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AC/DC Voltage Grounding vs Bonding

  1. Aug 11, 2011 #1
    Good day to all,

    I'm a newbie to the site and I have a quick question for all you electrical geniuses out there. I will start of with a bit of insight into my question.

    I am a maintenance Controls Technician in the automotive industry who has some experience, in my earlier years, doing electrical design. So my question is as follows:

    Is it common practice to "ground," not bond, the common side of a DC power supply? I myself have only witnessed existing machines set up like this, never designed a circuit to be like this. My issues with this practice is that I was trained to never include both voltages on the same circuit. Also, if manufactures of said power supplies wanted this done why don't they include ground symbols/nomenclature or even internally jumper the 2 points as a common.

    I was also trained to "bond" all metal device together to avoid hazardous shocks due to stray current that has no where to go. I was also told "that's just common practice in all electrical circuits."

    If anyone has some insight in to this on going discussion I'm having with a co-worker would be appreciated.
  2. jcsd
  3. Aug 14, 2011 #2
    Most of the power supply have both terminals floating, you can ground either side to get + or - voltage output. So your question is really too general to give any comment or suggestion. Normally, we choose one potential as reference and we call it ground to which all power supply reference to. For example, if you want a +5V output, you tide the low side of the +5V supply to the common reference point ( Ground) and take the +ve side as +5V. If you need a -12V supply, you tide the +ve side of the 12V supply to ground and the -ve side become the -12V output. With this, you build the whole system.

    Remember system Ground ( the ground I described above) is not earth ground. There are cases that we actually put the reference ( the ground described above) onto the +ve output of a high voltage supply and the result is the whole system is being floated on top of the high voltage.

    In usual case, for safety, we take the system ground and tide it to the earth ground for safety reason so the system will not float up and down. It you leave the system ground floating, it might be charged up by simple static electricity and you can get a shot when you touch it. Even though it might not injure you, it can sure burn the electronics around. Don't think this is a simple subject, grounding is one of the difficult subject that you don't learn from school. A lot of noise issue, intermittent problems are due to improper grounding.
  4. Aug 14, 2011 #3
    Good morning Mdemmer, welcome to Physics Forums.

    Sometimes posts get missed, especially in the summer holiday period, so well done to Yungman for picking it up.

    To give the technique its full title, equipotential bonding is a process for interconnecting conductive (usually metal) material that is not part of any electric circuit. This material might be gas pipes, water pipes, metal balustrades, metal staircases, escalator metalwork, the casing of electrical apparatus and so on.

    In order to achieve this the earth is used as a constant voltage reference and current sink.

    This is done for two reasons.

    Firstly to avoid the possibility of one of these pieces of metal aquiring a potential difference in a fault condition and presenting a shock hazard to individuals.

    Secondly to avoid unwanted potential differences more generally leading to sparking and gas explosions or fire hazards.

    On the other hand one point in an electrical circuit is often connected to earth (or in american ground) to establish and hold steady a zero or reference potential, used by the whole circuit for circuit purposes.
    This is not essential and it not always done , it depends upon the circuit.

    When we do not make this connection the circuit (or the power supply) is said to be floating or isolated. There are many circuit situations in which we might wish to to do this so manufacturers of power supplies do not permanently tie a terminal to earth in order to give us the option.

    go well
  5. Aug 15, 2011 #4
    Thanks for the response.

    What was explained was what I needed. He was talking about an "Earth Ground" which I was always told is ONLY connected to the main panel for lightening reasons and so on. This earth Ground is sometimes a rod buried into the actual ground/soil. But I was also told that this style of grounding is only good for voltages around and above 600VAC (As the earth resistance can be too high for lower voltages) and is usually tied into the main disconnect for mean of a Ground Fault (IE; Line voltage short to ground)

    I also like the term equipotential bonding because this is what I was telling my co-worker he was talking about.

    Thanks Yungman and Studiot for your help
  6. Aug 15, 2011 #5
    I am no electrician, when I renovated my house, the contractor pounded a 6' copper rod into the ground and use it as earth ground. Power company don't seems to provide ground to the household. Power comes into the house as two of the three phase and the neutral so if you take the two phase, you get 220V, if you take one of the two phase and the neutral, you get 110V. The ground only come from a rod into the ground!!! Sorry if I am wrong, that was my observation.
  7. Aug 16, 2011 #6
    Yungman, I'm really enjoying reading your posts. I'm much like yourself (or so I think), in that I'm not an electrician but it's something I'm trying to learn all the time how to do and do well.

    Now I'm headed to wikipedia to learn about equipotential bonding!
  8. Aug 16, 2011 #7
    Thanks, electronics has always been my passion for the last 30 years even it was my career. Now that I am not working, I still spend two to three hours a day studying EM, antenna, math etc. At least I like it a whole lot more than playing cross word puzzle!!!:rofl:
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