Electrical equipment for generating sparks, arcs, or hazardous temperatures, Class I electrical equipment greater than 250W or current greater than 5 a, is required to use the junction box and the equipment body to electrically connect the junction box is the special cable or wire Electrical equipment for connection components. Currently, Isolated explosive electrical equipment is widely used in explosive wiring. The inner wall of the cartridge should be applied to the arm, the junction box, and the composite surface of the out-proof joint surface should be used as a rust-proof treatment, such as coating anti-rust oil. indoor heater First, the circuit design should complete the electrical function of the electric heater to ensure the correctness of the electrical principle. Second, the electrical gap of the explosion-proof electric heater, the crawler, and insulation parameters must meet the requirements of GB3836. For example, when the QF40 explosion-proof starter is developed, the creepage distance of the terminal block is not less than 16 mm, and the electrical gap is not less than 10 mm. The intermediate electric heater element and the assembly arrangement of the assembly arrangement are not less than 16 mm, and the electrical gap is not less than 10 mm. An inner ground bolt is provided in the explosion-proof junction chamber. The outer casing is provided with an external bolt. The essential safety steel string frequency gauge is not greater than the maximum allowable current of the design in normal operation and fault state: its creepage distance is 3 mm, and the climbing distance under the insulating coating is 1mm. The electrical gap is 3 mm. For the motor violation operation in some local coal mines, we have developed a QF40 type explosion-proof starter with rated voltages 380V, rated current 40A. The shell is designed to be a body cavity and a junction chamber. The outer casing is 3 mm thick steel plate. The size and processing accuracy of the separation joint surface meet the provisions of GB3836.2. The outer casing has a size of 437 mm × 308 mm, and the housing protection level is IP54. There is a nameplate in the front of the outer casing. There is an ex sign in the upper right corner of the nameplate. In addition, the nameplate is also marked with name, model, rated voltage, rated current, explosion-proof certificate number, safety mark. Factory number, manufacturing date, etc. The most commonly used independent power supply of electric heater is a dry battery and a battery. Both drying batteries and battery power are resistive circuitry, which can determine the power security parameters at the minimum ignition current curve of the resistive circuit. Pressing the highest voltage of the battery to find the minimum ignition current, and then divide the safety factor (2), which is the design of the battery to allow maximum safety current. The most severe discharge state of the battery is the battery direct short circuit. Therefore, it should be based on the maximum short circuit current of the battery as a baseline that measures the intrinsic safety performance of the power source. If the maximum short circuit current of the battery is greater than the design allowable value, the limit current resistor must be serialized. Also, the battery or battery is sealed with a current limiting resistor, which constitutes an intrinsically safe assembly. The rubber sealing material has epoxy resin, silicone rubber, industrial stone wax, etc.