What safety points should be considered when laying cables for explosion-proof video surveillance systems?

Explosion-proof video surveillance systems serve as the "visual defense line" in flammable and explosive environments such as chemical plants, mines, and oil and gas plants. Their stable operation directly impacts production safety and risk warning. Cables, as the core carriers of system signals and power transmission, pose a significant safety hazard during installation (such as seal failure or insulation damage). This can not only interrupt monitoring signals but also potentially become an ignition source, leading to major accidents such as fires and explosions. This article, considering the special requirements of explosion-proof environments, comprehensively outlines the key safety points of cable installation from five dimensions: cable selection, pre-installation preparation, installation process control, joint treatment, and post-installation protection, providing a scientific basis for engineering construction and maintenance.

I. Cable Selection: Building the "First Line of Defense" for Safe Installation

The cables for explosion-proof video surveillance systems differ from ordinary monitoring cables. They must simultaneously meet multiple requirements, including explosion-proof, corrosion-resistant, and interference-resistant properties. Incorrect selection can create safety hazards from the outset. Before installation, the following safety considerations should be prioritized:

(I) Explosion-proof rating and environmental compatibility

Different flammable and explosive environments require different explosion-proof ratings. The explosion-proof performance of cables must strictly correspond to the hazardous area classification on site. According to the GB 3836 series standards, hazardous areas are divided into Zone 0 (continuous presence of explosive gas mixtures), Zone 1 (possible occasional presence), and Zone 2 (possible temporary presence). Cables must be selected with corresponding explosion-proof ratings:

Zone 0 and Zone 1 environments: Intrinsically safe (Ex ia) or explosion-proof (Ex d) cables must be selected. Intrinsically safe cables limit current and voltage to ensure that even if the cable is damaged, no ignition energy will be generated; explosion-proof cables use special sheath materials and structures to prevent external explosive gases from entering the cable and causing an explosion.

Zone 2 environments: Increased safety (Ex e) cables can be selected. Their sheaths have certain dustproof and waterproof properties, reducing the impact of the external environment on the cables.

Special note: Ordinary surveillance cables (without explosion-proof certification) must never be used in explosion-proof areas. Even short-term installation may pose a danger due to insulation damage or electrical sparks generated during signal transmission.

(II) Cable Sheath Material Adaptation to Environmental Characteristics

Explosion-proof environments often involve corrosion, high temperatures, and mechanical wear. Therefore, the cable sheath material must be selected accordingly:

Chemical and oil/gas environments (including corrosive gases and liquids): Polytetrafluoroethylene (PTFE) or perfluoroalkoxy (PFA) sheathed cables are preferred. These materials are resistant to acids, alkalis, and organic solvents, and are less prone to aging and cracking over long-term use.

Underground mining environments (high humidity, dust, mechanical impact): Flame-retardant polyvinyl chloride (PVC) or neoprene rubber sheathed cables are selected. These materials possess flame-retardant, wear-resistant, and impact-resistant properties, and must meet coal mine safety standards (such as MT/T 818).

High-temperature environments (such as metallurgical workshops and boiler surroundings, temperatures >80℃): Silicone rubber (SiR) or fluororubber (FKM) sheathed cables are selected. These cables can withstand temperatures up to 150℃-200℃, preventing sheath melting and insulation failure due to high temperatures.

