This is a short warning with information how to solve the issue.
More and more machines are delivered with deadly configuration on the grounding of the electronics.

In China, the electric standard is not well built and many houses still do not have ground solutions in their house. So the machines are built by their standard, when we in EU or US or other parts of the world often have a good ground setup already in our homes since many years.
If you have a 3-prong outlet from your wall, you do not need (and should not) ground it from the ground bolt.

Important information

This guide expect that your ground wiring where you have the laser is up to code.
If you are uncertain your ground are safe in your house – consult a electrician.

The problem

The internal electronic parts are grounded to the ground bolt in the rear of the machine, so is the ground line in the cable you plug to your wall outlet.
But, the bolt itself are often isolated from the machine case which is a big problem, first off for your safety, second for the current regulations and laws about machines with high voltage.
In China they do this because the grounding is external and not inside the cable from their wall outlets. But for us who think the case ground is properly done – it can and will kill you!

k40 ground bolt martin samuels
Ground bolt on the K40 laser machine with external ground. Not needed if you have proper ground in your wall outlet!

How to identify and fix this problem

Start with removing the ground bolt from your machine.

Use abrasive paper or a knife to scrape away some paint around the hole for the ground bolt. Both inside and outside.

Remove ALL plastic/nylon washers from the ground bolt, only use metal washers.
Some bolts has a plastic spacer, you might need this.
Here is a layout that will give you a good ground connection.

Now mount the bolt in your machine again.
The lock nut will ensure your bolt never comes off again. You can also use loctite or two nuts.

Here is a picture how a good ground bolt is fastened to your machine.
I use two toothed/serrated washers closest to the metal.
k40 ground bolt fix

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20 thoughts on “Warning for new machine owners – grounding issues”

  1. Is this meant for US owners also? House is grounded. Do I need to perform these steps but not use the ground from the post on the machine? I see a loop back to the grounding.

    1. For everyone. You do not need a cable on the outside of the machine if you have 3 prongs from your wall outlet. Just make sure the metal is clean so the ground bolt has proper connection. This is where the ground from the wall is bolted down, it has to be 100% good contact.

  2. I have just installed a new K40 laser in my shed. I intend to do the upgrade once i am confident with using the laser but for now i’ll use it as it is. I have everything connected but noticed (by accident) that there is a slight electric shock coming from the casing. I live in the UK and have a 3 prong plug for the power supply… Can you advise what I need to do? I am not knowledgeable what-so-ever with electric so please use easy terminology. Thanks

    1. Read the electric warning article i wrote a while back, in the FAQ menu. The problem is often the ground bolt in the back beeing isolated from the casing, this is where the ground from the wall outlet should have 100% contact with the metal. Take a look in the article and follow the steps and it will probaly solve your issue. If not, you have bad grounding to your shed.

  3. À lot of the K40 machines i’ve seen have the CE mark on it meaning that it
    Should have been tested accordingly to the CE safety standard.
    The chinese give à damn About these safety standards, just look at the cheap
    LEDs for 220volts, a lot of them can be simply touched on the 220v parts.

    À big compliment About Your website, very helpfull, thanks.

    1. Fake CE markings, some call it “chinese export” and not the real Conformité Européenne

  4. Didn’t quite understand where the grounding cable must go when inside the machine!
    Can you please explain where it will go?

      1. But if I read this right, you do NOT need to run a wire to an external earth ground if you have a three-prong outlet, like we have here in the US, correct? I have one of the larger Redsail x700 clones and my electrician installed an exterior earth ground when I had him wire a dedicated 20a circuit for the unit. There is a stiff copper wire that enters the basement through the exterior wall and I run a wire from the ground terminal on the back of the machine to the connector on the external earth ground. Is this overkill???

        Also, I’m guessing my case ground post is not making good contact. There was paint on both sides and the bolt had plastic insulators on both sides of the case. That tells me the only contact between the case and ground bolt was the edge of the hole drilled into the case.

        Would appreciate your feedback!

        1. If you have a ground rod, use it. If it´s overkill or not depends on your buildings ground status.
          Remove all plastic shit and remove paint and ground the machine case properly and it works great, no matter if you use the ground rod or a good wall outlet ground.

  5. Hi

    I have had a k40 for a few months but only just set it up. It does not work. I followed your grounding instructions with the nasty blue wire supplied but still no luck. The gantry works well and there is power to the sight dot which is not good. When I test fire there is a clicking sound and I think there is some blackening at the business end but no laser. Frustrating. I have a feeling there might be water in the wrong places too but not crack and no water leak. Where should I not see water? Thanks in advance.

    1. Try put a jumper between P and GND, or P+ and P- depending on PSU. This will disable the safety feature, some machines has a flow sensor on this, some is just bridged.

  6. I can give the electrical safety theory behind this. Here’s the danger scenario that is prevented by this upgrade:

    1) The machine gets some internal damage, such that a high-voltage wire starts touching its metal case (for example, the laser tube breaks and the high-voltage line of the laser supply touches the case). The case is now just sitting there with a high voltage relative to the earth, waiting for you to touch it.
    2) You’re standing on the earth, so your feet are somewhat connected to the earth.
    3) You touch the case. Now there’s high voltage between your hand and your feet, causing a current to flow through your heart. The amount of current flowing from the machine case to the earth through your heart depends on how well your feet are connected to the earth, but it might be enough to kill you.

    The standard solution (in well-made equipment) is to prevent part 1 of the scenario. The manufacturer connects the machine’s metal case to the earth via your house’s ground wire (the center prong on the three-prong plug). Now, if the damage in part 1) happens, current will immediately flow to earth through the ground wire. Thus, an electrical fault CAN’T charge the case to a high voltage relative to ground, because the case is connected directly to ground.

    In other words, the ground wire forces the case to the same electrical potential as the earth (and you) so that touching the case won’t shock you. (Another way to look at it: the grounding wire provides a much lower-resistance path to the earth than your body does, so 99.999% of the current flows through the grounding wire and not through you.) Your clothes dryer, power tools, etc all have grounded cases for this reason.

    On my K40 I confirmed that the red external ground plug is connected to the house wiring’s ground, but the metal case is NOT. So, the point of this upgrade is to properly connect the metal case to earth ground.

  7. This is so helpful. Just got one of these and was worried about the earth ground in manual. This is much better solution. Definitely want to be safe using this thing. My house was built in 2003 in USA so it has all grounded outlets. I was wondering why it would need additionally grounding. Now I have to find a way to tell my husband thAt I bought this machine…

    1. Show him this website and he´ll probably be okay with it as a safe machine to use, and probably join you with the adventures making stuff with it 😉

  8. People are getting confused because it reads like if you live in the US or UK you don’t need to use the rear ground bolt. While this is true, the bolt still MUST be in good contact with metal case. Look at the inside near the plug input. The ground from the 3 prong connection swings over to the bolt. So Even if you live in the US and do not plan on running a wire from the rear of machine to a ground, it is still being used, the 3rd prong connects to it.

  9. This s quite a nice forum.

    my laser engraver JK-1390, stopped burning while running
    the gantry is okey. But the laser power is off or simply a little pulse at the corner. BUR have realised its not earthed.
    how can I solve this problem?

    1. Start with following the guide above, you need to make sure you have it grounded.
      After that you can start by checking out the “no fire troubleshooting” guide to find out more what your machine can have trouble with.
      If the beam is weak or just pulses for a half second, your tube or PSU might be out. But focus on the grounding first, then look in to the problems. It might be the cause of killing the tube for you.

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