metal conduit but with limitations for the latter. I typically use a central/star grounding point at the power entrance to the machine. I grind off the paint on the control system back plate and then attach the nut with a star washer, add a washer stack the ring terminals from the machine/line grounds than another washer, star washer and nut. This includes the motor(s) ground(s). Alternative is a ground bus bar or plate. There also may be local electrical code that applies. Bottom line is you want a securely low impedance grounding to the machine. Since I have used some form of flexible wiring/conduit to my machines, I use a separate ground wire from my machines to the power source. I had an older house that used flexible metal armored cable as the ground, but the connections at the boxes became corroded and a bit sketchy over time.

NEC 2023 Basics: Equipment Grounding Conductors - Technical Articles

Learn about equipment grounding and types of equipment grounding conductors.

eepower.com

View attachment 475804

So, that stud that you circled would be a good place to connect and verify a ground?

 

[mksj]

Yes, but be sure to remove the paint under the nut so there is a solid ground, there also should be a ground wire from that post to the motor ground lug. I use ring terminals so they cannot wiggle out when stacked and you tighten the nut. I ground off the paint on both sides of the back plate, threaded a bolt through, which is locked to the back plate with a star washer and a nut, so a secure post which the ground wires are connected two. Alternate for bare solid wires is a grounding bus bar seen in electrical panels that are screwed to the back plate. But that post should be OK, just remove the paint around the nut.

 

[machinistnoob]

Yes, but be sure to remove the paint under the nut so there is a solid ground, there also should be a ground wire from that post to the motor ground lug. I use ring terminals so they cannot wiggle out when stacked and you tighten the nut. I ground off the paint on both sides of the back plate, threaded a bolt through, which is locked to the back plate with a star washer and a nut, so a secure post which the ground wires are connected two. Alternate for bare solid wires is a grounding bus bar seen in electrical panels that are screwed to the back plate. But that post should be OK, just remove the paint around the nut.
View attachment 475847

Thank you very much!

 

[machinistnoob]

Thank you all, for your time, wisdom and insight!

 

[whitmore]

Yes, but be sure to remove the paint under the nut so there is a solid ground,...

I'm not sure the surface 'under the nut' there is metal; looks like a nonconducting base
for attachments. I'd expect a major casting in such a machine to have an easy-to-find
ground attachment feature. Star washer between two painted OR plated metal surfaces is good, it penetrates paint
reliably when tightened.

 

[machinistnoob]

I'm not sure the surface 'under the nut' there is metal; looks like a nonconducting base
for attachments. I'd expect a major casting in such a machine to have an easy-to-find
ground attachment feature. Star washer between two painted OR plated metal surfaces is good, it penetrates paint
reliably when tightened.

You are correct. It a composite board which is hung and mounted on those bolts. Those bolts fastened into the casting blocks behind it. I hooked up to and tested at the lower left one. With everyone's help, this elementary task was successful.