Thread: Earthing?

Page 1 of 7 123 ... LastLast
  1. #1
    Hi again.

    I need advice on earthing, generally I am ok, but being new to electronics I thought I would get a second opinion.
    My question is this,my PSU, Drivers etc; are enclosed in a metal cabinet. I ordered an On/Off switch for the cabinet, it arrived with 2 poles only. The cabinet is powered from a 3 pin mains socket, can I use the earth cable of a 3 wire circuit, to earth the metal cabinet, by attaching the cable through a hole in the cabinet wall, and attaching with a bolt/screw?

    Click image for larger version. 

Name:	Slide1.JPG 
Views:	395 
Size:	25.3 KB 
ID:	6721 This is what I have now.
    Regards

    Ray

  2. #2
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 2 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,838. Received thanks 192 times, giving thanks to others 5 times.
    Your main earth wire should go to a central (star) ground point within the box, and should be permanently connected.

  3. The Following User Says Thank You to m_c For This Useful Post:


  4. #3
    A bit more information required. Are you directly connecting your power supply for the machine to the socket circuit or are you connecting it via a 13amp plug?

  5. #4
    Hi

    Thanks for reply, excuse my ignorance what is a STAR?

    Regards

    Ray

  6. #5
    Hi
    Thanks for reply, i am connecting via 13 amp plug.

    Regards

    Ray

  7. #6
    Quote Originally Posted by manofgresley View Post
    Hi

    Thanks for reply, excuse my ignorance what is a STAR?

    Regards

    Ray
    Hi Ray,

    Star means all AC Earths come from one point "Star point". This is very important so you don't introduce electrical noise into the system thru creating ground loops.
    The signals coming and going from control software thru the parallel port to drives or sensing switchs like home switchs etc are very sensitive to electrical noise. This has the affect of tricking the motors, sensors etc into false moves or switching when shouldn't and cause real head scratching problems.

    Mostly when people have missed steps or false e-stops etc it often turns out to be bad earthing practices. This is also why it's important to use sheilded cables for stepper motors and spindles ETC and correctly route back to the star earth point. (See quick pic showing)

    NOW don't confuse AC Earth with the " - " or negative of the DC side of the system. While they ultimately all go back to the same Earth point they should be treat has separate and any DC negatives are best taken from a DC negative point. IE from the BOB Com or " - " pin or the " - " negative of the DC side of a PSU.
    Often I'll run a single wire from the Main PSU DC negative to a distribution rail where I then pick up all the other DC negatives I need for drives ETC. . . . I do the same for DC positive as well.

    All shielded cables should only be earthed at one end and that taken back to the main earth star point.

    Hope the rough sketch helps.?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	STAR.jpg 
Views:	1386 
Size:	83.9 KB 
ID:	6725  

  8. The Following User Says Thank You to JAZZCNC For This Useful Post:


  9. #7
    Earth loops are always trying to sneak in and act like shorted out transformers. For example, an AC electric motor has an earth connection that goes to it's casing and that casing connects to the machine body which has a seperate ground connection. That is an earth loop with some major magnetic field activity in one corner and current starts to flow. Not only does the motor earth wire heat up but so do any other loops in the system, especially if they pass through the machine body. The Volts may be low but the current can be enormous.

  10. The Following User Says Thank You to Robin Hewitt For This Useful Post:


  11. #8
    Quote Originally Posted by Robin Hewitt View Post
    Earth loops are always trying to sneak in and act like shorted out transformers. For example, an AC electric motor has an earth connection that goes to it's casing and that casing connects to the machine body which has a seperate ground connection.
    Yep it's possible but lets not confuse the poor bloke any more than need be Robin.!! . . . In the main If he sticks to the star grounding then he shouldn't have any issue's.

  12. The Following User Says Thank You to JAZZCNC For This Useful Post:


  13. #9
    The guys going to be confused if he stays around here much longer anyway

    Jazz got it with his description of earthing. If you follow that you should be ok. Your original drawing made me think that you were connecting directly to the ring final circuit.

  14. The Following User Says Thank You to Web Goblin For This Useful Post:


  15. #10
    To all that have helped me so far, many thanks, it as restored my faith in human nature. It's great to know strangers can help each other.

    Best Regards

    Ray

Page 1 of 7 123 ... LastLast

Similar Threads

  1. Laser Machine Grounding/Earthing
    By Want2build1 in forum Laser Machines & Building
    Replies: 31
    Last Post: 09-02-2015, 10:18 PM

Bookmarks

Posting Permissions

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