Abstract: In the 1271 140 V power supply system, the artificial grounding to have the cover open power shut off has been applied to the major mine switches in Ch ina.An overvoltage grounding would be caused during the cover open power off transition process and under the condition of the action sensitivity lost.When over two s ets of the switches to be opened at the same time, there would be a grounding overvoltage over 30 mA safe current occurred. Some switches would be shut off only whe n the fastened bolt of the cover released (the flameproof function lost) .Those all would be the important dangers.Therefore it proposed that the mine intrinsic safe cove r sensor should be locked on the cover fastened bolt of the electric equipment and the connection point of the sensor should be linked with mine safety protection monit oring and control system (return circuit) .Before the cover to be opened, the lock should be firstly opened, the power would be secondly shut off, then the fastened bolt could be released and the cover could be opened. This method could be applied to all kind home and abroad electric equipment in the underground mine to have the ad vance cover open power off in order to eliminate above dangers.