Electricity safety questions

Discussion in 'General Electronics Chat' started by UnnamedUser159, May 29, 2016.

  1. UnnamedUser159

    Thread Starter Member

    May 3, 2016
    130
    0
    Hi there.
    Before a long time i had some fears about safety and electronic devices - thoughts about someone will be hurt if i dont be carefull enough and so...
    I have some questions which answers gonna make me feel good and confident.
    Right now the questions are about lcd monitors...
    here`s example from today:
    https://flic.kr/s/aHskAFJ9pR
    i put the board in this black frame. is something missing like some plate?
    Part two :
    if we watch the boards:
    - the right board - there was three holes for screws. i think there was signs like sun(look uploaded picture in the end of post) on the front size.
    - on left board - there was 4 holes for inserting screws, but these "suns" are on the back side of the board
    Why there is a difference of the sides on the two boards ?
    i see one general screw which connects metal part with power bush(port).
    And the general question : what are really they for?
    About nulling the boards so the both boards and display can work normal and for safety ?
    What safety for example ?

    Here`s the picture of WWW(please zoom it) : https://flic.kr/p/HCDAB2

    Thanks in advance !
     
    Last edited: May 29, 2016
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,762
    924
    The "suns" are called star washers. They insure a good metal to copper contact and are to put the chassis ground and power ground together for safety of the user. They are located on top or bottom as required by the location of the copper on the board.
     
    UnnamedUser159 likes this.
  3. wayneh

    Expert

    Sep 9, 2010
    12,085
    3,024
    Your question is very hard to understand. Can you be more specific - one thing at a time - and show a picture of just what you are asking about?
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,085
    3,024
    Ah, Kermit beat me to it. I suspected the lock washers.
     
    UnnamedUser159 likes this.
  5. UnnamedUser159

    Thread Starter Member

    May 3, 2016
    130
    0
    Hm Hm :)

    Do i understand right ? The screws on boards 1 and 2(in monitor case) are for the they to be grounded and then the grounding cable which is connected to third wire is just connected to the chassis to put everything "out"(to the power network,"wall")?

    Is there some safety function in this case? The monitor housing(case) of course is plastic.

    Nice Day.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,494
    2,364
    The method of fixing component frames etc to a metallic enclosure with star washers is to achieve something known as equi-potential bonding (to earth), this is more to reduce the chance of ground loops etc, as well as the grounding safety aspect.
    With a plastic enclosure this is not easily possible, but the frame should normally be earth grounded.
    http://electrical-engineering-portal.com/purpose-of-equipotential-bonding
    Max.
     
    Last edited: May 30, 2016
  7. ian field

    Distinguished Member

    Oct 27, 2012
    4,412
    782
    Primarily star washers are "shakeproof" - but they're *MUCH* better for making a good earth connection than shakeproof spring washers.
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,085
    3,024
    We're talking about the ones in the middle, right?

    lockwashers.jpg
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
    4,412
    782
    The middle one is best for making an earth connection by a bolt through painted or plated chassis.

    The internal star on the left is not as good for earthing and is more popular where you don't want to spoil the finish around a fastener.

    AFAICR: the earth bolt cannot be in *ANY* way structural - that even goes as far as you can't just bolt the earth tag to the chassis. The bolt goes through the chassis with a fixing nut that serves only that purpose, the external star goes under that nut. Once the earth bolt is so secured; the earth tag is fixed with a nut all of its own - that nut has the split washer and at least one plain washer.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,494
    2,364
    This is another very good source by Siemens.
    Max.
     
Loading...