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Discuss Ground rod and EMI issue in the Electrical Forum area at ElectriciansForums.net

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Hi guys.

Im from Denmark. I just signed up in here, and I have a question about how to test my ground rod.

I dont have any electrical experience, but im really trying to learn. so please bare over with me..

Well I have a cnc plasma projekt that I have problems with.

The problem Is when i turn my plasma on, It causes my cnc program to frees and error pops up. I have to restart everything, try again and same problem over and over again.
I look In some forums, and it seems like something called EMI is a huge issue on HF Plasmas (Never heard off EMI before)
It seems like other people change there wires to shielded wire, and improved there ground.

So I tough If I change my wire and make a brand new ground stick I would be over that problem. BUT NO NO!! Stil the same issue.

So now I think i maybe should test my new ground for the plasmatable. I only got a cheap multimeter, so I read how to do it easy with that.

But why do I get 0.258 Vdc when i stick new ground rod and neutral together? and -0.04 Vdc when old groundrod (2 years ond) and neutral together?

Hope you can help here.? :)
 
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James

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Is this a home built project or a purchased machine?
If you have purchased it, the instructions are a great place to start.
If you have built it then can you post some pictures of the electrical control panel?
 
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Is this a home built project or a purchased machine?
If you have purchased it, the instructions are a great place to start.
If you have built it then can you post some pictures of the electrical control panel?
It is a purchased CNC laser, that i have build a plasma on.
 

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James

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make sure that the ground connection for the plasma torch is kept separate from the other ground connections.


there are so many ways that the high frequency could be getting to the pc systems

you might find that physically moving the cnc control box well away from the plasma generator will help.

where you have cables feeding the plasma head, do not run them together with any servomotor cables or feedback cables.

probably better to put the cnc on one side of the base and the plasma generator on the other side, that way you separate the cables as best you can.

shielding on the cables will help but ensure that the shields are not connected to each other apart from at the relevant control panel.
all shields should be attached to ground at the control panel end of the cable.

where you have to have plasma head power running close to other cables, make the run as short as possible, try not to run them parallel to each other and if you can have a grounded metal plate separating them, even better.
 

Megawatt

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Hi guys.

Im from Denmark. I just signed up in here, and I have a question about how to test my ground rod.

I dont have any electrical experience, but im really trying to learn. so please bare over with me..

Well I have a cnc plasma projekt that I have problems with.

The problem Is when i turn my plasma on, It causes my cnc program to frees and error pops up. I have to restart everything, try again and same problem over and over again.
I look In some forums, and it seems like something called EMI is a huge issue on HF Plasmas (Never heard off EMI before)
It seems like other people change there wires to shielded wire, and improved there ground.

So I tough If I change my wire and make a brand new ground stick I would be over that problem. BUT NO NO!! Stil the same issue.

So now I think i maybe should test my new ground for the plasmatable. I only got a cheap multimeter, so I read how to do it easy with that.

But why do I get 0.258 Vdc when i stick new ground rod and neutral together? and -0.04 Vdc when old groundrod (2 years ond) and neutral together?

Hope you can help here.? :)
Hyper that plasma machine needs to have its on dedicated circuit with nothing wired to it
 

Wilko

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So now I think i maybe should test my new ground for the plasmatable. I only got a cheap multimeter, so I read how to do it easy with that.
Hi - unfortunately you can’t test the impedance of your earth rod with a multimeter. Electricians usually have the right equipment to perform the test.
 
have you got access to a UPS; if you have you can use it to filter the power to the device running the program.
 
It is a purchased CNC laser, that i have build a plasma on.
Looking at the photos I am not surprised you have problems. The control electronics should be in their own solid metal screened enclosures and well away from the power leads. Earthing should be back to a single star ground point. Signal and control commons (0 volts) should be separate wires inside screened cables and the screens only connected at one end of cables to the star point.

EMC/EMI issues are very complex and a mixture of deep EMC knowledge and plenty of practical EMC experience. You can't just lash things up like that in a plastic box and expect it to work just fine. It generally will not do so. It will have little (if anything) to do with your Ground Rod. You will also need FAR more than just a multimeter and also the experience and knowledge how to use EMC diagnostic equipment including RF sniffers and spectrum analysers if you still had problems after building it in a proper manner in metal screened boxes and suitable well routed cabling, which may be all you need to do to get it to behave.

In my opinion the best book by far is 'EMC for Product Designers' by Tim Williams. EMC for Product Designers: Amazon.co.uk: Tim Williams: 9780081010167: Books - https://www.amazon.co.uk/EMC-Product-Designers-Tim-Williams/dp/0081010168/ref=sr_1_1?keywords=EMC+for+product+designers&qid=1568580182&s=books&sr=1-1 The first Ediion was written in 1976 and the latest 5th Edition in 2016. It is 550 pages and quite expensive but is an excellent guide.
 
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