A fast mechanical switch of plane configuration with foil insulation is described. Its closure is ensured by an exploding aluminum foil. With 0.4 mm insulation and a 500 kA current rating the switching time is 2.4±0.17 μsec. An increase of the insulation thickness and of the current rating increases the delay, but in a wide range of parameters the jitter time remains practically constant. The switch has been successfully used for series and crowbar operation on a circuit having a voltage of 18 kV, a frequency of 25 to 50 kHz, and a current of several hundred kiloamperes. When the switch components are so assembled to suppress all air gaps in the vicinity of the exploding foil, the jitter time can be brought down to 0.07 μsec.