The correct answer is C) Accidental contact between one line and ground does not cause an outage. In an ungrounded electrical distribution system, there is no direct connection between the circuit and ground. This means that a single ground fault, where one line accidentally contacts ground, will not cause an outage. The system can continue to operate, as the fault is not completed through the ground. This is a key characteristic of an ungrounded system. The other answer choices are incorrect because: A) In an ungrounded system, a single ground fault does not cause an outage; B) Double ground faults can cause an outage by completing the circuit through the ground; and D) Ground detection systems are actually necessary in ungrounded systems to monitor for single ground faults.