Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 27

Thread: Earthing equipment questions

  1. #11
    Diamond Member
    Join Date
    Mar 2010
    Location
    Cape Town
    Posts
    6,329
    Thanks
    426
    Thanked 978 Times in 795 Posts
    @bones - Thank you for your truly interesting take on the workings of a modern laser cutter. May I be so bold as to ask you where you obtained your information? I really need to brush up on my poor understanding of such matters.

  2. #12
    Diamond Member
    Join Date
    Mar 2010
    Location
    Cape Town
    Posts
    6,329
    Thanks
    426
    Thanked 978 Times in 795 Posts
    Andy, we are talking about two different machines. The static electricity issue is not on the laser, it is on a totally different machine.

    What I don't get is howcome I feel the tingling sensation when I am not grounded and only running a finger over the machine. The sensation isn't present when I touch the machine and hold my finger still.

  3. #13
    Diamond Member AndyD's Avatar
    Join Date
    Jan 2010
    Location
    Cape Town
    Posts
    4,923
    Thanks
    576
    Thanked 934 Times in 755 Posts
    Ahh, I thought it was the laser cutter. Makes no difference though, I'd still suspect poor/no earth and either an insulation fault that may or may not need fixing or functional leakage that should be measured but probably would be acceptable.
    _______________________________________________

    _______________________________________________

  4. #14
    Silver Member bones's Avatar
    Join Date
    Aug 2014
    Location
    Pretoria
    Posts
    223
    Thanks
    73
    Thanked 6 Times in 6 Posts
    Quote Originally Posted by AndyD View Post
    I'm suspecting that the earth terminal on the chassis that you thought was there as an optional extra in fact must to be connected to the supply earth (CPC). Obviously without any first hand knowledge of the machines or your electrical installation I may be incorrect but if you're feeling a static type shock I can guarantee you something is amiss and there's a potential hazard that should be addressed.
    my laser as i said has two plugs one for power
    with earth wire the other just an earth and i
    dont experience any type of static or power
    trips

  5. #15
    Diamond Member
    Join Date
    Mar 2010
    Location
    Cape Town
    Posts
    6,329
    Thanks
    426
    Thanked 978 Times in 795 Posts
    Quote Originally Posted by AndyD View Post
    Ahh, I thought it was the laser cutter. Makes no difference though, I'd still suspect poor/no earth and either an insulation fault that may or may not need fixing or functional leakage that should be measured but probably would be acceptable.
    I'll give the machine a twice over today.

  6. #16
    Diamond Member
    Join Date
    Mar 2010
    Location
    Cape Town
    Posts
    6,329
    Thanks
    426
    Thanked 978 Times in 795 Posts
    @Andy

    I had a look at the machine just now. The machine does not have any earth whatsoever. When I turn the machine on an measure the voltage between the chassis and te installation earth it sits at 110VAC. I see that even on the motion controller housing.

    It seems that the whole lot has been left to float for some reason.

    Could it be a function of the massive transformer?
    There is a green lead that comes from within the transformer core and is wired onto the body of the transformer - what is that all about?

    Click image for larger version. 

Name:	20151121_173054.jpg 
Views:	139 
Size:	62.3 KB 
ID:	6054

    Click image for larger version. 

Name:	20151121_173019.jpg 
Views:	149 
Size:	57.9 KB 
ID:	6055

    Click image for larger version. 

Name:	20151121_173027.jpg 
Views:	167 
Size:	37.0 KB 
ID:	6056

    Click image for larger version. 

Name:	20151121_173039.jpg 
Views:	139 
Size:	58.5 KB 
ID:	6057

    Click image for larger version. 

Name:	20151121_173044.jpg 
Views:	145 
Size:	30.7 KB 
ID:	6058

  7. #17
    Diamond Member
    Join Date
    Mar 2010
    Location
    Cape Town
    Posts
    6,329
    Thanks
    426
    Thanked 978 Times in 795 Posts
    I just had a thought, maybe one of the output phases of the VFD is shorting to the chassis somewhere along its cable run.

