Lightning arrester

In telegraphy and telephony, a lightning arrester is placed where wires enter a structure, preventing damage to electronic instruments within and ensuring the safety of individuals near them.

[United States-centric] A potential target for a lightning strike, such as an outdoor television antenna, is attached to the terminal labeled A in the photograph.

Ordinarily no current will flow between the antenna and the ground because there is extremely high resistance between B and C, and also between C and D. The voltage of a lightning strike, however, is many times higher than that needed to move electrons through the two air gaps.

Other designs of lightning arresters use a glow-discharge tube (essentially like a neon glow lamp) connected between the protected conductor and ground, or voltage-activated solid-state switches called varistors or MOVs.

Lightning arresters are rated by the peak current they can withstand, the amount of energy they can absorb, and the breakover voltage that they require to begin conduction.

Powerline worker performs maintenance of a lightning arrester on an electrical transmission tower in New Brunswick, Canada
Base of a mast radiator with spark gap and series inductance in form of a coil with one winding in the feeder line
The antenna is attached to A, and a pipe in the ground is attached to E. The television signal can go from A to B but not from B to C or from C to D. However, when the high voltage of lightning hits, it can easily go through the air from B to C and from C to D and E.