Line Fuses/Cutouts/Oil Switches
There are a variety of fuses and switches used on the distribution system to provide greater reliability, flexibility, and control of the system. Line fuses, cutouts, and oil switches are common devices that protect the system and provide a means to de-energize only a portion or section of a line for maintenance or repair.
A line fuse is simply a fuse the electricity travels through on the line. Line fuses are placed wherever a feeder taps off a main distribution line. If there is an overload or short circuit on the tapped line, it will blow the line fuse at the point where the tap occurs instead of tripping the substation breaker and shutting off power to everyone on the circuit. Only the customers served off the tap line are without power.
One of the most common switching and control devices is the "cutout". It is a simple single-pole, high voltage switch with one hinge point and one contact point that is opened and closed using a long insulated pole with a hook on the end called a "hook-stick".
A cutout can also contain a separate fuse in which case it is called a fused cutout. Fused cutouts are fused switches that sectionalize a segment of a tap line from the distribution line, or protect a distribution line from short-circuits or overloads. Therefore, a fused cutout serves as both a disconnect switch as well as a low voltage protective device.
Oil switches are load break switches with the contacts immersed in oil inside a small steel can. They can be either manually or electrically operated through an outside remote control device or circuit. Electrically controlled oil switches are opened and closed by a solenoid mechanism which operates very quickly. The fast operation insures virtually simultaneous operation when a bank of three are used for load break switching on a three-phase line.