Electrical shock-preventable key unit

Claim 1

An electric shock-preventable key unit comprising: a case formed of an electrically insulating material and having a longitudinally extending chamber therein; a longitudinally extending slot formed in said case; an aperture formed at one end of said case; a slide plate slidably disposed within said chamber and having a projection engaged with and protruded from said slot, so that said slide plate can be longitudinally slid between first and second positions by moving said projection along said slot, said slide plate being formed of an electrically insulating material; a key body formed of an electrically conductive material and having a grip portion secured to said slide plate and a key portion extending from said grip portion, so that said key portion is extended out of said chamber through said aperture when said slide plate is located in said first position and retracted therefrom when said slide plate is located in said second position; an electrically conductive member having a portion exposed on the surface of said case; an electrically conductive contacting member provided in said chamber at a position so that said contacting member is electrically contacted with said key grip portion when said slide plate is located in said first position; a resistor having both terminals electrically connected to said conductive member and said contacting member, respectively; and retaining means coacting with said slide plate to maintain said slide plate in said first position with said key portion extended from said chamber, said retaining means comprising a plate spring disposed on said case and having a portion for engagement with said slide plate, said engagement portion being shaped to provide a lower mechanical resistance to sliding movement of said slide plate to said first position from said second position and to provide a greater mechanical resistance to sliding movement of said slide plate to said second position from said first position.