Proper Grounding

I'm wanting to put an earth ground in for my machine. I currently don't have one, and have the machine grounded to the metal inside of my electronics enclosure and then from there to the electrical ground. I was wondering when I put in a grounding rod, if I should then take the grounding wire out that runs between my box and the table itself. My electronics enclosure is plastic so it is isolated from the table other than the ohmic wires. I'm in a rented building and my landlord will not allow me to drill any holes in the floor or the wall of the building for a ground rod. My table is right next to an overhead door, and I was thinking that I could run a grounding rod outside and run an insulated wire between the table and the grounding rod itself and just run the wire underneath the edge of the door where it would just sit between the weather strip and the floor. I never open this door, so it's not a high traffic area by anymeans. The total distance would be 10-15 feet (3-4 meters) form the table to the grounding rod. Is there any specific type of grounding rod that I should try to use (copper?) and should I use copper wire or will aluminum wire work? Also, is there a certain diameter grounding rod that you would suggest? I ran my entire business for three years on my last machine without a grounding rod, and never had an issue, but I thought that it may be a good idea as a safety measure for my new machine. I just want to be as cautious as possible. Thanks in advance, and thank you for making this forum as helpful as it is.

Hi
If i understand you correct you have a protective "earth" wire, coming from your supply?
And you wonder if you should additionally try to find a better "earth"?

Why? What is your problem? EMV?

Making a real good ground is not so easy. Just some mm2 of copper to a metal that is guessed to be solid eath is not a solution. You need massive copper with fx. Low inductance..
Mike

This would be a question better asked of an electrician in your area. It may cost you a few $$$$.

As this is a multi national forum and electrical rules vary from country to country, getting proper advice from a professional in your area would keep you in line with code and keep you safe.

Probably not the advice you want, but we all want to keep safe.

If you live some where with proper electrical codes and mandated installation inspections, your main panel should already be properly grounded, connect to that.

No, I definitely appreciate it. I wasn't even thinking of that, but that's a good point.

First off, this only applies to the USA.

"Supplementary grounding electrode
Section 250.54 of the NEC permits a grounding electrode to be connected to an equipment grounding conductor, as described in 250.118. Essentially, this allows for localized earthing to hold the electronic equipment ground to the same value as the local ground nearby that equipment. You can consider this application as an added value for safety grounding (voltage equalization) at or nearby the equipment. However, the NEC doesn't mention EMI considerations for this application. As the terminology implies, the NEC considers this application only as a supplement to all other grounding and bonding requirements that apply. The supplementary grounding electrode should never be used as the sole grounding means for the equipment."


Now you need to ask yourself some questions:

1) Do you actually need it? A quick way to check is to measure the voltage between the ground of an outlet and the metal case of your machine. Anything above a small handful of volts should be looked in to.

Be forewarned that the ground on the power side of things might be the culprit. In my buddy's shop it's about 60 volts from the wiry type of ground to the earthy type of ground.

Yeah, I've mentioned that there is a problem (pretty much right after I got popped while doing some soldering - which was a first for me). I even offered to fix it for him since I have a few papers here at the house that allows me to claim that I'm qualified. Maybe one day...


2) Are you ready to accept liability for anything that happens from this point on? The owner of the building will have a leg to stand on if something - even clearly unrelated - happens. Anywhere.


With that out of the way, a "proper" grounding rod for this application is a 5/8" x 8' copper clad rod. It needs to be driven flush with the ground a few feet away from the building. And these days you are required to either verify that the resistance to earth is 25 ohms or less (the test gear for this looks like something out of a science project), or you have to drive a second ground rod at a minimum of 10 feet away (IIRC, it's ten feet). You have to run the ground wire from one ground rod to the second one without cutting the wire.

The only acceptable connection methods that I am aware of is either a "ground rod clamp" (not be confused with a water pipe clamp), or by exothermically welding your cable to the rod (aka "Cad Weld"). Something that I wasn't aware of is that CadWeld apparently has a system for welding aluminum to copper. Huh, learn something new every decade...

If you use a ground rod clamp (the sane approach), then you need to use #6 bare solid copper (it has to be copper) to the ground rod.

We won't discuss the less than sane approach since the cost of renting or buying the CadWeld gear, and the chance of setting the building on fire isn't worth it. I've done CadWeld connections before and expect to waste a few shots before you get the hang of it. It is cool though.

Does it need to be inspected? Meh. If it was my building, hell no.

Don't think for a minute that your local "AHJ" (your inspector) is any expert on grounding. He or she is just someone who got themselves a cushy job with the city. However, since it isn't your building, I wouldn't even dream of doing it without an inspection.

A note on your inspector (also known as the "Authority Having Jurisdiction"), their word is law. It's as simple as that. Period.

And if it happens to be the correct call on their part, so much the better.

I do not think there is any benefit to be gained by adding a ground rod to a modern blowback style torch like the Hypertherms (which I think you have) and Thermal Dynamics. I would not waste time on it.

Thanks Rod! I know that I've read about the importance of them with high freq machines, but I wasn't sure if there would be any benefit of doing it with a blow back style torch. Thanks again