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	Subject - article 250.4 (B) (2) unsaint34 A quote from 250.4 (B)UNGROUNDED SYSTEM (2) , "[equipment bonding] shall be connected together and to the supply system grounded equipment." Does the "supply system grounded equipment" indicate that the supply system is system-grounded? Or does that just mean that the suuply system's equipment bonding is connected to earth? (because an ungrounded system's equipment bonding gets connected to earth, but not to the power source) kbsparky It's my understanding that all the enclosures, conduits, and such need to be bonded together, and connected to "earth" for lightning protection, as well as minimize the potential to personnel who may come in contact with said equipment, under fault conditions. I believe that ungrounded systems are used in industrial applications where unscheduled shutdown of equipment can cause great inconvenience as well as financial loss. Phase monitors are supposedly in place to ensure that once a fault has occured, the equipment can be shut down in an orderly manner for the repairs to be performed. Of course, if a 2nd fault occurs (on a different phase) before said repairs could be made, that condition usually shuts it down anyways Ryan_J It also gets connected to earth so that fault current can travel through the earth and back to the transformer. Because the earth has such great impedance, it greatly decreases the fault current (to less than 5 amps or so). When this happens the ground detector alarm goes off, like sparky was saying above. Interesting thought: Ungrounded systems have been around for nearly 100 years, yet the 2005 NEC is the first edition to require ground detectors!