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  1. #21

    "Combining both of them wouldnt be a good idea."

    That's why I started this thread ! .. I didn't think it would be a good idea !

    I think Robin may have suggested to 'un'earth your cooker to make it safer ! lol :P

  2. #22
    Quote Originally Posted by Web Goblin View Post
    Robin, what part of this "rant" would cause someone to be killed due to electrocution?
    I like to add a disclaimer before I start to rant. If I guarantee death will follow my opinion I can hardly be blamed if proven correct.

  3. #23
    Quote Originally Posted by Want2build1 View Post
    "Combining both of them wouldnt be a good idea."
    Interesting question. Theoretically your generator has 3 phases all off earth. The three phases are divided up between the houses at your substation to try and equalise the load. Your single phase earth connection comes with your mains supply and you back it up by connecting it to a water pipe. The local ground is probably thus already in place, no spike required.
    The earth resistance is noted on the house certificate, usually calculated by distance and square mm rather than by measurement. The distance is measured back to the 25mA breaker which is why you see a lot of fat naked copper heading for the fuse box. Overkill makes the sums easy.

  4. #24
    unless you have a plastic water supply pipe :)
    We don't... old house.. but I still have 50m of reltively small cross section cable from the house to the shop.
    There will be, I would think, significant resistance in the earth wire.
    The cable armour is not connected to earth AFAIK (was installed before I moved here) It's 3 core, and the earth wire is my shop earth

  5. #25
    Robin, Ok I see what you mean now. RCDs are normally 30mA.
    Want2build1, the steel wire of the armour should have been connected at the supply end of the cable. This way the circuit protection would operate if someone drives say a pick or something through the cable and protect said person.
    If you are going to change the earth then you would need to connect the armour at the supply end only.

  6. #26
    I shall check the cable armour at the house box, when I get a chance :) Thinking about it, it should be earthed !

  7. #27
    typed at the same time !

  8. #28
    To add to this ...

    Recently my Laser PSU died.
    So, I've had to read up on PSU wiring, inputs and outputs ...

    The return wire from the tube is connected to the case/chassis !

    so, if you get a bad earth connection in the mains supply or plug - either end- then the chassis is potentially at 25Kv .

    Unlikely , you might think but ! ...

    I just bought a K40 laser machine as a backup. This arrived with a dud tube. The fault was a cooling water leak INSIDE the tube ! which effectively shorted the 25Kv HT to the chassis !

    Sooo .. I think the warning for the extra earth connection direct from machine to ground, is sort of a make do safety precaution, to cover this bad design 'feature' .

    When I realised this, I had to wonder how the RCD didn't trip, with a constant 20mA or so leaking to earth. I came to the conclution that the flyback transformer produces an isolated current, so the RCD wont protect you.

    It's kind of unbelievable that this is a designed situation, not a fault situation.

    So .. check your earth connections everyone !


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  10. #29
    and more to add ..

    Watching a blog vid of someone reviewing a laser in the USA, He stated he had to install the ground wire, as his house didn't have ground wiring !

    That was one of my 1st thoughts.. although I assumed the contries like the US would have ground wiring in their houses by now ?

  11. #30
    SWMS's Avatar
    Lives in Cardiff, United Kingdom. Last Activity: 04-02-2015 Has been a member for 1-2 years. Has a total post count of 3.
    If you bought the machine from China I would earth it using the spike. It could be that parts of the machine are electrically isolated from each other. In which case, knowing how they connect the laser tubes, I wouldn't fancy 25 volts bouncing around the frame. :) Basically as he above said. :)

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