Then there is the interlock found on equipment with high (a.k.a. 'deadly') voltage inside, like a broadcast transmitter.
Usually it is a series string of micro-switches that are closed when the access panel is in place.
To prevent residual voltages from killing someone, manufacturers devised ways to immediately take the High Voltage supplies to ground when the series-string was opened.
Typically, this is a honking big solenoid which is pulled in when the series string is complete, and drops out, usually assisted by gravity, to short a pair of terminals that ground the H.V. supply.
Older equipment, however, usually employed the kind of micro-switch that was closed in two positions..one when the plunger was pushed in against a spring, and the other (when it was necessary to troubleshoot with the door or panel off) by PULLING out on the plunger.
But the advent of 'solid-state transmitters; has changed all that:
The first generation of 'solid-state' transmitters were voltage-limited to around 50-60 volts, at correspondingly high amperages to get the required power....The Harris MW-1, the first AM of that type, ran 53 volts at 23 amps for 1000 watts. Then there was a jump to about 120 volts, the Gates 'Five' series runs 106 volts @ 56 amps for 5000 watts.
Now with higher-rated solid-state devices, voltages are creeping back up, 300 volts seems to be the new 'norm'.
Scariest thing I ever saw was the meter for the High Voltage on a Harris MW-50, 50,000 watt AM...........0-30 KV.
Hope I didn't bore anyone with this.....I generally just read to pick up useful information about 'supply side of the meter' since I maintain numerous broadcast sites, from 1000 W AM's to 20 KW FM's.
Regards to all and thanks for all the education.
Gary