I. Introduction
Low voltage distribution boxes are the lowest level of control and protection equipment in the power system and represent the most fundamental component for ensuring safe power system operation. They have a high frequency of contact with workers, but due to their large quantity, wide distribution, and typically low value, they are often overlooked by equipment power departments. This results in many low voltage distribution boxes being in an uncontrolled state, leading to unsafe factors and increasing the risk of electric shock and electrical fires. Therefore, attention must be paid to the safe selection and use of low voltage distribution boxes.
II. Selection of Protection Types for Low Voltage Distribution Boxes
The protection type of low voltage distribution boxes should be selected based on the conditions of the workplace.
1. In areas with relatively low risk where relative humidity does not exceed 75%, and there is no dust, corrosive gases or vapors, or flammable or explosive materials, open-type low voltage distribution boxes may be selected.
2. In particularly damp areas with relative humidity approaching 100% and in areas with corrosive gases or vapors, protected-type distribution boxes should be selected.
3. In dusty areas where large amounts of dust are generated, dust-proof distribution boxes should be selected.
4. In H-1 and H-2 class fire hazard areas with flammable liquids, suspended or accumulated combustible dust, or combustible fibers, dust-proof distribution boxes should be selected; in H-3 class fire hazard areas with solid combustible materials, protected-type distribution boxes may be selected.
5. Selection for explosion hazard areas:
(1) In areas with gas or vapor explosive mixtures:
① In Q-1 class areas where explosive mixtures can form under normal conditions, flameproof, explosion-proof ventilated, or pressurized low voltage distribution boxes should be selected.
② In Q-2 class areas where explosive mixtures cannot form under normal conditions but can form under abnormal conditions, any type of explosion-proof distribution box may be selected.
③ In Q-3 class areas where explosive mixtures cannot form under normal conditions but can form under abnormal conditions with low probability, enclosed-type distribution boxes may be selected.
(2) In areas with dust or fiber explosive mixtures:
① In G-1 class areas where explosive mixtures can form under normal conditions, any class of flameproof, explosion-proof ventilated, or pressurized distribution boxes may be selected.
② In G-2 class areas where explosive mixtures cannot form under normal conditions but can form under abnormal conditions, dust-proof distribution boxes may be selected.
