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	Subject - what really is ungrounded system? unsaint34 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, because an ungrounded system is capacitively grounded? (whatever that means) Thanks for your answers Sung Hwang Ryan_J 1) The purpose of an ungrounded system is just as you say...to not trip a breaker on the first fault. This holds true for a high impedance grounded system as well. 2) The connection to earth, in my opinion, does NOT stabalize the voltage, contrary to popular belief. This stability is provided by the system bonding jumper, which makes the ssytem a grounded system. Voltage stability is not present in an ungrounded system. Measuring voltage from phase to phase in an ungrounded system will give you anticipated results, such as 480. Measuring phase to ground, howver, will give unanticipated results, such as anywhere from 300-2200 volt! 3) Correct, all systems are "earthed" and therefore capacitvley coupled to ground. This connection, however, is of very high impedance, and therefore ground fault clearance does not occur until a second fault occurs. unsaint34 Ryan, thanks for the answer Onething I don't understand... you say the system bonding jumper makes the stable voltage, not the system's connection to earth. What the bonding jumper connects to the system is earth and noncurrent carrying enclosures. And since an ungrounded system doesn't have earth connected to the neutral conductor, are you saying that the equipment bonding makes stable voltage? Ryan_J Ungrounded systems will never have a stable voltage when measured phase to ground. What I meant when I was talking about voltage stability is for grounded systems. lucky1122 By tying the neutral conductor of an electrical system to ground what that does is several things . Firstly it stabilizes the voltage to ground by minimizing the voltage of the system to ground.If a ground fault occurs in a grounded system It will not exceed the voltage from any ungrounded conductor to the neutral conductor thus the voltage is stabilized not to exceed that level. It also brings that conductor to ground potential and insures that stray voltages that may be imposed on the system will be minimized . The most important function of grounding is that by placing the neutral at ground potential you are creating a path back through the system neutral or the grounded circuit conductor of the system to facilitate the opening of Overcurrent devices. this is accomplished through effective bonding . Remember this if I didnt tie the neutral of a single phase service to ground at the S.E. even though the transformer source at the pole is grounded to earth the impedance of the earth itself would be too high to facilitate the operation of the breakers during a fault. It is the bonding jumper between the equipment ground and the neutral that is the intended path for fault current. That is why the ungrounded system does not trip the breaker until the second fault occurs . When that happens the system becomes in effect grounded through the first fault,. hope that helps