Abstract: General industrial and mining enterprises of electrical equipment often adopts the over-current protection air switch to achieve the corresponding rated current, or a maximum supply generator, power distribution cabinet to achieve current limiting protection, these programs are not very flexible, not very safe. Design of a mining electrical equipment external flow alarm, using the current secondary measurement of main circuit of current transformer, two secondary induction current in series with a variable sampling resistance, if the main circuit current exceeds a predetermined (in electrical equipment to the premise of the work can be scheduled) current sampling resistor voltage light LED LED, photosensitive resistance was light, the resistance decreased dramatically, flip-flop outputs high level, cut off the main circuit power supply, and trigger multivibrator oscillation output square wave, achieve sound and light alarm. This design can be integrated into the power distribution cabinet circuit, more clever can be independently designed as a module, the alarm module in the premise of ensuring the normal work of the next load can be applied to almost all the electrical equipment system.