Is it ok to connect common/ground of a dual supply to earth ground?

Discussion in 'General Electronics Chat' started by iinself, Dec 14, 2015.

  1. iinself

    Thread Starter Member

    Jan 18, 2013
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    Hi,
    please bear with me - just want to be sure?
    In the figure below is the connection in the red box OK? Can I connect the common of the dual supply to the earth ground?

    Also can I connect the speaker ground to this same point?

    Thanks

    psw-f1.png
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Yes, but is there some reason you think you want to do it?
     
  3. iinself

    Thread Starter Member

    Jan 18, 2013
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    For safety reasons - I have +/- 45V dc after the rectifier.
    The other reason was to eliminate any hum due to ground loops.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    Hum elimination is a good reason. What are you powering with this circuit? Have you tried isolating the source of the hum and trying to filter the source?
     
  5. iinself

    Thread Starter Member

    Jan 18, 2013
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    I am powering a class AB discrete amp. The question I have is by connecting the common to earth aren't we actually creating more chances of a shock. Since if we did not connect the common to ground and someone came in contact with the +ve or -ve lead of PSU there will be no shock unless he/she also touched the common. But with the common now connected to chassis because of earth ground; if someone touches the +ve or -ve lead and touch the chassis (which is far more probable compared to touching the common terminal) aren't they in for a shock (pardon the pun). I am almost sure I am wrong but I can't seem to explain myself.
     
    Last edited: Dec 15, 2015
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    If the AC power supply is galvanically isolated (transformer-coupled), it is ok to connect any single node in the down-stream circuit to earth ;)
     
  7. dl324

    Distinguished Member

    Mar 30, 2015
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    Using earth ground provides a low resistance path for current to flow in the event of a short of a "high" voltage to the chassis. Without the case being grounded, someone touching the case could provide the shortest resistance to earth ground. 35-45V is not a dangerously high voltage under most conditions.

    Using earth ground could solve your hum problem or make it worse. A better solution would be to isolate the source of the hum and address it; by removing ground loops and/or filtering the hum.
     
  8. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    No, assuming the wall outlet is wired correctly. In fact, connecting the secondary ground point to earth ground is a requirement for an SELV (Save Extra Low Voltage) output. Pretty much mandatory in medical equipment.
     
  9. iinself

    Thread Starter Member

    Jan 18, 2013
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    Thanks
     
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