Q. What are the requirements regarding ground detection systems and labeling for ungrounded systems?

A. Systems that aren't required to be grounded in accordance with 250.20(B) [250.21(A)(4)] must have ground detectors installed [250.21(B)(1)]. Thisground detection sensing equipment must be connected as close as practicable to where the system receives its supply [250.21(B)(2)]. In addition, ungrounded systems must be legibly marked "Ungrounded System" at the source or first disconnecting means of the system, with sufficient durability to withstand the environment involved [250.21(C)].