    Click image for larger version. 

Name:	20151121_174921.jpg 
Views:	141 
Size:	33.3 KB 
ID:	6059

  8. #18
    Diamond Member
    Join Date
    Mar 2010
    Location
    Cape Town
    Posts
    6,329
    Thanks
    426
    Thanked 978 Times in 795 Posts
    I checked the VFD and all its connections are OK.

    I got it sorted.

    I disconnected the VFD, transformer, coolant pump but the problem remained the same. Then I had a thought and it was to isolate the metal body of the motion controller from the rest of the machine....and suddenly everything seemed ok.

    So, I put a proper earth in to the machine chassis. I then reconnected each component in turn. That all worked fine. I then installed padding between the motioon controller and the machine chassis and bolted it down with plastic bolts.

    The machine is working happily and I no longer fear for my life.

    I can't say that I understand what is going on with the motion controller but it may be a function of the USB cable connecting to the PC. I should have checked to see what it would do if I just disconnected the USB cable but I didn't think of it at the time.

    I connected my TOPTRONIC ELCB / Polarity testers and everything seems good.

  9. #19
    Diamond Member AndyD's Avatar
    Join Date
    Jan 2010
    Location
    Cape Town
    Posts
    4,923
    Thanks
    576
    Thanked 934 Times in 755 Posts
    First the earthing. The transformer looks like it's a standard step down, it doesn't appear to be an isolating transformer with a screen so the earth wire connecting to the laminations should go to the supply earth (CPC), it's just for safety if the transformer ever goes faulty.

    From what I can see I'd say the chassis of the machine should definitely be connected to the CPC (the supply earth).

    Secondly the elevated voltage that was giving the static/tingling sensation. The 110v you saw on your tester is possibly misleading, probably what I'd call a ghost voltage if you were using a digital tester. You can take it as an indication of earth leakage but nowhere near as bad as the voltage may suggest. If you did the same voltage test with an analogue tester or a digital tester with a LoZ range you'd see a much smaller voltage being indicated. The voltage you saw could be caused by functional leakage, especially so looking at the internal components. The VFD, the constant current driver/PSU and the 4-axis USB motion controller are all candidates for having standing functional leakage. As I've explained elsewhere, functional earth leakage currents are not considered fault currents as long as they meet certain criteria. If the machine is now supplied via an RCD and the chassis is bonded to the supply earth then there's no reason it shouldn't be safe.
    _______________________________________________

    _______________________________________________

  10. #20
    Diamond Member
    Join Date
    Mar 2010
    Location
    Cape Town
    Posts
    6,329
    Thanks
    426
    Thanked 978 Times in 795 Posts
    I agree with you about the ghost voltage. I find it interesting that the machine was never earthed at all, seems that the person who said that one should be careful of Chinese machine earthing was right.

Page 2 of 3 FirstFirst 123 LastLast

Similar Threads

  1. Earthing
    By TECHNICIAN 810 in forum Electrical Contracting Industry Forum
    Replies: 16
    Last Post: 04-Apr-23, 04:53 AM
  2. The Earthing Terminal for Other Services.
    By Leecatt in forum Electrical Contracting Industry Forum
    Replies: 1
    Last Post: 20-Apr-15, 02:34 PM
  3. Earthing advice needed
    By IMHO in forum Electrical Contracting Industry Forum
    Replies: 7
    Last Post: 28-Mar-14, 12:44 AM
  4. Another earthing question
    By adrianh in forum Technology Forum
    Replies: 6
    Last Post: 16-Feb-14, 05:03 PM
  5. Earthing and the CoC
    By WallyL in forum General Regulatory Compliance Forum
    Replies: 11
    Last Post: 20-Jan-11, 12:06 AM

Did you like this article? Share it with your favourite social network.

Did you like this article? Share it with your favourite social network.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •