LIGHTNING ARRESTER

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 a fuse or cut- out fuse (often referred to as a cutout) is a combination of a fuse and a switch, used in primary overhead feeder lines and taps to protect transformer from current surges and overloads. An overcurrent caused by a fault in the transformer or customer circuit will cause the fuse to melt and the switch mechanism to visibly open, disconnecting the transformer from the line. 

The cutout body, an open frame that supports the fuse holder and a ribbed porcelain or polymer insulator that electrically isolates the conductive portions of the assembly from the support to which the insulator is fastened.

The fuse holder, also called the "fuse tube" or "door", an insulating tube which contains the replaceable fuse element. When the contained fuse melts ("blows"), it opens the circuit, and the fuse holder drops out of the upper contact and hangs from a hinge on its lower end. This hanging fuse holder provides a visible indication that the fuse has operated and assurance that the circuit is open. The circuit can also be opened manually by pulling out the fuse holder using a hot stick. The fuse holder is typically made out of a fiberglass tube with a covering and metal contact points. As a fuse holder ages, the coating on the fiberglass will degrade and the fiberglass tube will start "shedding". The tube starts out with a pinkish hue then becomes white and then starts to "shed" fiberglass.

The fuse element, or "fuse link", is the replaceable portion of the assembly that melts and breaks the circuit when the electric current through it exceeds its rated current value. There are many types of fuse elements for many different uses such as a type T fuse also known as a "slow-blow fuse" being used for sidelines.

The fuse holder may be replaced by a solid blade, which would allow the fuse holder assembly to be used as a switch only.