[Simonh1959]

We have a Techserv Blue Marlin plasma table and I am getting a Hypertherm Powermax 105 to use with it. I have read numerous posts about fitting an earthing rod which seems a good idea to me.
I know that it is better to have the rod as close to the machine as possible but that would mean drilling through the factory floor which in itself is not a problem but as the place was built in the 1940's I would have thought that the ground under the floor is going to be very dry. I would like to put it just outside the building but that would be about 10/12 metres from the machine and I was wondering if this would have any detrimental effect. I have some 16mm diameter solid copper bar that I intend to use but what size/type of cable would be best to connect up with? Also, where is the best place on the table to connect this earthing wire to, my return cable from the Powermax is bolted directly onto the support bars at the end of the bed, should I connect the earth to the same place?

[Al_The_Man]

Normally any suitable place on the table is used, and you can usually get multi-stranded welding cable for a suitable conductor, make sure the incoming service ground is also connected to this point.
Al.

[jimcolt]

The whole ida of an earth ground is to route any stray voltages on as direct and easy of a path to ground. Electricity will always follow the path of least resistance....so for an earth ground to be as effective as possible....it must be close to the source of these voltages, the cables running to it should be as large as practical and as short as possible.

Ideally....a ground/earth rod should be as close to the cnc cutting bed as possible. All connections from electronics chassis, plasma power supply chassis, as well as machine gantry and torch carriage should be made with stranded wires (the type of electrical noise that often causes issues with sensitive electronics and computers is Radio Frequency, or RF. RF travels on the outside of conductors.....stranded cables have multiple conductors...so have vastly more surface area to conduct...making them a better carrier than a single strand cable). All cables should connect to a buss bar on the ground rod.....this includes the Plasma work cable. Another cable of the same type and size as the plasma work cable then should go directly to the slat bed on the cutting machine.

So, as close as possible, as short as possible, stranded heavy gauge wires....and you will have the best solution to reduce the possibility of electrical noise interference. Often....cnc machine manufacturers will be able to provid a document that describes best practices for eart grounding a machine.


Jim Colt Hypertherm

We have a Techserv Blue Marlin plasma table and I am getting a Hypertherm Powermax 105 to use with it. I have read numerous posts about fitting an earthing rod which seems a good idea to me.
I know that it is better to have the rod as close to the machine as possible but that would mean drilling through the factory floor which in itself is not a problem but as the place was built in the 1940's I would have thought that the ground under the floor is going to be very dry. I would like to put it just outside the building but that would be about 10/12 metres from the machine and I was wondering if this would have any detrimental effect. I have some 16mm diameter solid copper bar that I intend to use but what size/type of cable would be best to connect up with? Also, where is the best place on the table to connect this earthing wire to, my return cable from the Powermax is bolted directly onto the support bars at the end of the bed, should I connect the earth to the same place?

[Simonh1959]

Thanks to both of you for your sugestions. Jim, you say that stranded heavy gauge wire is best, would you recomend simply using a large diameter welding type cable which has many strands but are of relativly small diameter or do you think that a large multistranded earth cable such as the ones used by electricians for wiring buildings would be better. The latter type would have less strands but heavier gauge wires.

[jimcolt]

More strands are better for routing RF noise back to an earth ground....so the multiconductor welding cables are definitely better, however are also more expensive.

You are specifying the use of a Powermax105 plasma....which is a blowback start plasma with no high frequency starting. While it is my opinion and experience that all cnc plasma cutting machines should have a good eathgrounding system....you do not generally have to ground things as thoroughly with this type of plasma asyou would with a high frequency start, high voltage start or a capacitive start plasma. Best bet is to speak with the techs from the builder of your machine to get their advice / experience....as all machines have varying levels of sensitivity to electrical noise.

Jim Colt Hypertherm

Thanks to both of you for your sugestions. Jim, you say that stranded heavy gauge wire is best, would you recomend simply using a large diameter welding type cable which has many strands but are of relativly small ameter or do you think that a large multistranded earth cable such as the ones used by electricians for wiring buildings would be better. The latter type would have less strands but heavier gauge wires.

[Stout]

I had serious issues with grounding using my old Esab PCM1000 power supply with hi freq start. It's all limestone where I live and not a good conductor. Eventually went to a Ufer ground which utilizes the rebar in the slab. It worked well. I just chipped away at the base of the slab until I got to the rebar, then welded a tab onto it.

My electrician had issues with me putting a separate machine ground near the plasma table. According to him, there can be only one ground in an electrical circuit. Don't know the reasoning..

Ufer ground - Wikipedia, the free encyclopedia

[jimcolt]

The Earth ground required on cnc machines has nothing to do with the safety ground that is required for the input electrical system. Rather...it is designed to provide the easiest path back to earth for stray electrical noise (RF, or radio frequency) that can affect sensitive electronics and computers.

Jim Colt Hypertherm

I had serious issues with grounding using my old Esab PCM1000 power supply with hi freq start. It's all limestone where I live and not a good conductor. Eventually went to a Ufer ground which utilizes the rebar in the slab. It worked well. I just chipped away at the base of the slab until I got to the rebar, then welded a tab onto it.

My electrician had issues with me putting a separate machine ground near the plasma table. According to him, there can be only one ground in an electrical circuit. Don't know the reasoning..

Ufer ground - Wikipedia, the free encyclopedia