what really is an ungrounded system?

Discussion in 'General Electronics Chat' started by unsaint32, Feb 28, 2005.

  1. unsaint32

    Thread Starter Member

    Jan 13, 2004
    14
    0
    Q 1) What is the purpose of ungrounded system. Is it not to trip the circuit breaker when

    the first fault occurs? (for more controlled deactivation?)

    Q 2) In a grounded system, having one conductor connected to earth provides the reference

    for steady voltages supplied to loads. How is stable voltage accomplished in an ungrounded

    system?

    Q 3) Actually, there is no such thing as an ungrounded system, right? (Because an ungrounded

    system is capacitively grounded.. whatever that means)


    Thanks for your answers

    Sung Hwang
     
  2. n9xv

    Senior Member

    Jan 18, 2005
    329
    1
    Where are you coming accross and ungrounded system? Can you give an example of such system.
     
  3. pebe

    AAC Fanatic!

    Oct 11, 2004
    628
    3
    Q 1. One use of an ungrounded system is safety. Now that may sound surprising but for anyone working on equipment at mains voltages it is essential. It is a requirement in the UK that electrical repair workshops and people using mains equipment on building sites must have electrical isolation between the mains supply and the user equipment. In the case of building workers the supply needs to be 120v max for safety.

    The secondary winding of the isolating transformer is always left 'floating', ie. ungrounded. If the operator then gets connected to one of the poles, no injury will result because there is no path through which current can flow. If one pole had been grounded and the operator touched the other pole, then assuming he was in contact with the ground, he would receive the full voltage across his body with possible fatal results. True, there will be a small capacity between the secondary winding and ground, but this will be minimal and present a high impedance to any current flow.

    Q 2. Whether the supply is grounded or not will make no difference to the provision of a steady voltage to the load. That is determined by the source impedance of the supply. The voltage is provided between the wires which deliver the supply, not by any grounding arrangements.

    Q 3. Strictly speaking you are right and there is always some degree of capacitive coupling to ground, but it can be so small as to be insignificant.

    Consider standing under a high voltage pylon where the wires are at half a megavolt to ground. There is some capacitive coupling between the wires and you, but it is so small you would never feel the effect.

    Hope that clarifies things
     
  4. n9xv

    Senior Member

    Jan 18, 2005
    329
    1
    That reminds me of a story of a guy (I think in Texas) that built a coil assembly of some sort and was actually using the "coupling" effect to generate enough voltage/current to run his home. The power company indicated an unexplainable power consumtion on the system but did'nt know why! I think he eventually got caught.
     
  5. Erin G.

    Senior Member

    Mar 3, 2005
    167
    1
    In addition to other responses, ungrounded systems are also found on ships at sea. Since there is no reference to "earth ground", there is no true ground. A typical house or building wiring system will have a hot, neutral and ground: On board a ship you will have two hots, and a ground- but the "ground" is really the ship's hull. If you were checking voltage on a 120VAC circuit on a ship, you would find 55 volts between each hot and the "ground".
     
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