Grounding question

[btburn]

I searched around and couldn't find an answer.
I have a Dynatorch Super B 4x4 table, I live in Colorado.

I put in a 5/8"x 8' ground rod in and when I did the ground test from the manual I was at 6V. The Manual say's I need to be under .75V.

The test is hooking a 100W incandescent bulb to the 110V outlet hot side and the other bulb wire to the machine ground then testing voltage between the machine ground and the neutral wire.

I sank a 2nd rod and it brought it down to 3V
I sank a 3rd rod and it brought it down to 2V
The rods are 8' apart and wired using 4ga stranded sheathed copper wire.
The closest ground rod is about 4' from the machine then the other rods connect to that rod.

It's dry out here but I didn't think our soil was that dry.

The ground to neutral voltage on the household 110V outlet and breaker box ground rod is at around .3V

My question is: Should I continue sinking rods?
Or is it acceptable to ground to my copper plumbing to get where I need to be?
Am I missing something?

The bulb I have is a cheapo 100w bulb so it may not be a true 100w bulb and we don't have any other 100w bulbs to test that theory.

Dynatorch is closed right now but I will call them in the morning if no one here has suggestions that I can work on until then.

[Largemouthlou]

Try watering the ground rods and see if the readings change.

[btburn]

I am doing that right now letting it soak in while we eat dinner. I'm going to let it run for a while and check it before bed.

[acourtjester]

Two things come to mind grounding to copper plumbing will do nothing for you if the plumbing does not have metal going completely from your shop for a large distance away. Many water supply systems are not metal these days if you have copper in your shop there may be PVC supply plumbing coming in.
The ground in you breaker box is better then the ground rods you are sinking you need to find out why. Is the wiring from your breaker box and the machine correct? If you open your breaker box many hook the ground and neutral together in the box.

[btburn]

The grounding in the breaker box is good but they said to have a separate ground just for the table within 20'

[jimcolt]

The grounding in the electrical panel is there for completely different reasons than the suggested "Earth ground" for the cnc machine secondary wiring. The earth ground rod at you machine is there to attenuate stray voltages (that are produced in the drive electronics, the plasma power electronics as well as stray voltages from other shop equipment) and force them back to an earth ground. This will make for better operation of the machine electronics with less opportunity for machine interuptions or even damage to sensitive components.

Best bet of course....is to contact Dynatorch and ask them for advice as they designed the machine.

Jim Colt Hypertherm

[WyoGreen]

I was told by an electrical inspector in Colorado that a good ground source was the rebar in the buildings concrete footings. Probably a little late to add a connection to the rebar now though.

[btburn]

Ok, So now I have 5 ground rods spaced 10 feet apart, all joined together and I'm at 1.2V.

I tried watering them and it didn't make a noticeable difference.

The voltage when I do a test on the house socket using the garage and the same test reads at .3V.
I have no Idea why there is such a difference in grounding qualities of the soil 50" apart from each other.

I'm going to give a local electrician that is familiar with my area a call tomorrow and see if I can get some insight before I drive more ground rods to reach my goal of <.75V.

Does anyone else have a grounding problem?

[acourtjester]

As you see grounding is affected by many issues local conditions being one for you. Conductivity seems to your problem when the electrician show ask him how long the ground rod is for the service for your home 8? may not be long enough. This may be at your home or at the power pole that supplies your service. Adding more rods will not solve your problem if the soil will not conduct.

[jimcolt]

I strongly recommend against more than one ground rod. Again, I suggest you get advice on this from the manufacturer / designer of the machine.

I have been involved with installations of cnc plasma cutters for well over 30 years. There, even with a high frequency start system, is no need for multiple ground rods....in fact multiple rods can cause ground loop issues which can exacerbate noise issues (from my personal experiences).

I suspect your Dynatorch system using a non high frequency start plasma would operate just fine with the original single ground rod that you have installed.


Jim Colt Hypertherm

[CNCCAJUN]

A retired AT&T guy that works part time @ my local hardware store suggested the below.

He used to install cell towers all over the country so he is probably pretty familiar with grounding problems.

Below is a copy and paste from a manual outlining what he explained to me.

Soil Resistivity

Soil resistivity can be changed in two ways: by altering the mineral content, the moisture content, or both.
The ideal solution to poor soil resistivity is to excavate the immediate area and backfill with conditioned soil
additives. In extremely dry areas, the moisture content can be improved by installing a drip system which
continually moisturizes the soil surrounding the ground rod. A crude way of affecting soil moisture and content
is to use salt water, or rock salt to condition the surrounding soil.

[Shane Warnick]

I strongly recommend against more than one ground rod. Again, I suggest you get advice on this from the manufacturer / designer of the machine.

I have been involved with installations of cnc plasma cutters for well over 30 years. There, even with a high frequency start system, is no need for multiple ground rods....in fact multiple rods can cause ground loop issues which can exacerbate noise issues (from my personal experiences).

I suspect your Dynatorch system using a non high frequency start plasma would operate just fine with the original single ground rod that you have installed.


Jim Colt Hypertherm

I was going to post on this last night about the ground loop issue and got busy with the kids and forgot. I second the caution with more than one ground rod, especially no farther apart than they are. You can creat a ground loop and baiscally make it into a huge antenna that will cause EMI or stray voltage to chase itself around the loop. Especially if your soil is not real conductive. I would say spend money on a power supply / universal battery backup with a power conditioner built in, and use that to run the table and the computer, most people (myself included) have great results with this. You can search for my posts and find a rather lengthy thread about that on here that was in the last month or so.
Shane

[Stout]

In south Texas hill country I live on a rock. So grounding was certainly an issue. On my first CNC, an Esab system, they documented how to get the best ground by testing with a 100 watt light bulb. I'm sure you can look it up.

I wound up going with a Ufer ground where you tie into the rebar of the slab. The concrete is acidic and promotes contact between the rebar and soil. It worked OK with the Esab system, which used hi freq to start, and absolutely no problems with the new Hypertherm CNC system.

[btburn]

OK, I got it. Dynatorch had me connect my machine ground into the utility box existing ground.
I also picked up an UPS to plug everything into. I got my first cut and I just need to learn the ins and outs of the machine.
I appreciate all the advice here.