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KNIFE SWITCHES, 1940's
A selection of knife switches for general switching purposes.From the 1940's&50's
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Single pole lever switches switches were often used to protect wireless units from lightning damage, and were commonly seen on window ledges during the 1950's and before.
Normally the lever is thrown to connect the aerial, when the operator is finished the lever is changed over to the other side, which is connected to earth. A direct strike would not protect very much as the voltage would be high enough not only damage the aerial but also anything in the proximity of the wiring, however a near strike would send all received voltages to ground.
In the case of Sheet lightning whole areas can be ionised causing the atmosphere to glow blue in colour, such strikes are generally dissipated and without the switch being set to ground certain damage would occur.
On some of the switches there is a spark gap in the On position, so that if the switch is not in the earth position some of the voltage can jump the gap.