(III) Matching Cable Specifications with Transmission Requirements

Cable specifications must be determined based on the transmission distance and signal type (video signal, control signal, power) to avoid signal attenuation or overheating due to insufficient specifications:

Video signal transmission: If the transmission distance is ≤300 meters, use SYV-75-5 type coaxial cable (characteristic impedance 75Ω, low attenuation); if the distance is >300 meters, use shielded twisted-pair cable (such as CAT6 shielded twisted-pair cable) and a video balancer to reduce signal interference;

Power transmission: Calculate the cable cross-sectional area based on the camera power (usually 10W-30W) and transmission distance. For example, for 12V power transmission over 100 meters, use copper core cable with a cross-sectional area ≥1.5mm² to avoid excessive voltage drop due to insufficient wire diameter (the voltage at the end must not be lower than 10.8V), and to prevent cable overheating;

Control signal transmission (such as PTZ control, zoom signal): Use shielded RVVP type multi-core cable (such as RVVP... The shielding layer (2×0.75mm²) effectively resists electromagnetic interference in explosion-proof environments (such as electromagnetic fields generated by chemical equipment operation), ensuring stable control signals.

II. Pre-laying Preparations: Eliminating Potential Safety Hazards

Preparatory work before laying cables directly affects construction safety and subsequent stability. Three key tasks must be completed: environmental assessment, cable inspection, and tool preparation.

(I) On-site Environmental Safety Assessment

Before laying cables in explosion-proof areas, an environmental risk assessment must be conducted jointly with the safety management department to avoid triggering hazards during construction:

Hazardous Material Screening: Confirm the presence of explosive gases or dust in the laying area (e.g., combustible gas concentration needs to be tested in oil and gas workshops, and methane concentration needs to be tested in coal mines). Laying operations can only commence when the concentration is below 10% of the lower explosive limit.

Construction Space Planning: Avoid equipment operating areas, pipelines and valves (especially pipelines carrying flammable and explosive media), and high-temperature heat sources (e.g., reactors, furnaces). The cable laying path must maintain a distance of at least 0.5 meters from these hazardous sources to prevent cables from being baked by high temperatures or affected by equipment vibration.

Temporary Protective Measures: If temporary protective measures are required in Zone 1 or Zone 0... Construction in high-risk areas such as explosion-proof zones requires the establishment of temporary explosion-proof isolation zones, equipped with portable combustible gas detectors, fire extinguishers, and other emergency equipment. Construction personnel must wear anti-static work clothes and insulated gloves, and are strictly prohibited from bringing any source of ignition (such as lighters or mobile phones) into the site.

(II) Cable Quality and Integrity Inspection

Before laying, each roll of cable must be inspected section by section to eliminate any quality defects present at the time of manufacture:

Visual Inspection: Check for damage, scratches, or bulges in the cable sheath; ensure the shielding layer is intact (no exposed or broken parts); and ensure the markings are clear (including explosion-proof rating, specifications, manufacturer, and production date). If damage to the sheath is found, even if the insulation layer is not damaged, the cable must be replaced (no damage to cables is permitted in explosion-proof areas);

Conductivity and Insulation Test: Use a multimeter to measure the cable core... Measure the cable's continuity (ensuring no open circuits) using an insulation resistance tester (megohmmeter). The insulation resistance between the core wire and the shielding layer, and between the core wires themselves, should be ≥100MΩ at room temperature (≥500MΩ for intrinsically safe cables). If the insulation resistance is too low, it indicates that the cable insulation layer is damp or damaged, and the cable should not be used.

Check for explosion-proof certification: Obtain the cable's explosion-proof certificate (such as one issued by the National Explosion-proof Electrical Products Quality Supervision and Inspection Center). Verify that the explosion-proof rating and model on the certificate match the actual cable to avoid using substandard or counterfeit explosion-proof certified products.

(III) Preparation of Specialized Tools and Protective Equipment

Cable laying in explosion-proof areas requires the use of explosion-proof tools to prevent sparks from tool collisions. Necessary protective equipment must also be provided:

Explosion-proof Tools: Use explosion-proof wire strippers, screwdrivers, and wire cutters made of copper alloy. Ordinary steel tools are strictly prohibited (as they are prone to generating sparks upon impact). Tools must have explosion-proof certification markings. Before use, check tools for cracks and deformation.

Protective Equipment: Construction personnel must wear anti-static safety helmets, puncture-resistant work shoes, and insulated gloves. If corrosive media are present on site, chemical protective goggles and masks must be worn.

