If the limb is clear, the power will stay on. If the limb is still there the power will turn off again for two seconds. Depending on the exact location in the system, if the fault stays on the line through three cycles or four cycles, the power is permanently turned off and a repair crew must come, clear the fault, and re-energize the circuit. A squirrel or other animal has been electrocuted and the system has isolated the short circuit. A lightning stroke has operated a lightning arrestor, resulting in a temporary fault that has been isolated by the arrestor.
Trees are one of the major enemies of the electric system.
Tree limbs can cause short circuits by simply brushing against lines. During snow or ice emergencies, the limbs can interrupt power to thousands of customers. TUB tries very hard to strike a balance between system reliability and the aesthetic qualities of the community. This is a loosing battle. Frankly, on a clear sunny day, any trimming is too much.