Explosion-proof design features

A shell design
Portable, intrinsically safe instrument shell plastic case is sometimes used, sometimes with metal casing. Elected with a plastic shell, in order to ensure the normal operation without plastic shell accumulate hazardous static electricity, the surface resistivity not exceeding 1 × 109Ω. After impact plastic housing should test and thermal stability test.
Normal operation sparks, arcs or dangerous temperature electrical equipment, power greater than 250W or greater than 5 A current class Ⅰ electrical equipment shall be used with the device body circuit breakers boxes for electrical junction box is designed for cable or wire and electrical equipment connected components. Currently class Ⅰ flameproof electrical equipment is widely used flameproof wiring. Box junction box wall should be painted arc-resistant paint, junction boxes and the body cavity should be done on the flameproof joints rust treatment, such as coated rust oil.
In addition, for explosion-proof electrical appliances, which you want to have a prominent place on the  Electric energy meter  signs and MA total Ex-safety signs.
Some parts of the coal mine for the presence of illegal operation of a motor phenomenon, we developed a small explosion-proof type QF40 starter, the rated voltage 380V, rated current of 40A. Shell design into the body cavity and wiring cavity. Case of 3 mm thick steel plate. Flameproof joints the size and precision meet GB3836.2 requirements. Case dimensions of 437 mm × 308 mm, shell protection grade IP54. In front of the enclosure has a nameplate with Ex symbol top right corner, proof mark d Ⅰ (150 ℃), In addition, there are also marked on the nameplate name, model, rated voltage, rated current, proof certificate number, safety signs, serial number, date of manufacture, etc.
2 circuit design
First, the electrical circuit is designed to complete the electrical function to ensure the accuracy of the electrical theory. Secondly, explosion-proof electrical clearances, creepage distances, insulation parameters must meet the requirements of GB3836 requirements. For example, the development of QF40-proof starter, it will be designed terminal creepage distance of not less than 16 mm, clearance of not less than 10 mm. Explosion-proof electrical components and assembly cavity arrangement creepage distance not less than 16 mm, clearance of not less than 10 mm. Flameproof terminal compartment with internal grounding screw. Case has external ground screw.
Developed intrinsically safe steel strings frequency meter in normal operation and fault conditions the maximum operating current and voltage are not greater than the maximum allowable current design: it is creepage distance of 3 mm, the insulating coating under the creepage distance of 1mm , clearances of 3 mm.
3 power supply design
Intrinsically safe portable Voltage stabilizer  equipment independent power is the most commonly used batteries and accumulators. Batteries and battery power are all resistive circuit, according to the resistive circuit power curve to determine the minimum ignition current security parameters. Maximum battery voltage detected by the corresponding minimum ignition current, and then divided by the safety factor values ​​(2), namely that the battery design allows for maximum safety. Most severe state of discharging the battery is shorted directly to the battery. Therefore, the maximum short-circuit current to battery power as a measure of intrinsic safety benchmarks. If the battery is designed to allow the maximum short-circuit current is greater than the value, you must add the current limiting resistor string. Also, the battery or the battery and the current limiting resistor glue labeled one, constitutes intrinsically safe components. Rubber seal materials are epoxy, silicone rubber, industrial paraffin, etc.