Auxiliary Equipment: Prepare explosion-proof cable laying racks (to prevent static electricity from friction during cable dragging), flame-retardant cable fixing clips (such as plastic clips specifically for explosion-proof areas; metal clips are prohibited for direct cable fixing to prevent scratching the sheath), and sealant (such as explosion-proof sealant putty and waterproof sealing rings).

III. Laying Process Control: Strict Adherence to Operational Safety Standards

The laying process is a core aspect of safety control. Appropriate laying methods must be selected based on the site environment (e.g., indoor, outdoor, underground), and operational standards must be strictly followed:

(I) Laying Method Selection and Safety Requirements

Different scenarios require different laying methods. The core principle is "avoiding cable exposure, reducing mechanical damage, and ensuring explosion-proof sealing":

Indoor explosion-proof areas (e.g., around the control room of a chemical workshop): Galvanized steel pipes should be used as the preferred method. Thick-walled steel pipes (wall thickness ≥ 2.5mm) must be selected. Explosion-proof unions (Ex d type) must be used for connections between steel pipes. Sealing tape and explosion-proof sealant must be applied to the joints to prevent explosive gases from entering the steel pipe. Steel pipe bends must be made using a bending tool, with a bending radius ≥ 6 times the diameter of the steel pipe. To avoid damage to the cable sheath caused by compression at bends in the steel pipe;

Outdoor explosion-proof areas (such as oil and gas storage tank areas, mine entrances): Cable trenches or direct burial should be used. Cable trenches must be covered (gaps in the cover should be sealed with explosion-proof sealant), and fine sand (≥100mm thick) should be laid inside the trench to prevent cables from being scratched by sharp stones. For direct burial, cables must be run through PE protective pipes (the pipe diameter must be at least 50% larger than the cable diameter), buried at a depth of ≥0.7 meters (below the frost line in frozen soil areas), with both ends of the protective pipe extending at least 0.3 meters above the ground and properly waterproofed (e.g., by installing waterproof bends);

Underground mines (humid, dusty, and confined spaces): Cable trays should be installed along the tunnel walls. Flame-retardant cable trays (compliant with MT/T 1097) must be used. (Standard specifications) Connections between cable trays must be secured with bolts. Cables must be laid in layers within the cable trays (power cables and signal cables must be laid separately, with a spacing of ≥100mm to avoid power interference with signals). The area beneath the cable trays must be kept away from mine car tracks, water pipes, and ventilation ducts to prevent cables from being damaged by mine car collisions or leaks.

(II) Safety Points for Cable Laying Operations

During the laying process, the cable dragging speed must be controlled to avoid excessive bending, and electrostatic discharge (ESD) protection must be implemented:

Control Laying Speed and Force: Cables must be dragged at a uniform speed, ≤5 meters/minute, to avoid rapid dragging that could cause static electricity to be generated due to friction between the cable and the ground or steel pipe (static electricity accumulation in explosion-proof areas may lead to explosions); if resistance is encountered during dragging, check for jamming (such as debris inside the steel pipe or blockage at the bend of the cable tray), and do not forcibly pull to prevent breakage of the cable core or damage to the sheath;

Avoid Excessive Bending: The bending radius of the cable must meet the specifications (bending radius of coaxial cable ≥ 15 times the cable diameter, twisted pair ≥ 10 times, power cable ≥ 20 times). If the bending radius is too small, it may cause the shielding layer to break and the insulation layer to be damaged, affecting explosion-proof performance and signal transmission;

Electrostatic Discharge Protection: Before laying, the cable, cable laying frame, and construction personnel must be grounded (using an anti-static grounding wire with a grounding resistance ≤ 4Ω) to release accumulated static electricity; every 50 meters of cable laid... The cable, measuring meters in length, must be temporarily suspended and its grounding resistance measured to ensure effective grounding and prevent electrostatic sparks from igniting explosive materials at the scene.

