Reclosers are small circuit breakers located at the top of distribution poles and are typically used on very long distribution feeders. Their function is to isolate a section of the feeder in fault or overload conditions and thereby minimize the number of customers without service. Since they act as small circuit breakers, they have the capability to restore power automatically in temporary fault situations, hence the name "recloser".
To further reduce the number of customers taken out of service in a fault condition, reclosers are "coordinated" with downstream fused cutouts and upstream substation circuit breakers. For example, let's say a tree branch falls across a tapped single phase line in a residential community. Without a recloser between the fused cutout serving the tapped single phase line and the substation circuit breaker, the entire feeder would be affected. With a recloser present, only that portion of the feeder downstream from it would be affected. Now, the recloser would operate (or open) and then reclose almost instantaneously. If the fault (tree branch on the line) is still present, the recloser would open again. This time it may be pre-set to wait a second or two before reclosing. After reclosing, if the fault is still there and the fused cutout didn't blow during the last operation, the recloser would hold for a short while to give the fused cutout time to blow and isolate just the tapped single phase line. If it doesn't for some reason, the recloser would open a third time and "lockout". At this point a lineman must be dispatched to inspect the problem and reclose the recloser manually.