The following are the specifications for the inlet and outlet lines of explosion-proof distribution boxes:
Wiring methods
Generally, explosion-proof steel pipe wiring and cable wiring are used. Thick-walled pipes should be used as much as possible, and some may need to be subjected to pressure tests.
When cable wiring is used, overhead lines of 10kV and below shall not cross the explosion-hazardous environment; when the overhead line is adjacent to the explosion-hazardous environment, the distance between them shall not be less than 1.5 times the height of the tower.
Inlet and outlet line positions
The inlet and outlet ports should be located on the lower bottom surface of the box body, and should be avoided as much as possible on the upper top surface, side, back or door of the box body.
For some distribution boxes with special requirements or designs, such as top-in and top-out, top-in and bottom-out, etc., it is necessary to ensure good sealing, such as regular inspection and tightening of the compression nut, and secondary sealing with explosion-proof cement.
Wire selection
The wire with a suitable cross-section should be selected according to the rated current of the distribution box, the use environment and other factors. The allowable current carrying capacity of the conductor shall not be less than 1.25 times the rated current of the fuse element and the rated current of the long-delay overcurrent release of the circuit breaker.
In the explosion-proof enclosure with an explosion-proof environment hazard level of 2, the power supply line shall use aluminum core wires or cables with a cross-section of 4mm² or more, and the lighting line may use a cross-section of 2.5mm²; in the explosion-proof environment hazard level 1 zone, the distribution line shall use copper core wires or cables.
For places with large vibrations, multi-strand copper core soft wires or multi-strand copper core cables should be selected.
Line laying
The line should be laid in a location with low explosion hazard or far away from the release source, and should be laid along the outer wall of a building with explosion hazard.
When the explosion-hazardous gas or vapor is heavier than air, the line should be laid at a high place, and the cable should be directly buried or laid in a cable trench filled with sand; when the explosion-hazardous gas or vapor is lighter than air, the line should be laid at a low place, and the cable should be laid in a cable trench.
Wire connection
The connecting wires in the box should be insulated wires, and the joints must be firm without exposed live parts.
The working neutral wires in the distribution box and the distribution box should be connected through the terminal board.
When selecting aluminum core cables or wires, there must be a reliable intermediate joint for the electrical circuit in zone 1 in the explosion-proof box, and the intermediate joint for the electrical circuit in zone 2 must be located in the explosion-proof junction box or in a junction box close to the hazardous environment.
Grounding requirements
The metal shell of the explosion-proof distribution box should be equipped with an external grounding terminal, and the junction box should be equipped with a grounding terminal. The grounding parts should be rust-proof or made of rust-proof materials.
The protective grounding resistance should be less than 4Ω, and the working grounding resistance should be less than 1Ω.
The grounding wire should be as short as possible to reduce the grounding resistance and electromagnetic interference; it should be as far away from the explosion hazard area as possible to prevent sparks or electromagnetic ignition; and it should have good electrical connections to ensure that the electrical equipment can be quickly grounded in the event of a fault.
Sealing requirements
The incoming and outgoing cables pass through the rubber sealing ring and are compressed with washers and compression nuts to ensure the sealing performance of the flameproof shell. The cables must not be loose.
Unused inlet and outlet ports must be sealed with sealing gaskets and metal gaskets.
Marking and protection
The wires should be clearly marked to ensure that the terminals and wiring are firm and easy to maintain and repair.
It is strictly forbidden to connect the power cord entering the switch box with a plug.
The inlet and outlet cables should be sheathed and bundled and waterproofed. The wire bundles must not be in direct contact with the inlet and outlet of the box.