(III) Cable Fixing and Labeling Standards

Improper cable fixing can easily lead to mechanical damage, and unclear labeling can create safety hazards for later maintenance. The following points should be noted:

Fixing Spacing and Method: For cables laid in conduits, explosion-proof cable clips must be used to secure them at both ends of the conduit, at bends, and every 1.5 meters along straight sections. For cables laid in cable trays, clips should be used every 1 meter along straight sections and within 0.5 meters at bends. The clips must be compatible with the cable sheath material (e.g., plastic clips for PVC sheathed cables, metal clips with insulating pads for rubber sheathed cables). Do not directly bind cables with wire (wire can easily scratch the sheath and may generate eddy currents and heat).

Labeling: Explosion-proof labels should be affixed to both ends of the cable (camera end, video recorder end) and every 50 meters in the middle. The labels must include the cable's purpose (e.g., "video signal cable" "power cable"), specifications, explosion-proof rating, and laying date. The labels must be made of corrosion-resistant and high-temperature-resistant materials (e.g., stainless steel, PTFE) to avoid blurring due to environmental factors. IV. Joint Treatment: Preventing Explosion-Proof Seal Failure

Cable joints are a weak point in explosion-proof systems. Improper handling can allow explosive gases to enter the cable or equipment casing through the joint, potentially causing an explosion. Therefore, strict adherence to explosion-proof requirements is necessary:

(I) Explosion-Proof Requirements for Joint Fabrication

Joint fabrication must be completed in non-hazardous areas (such as explosion-proof control rooms). On-site fabrication of joints within explosion-proof areas is prohibited (unless pre-fabricated explosion-proof joints are used):

Core Wire Treatment: Explosion-proof wire strippers must be used when stripping the wire. The stripping length should be moderate (core wire exposed from the sheath ≤ 10mm) to avoid excessive stripping that exposes the core wire or insufficient stripping that results in poor contact. Core wire connections should use crimp terminals (copper cold-pressed terminals), and the crimping must be secure (using crimping pliers for 2-3 seconds). (Second time), twisting is prohibited (twisted joints are prone to excessive contact resistance, causing overheating and posing a danger);

Insulation and Shielding: After the core wires are connected, they must be wrapped with insulating heat shrink tubing (the heat shrink tubing must fully cover the exposed core wires after shrinking, extending at both ends into the sheath by ≥5mm). The shielding layer must be grounded separately (using copper braided tape connected to the grounding terminal, grounding resistance ≤4Ω). The shielding layer and core wires must not share a common ground (to avoid signal interference and poor grounding);

Explosion-proof Sealing: An explosion-proof junction box (explosion-proof rating consistent with the cable) must be used on the outside of the connector. The junction box must be filled with explosion-proof sealant (fill rate ≥90%). The sealant must be filled evenly, without air bubbles or gaps. The junction box cover must be bolted (bolt tightening torque must meet the manufacturer's requirements, usually 15-20 N·m) to prevent the sealant from falling off or the cover from loosening, which could lead to explosion-proof failure.

(II) Equipment Connector Connection Specifications

The connection between cables and explosion-proof cameras/video recorders must ensure the equipment casing is sealed:

Interface Matching: Select cables with the same interface specifications as the equipment (e.g., if the equipment interface is M20 thread, the cable must be equipped with an M20 explosion-proof gland). The gland must be tightened securely (after tightening, the sheath should not be loose, and there should be no gap between the gland and the equipment casing). Non-explosion-proof glands (such as ordinary plastic glands) are prohibited.

Sealing Treatment: A waterproof sealing ring (material compatible with the sheath) must be installed between the gland and the cable sheath. The sealing ring must fully enclose the cable without compression or deformation. Internal wiring terminals must be tightened (using a screwdriver, torque ≥ 5 N·m) to prevent vibration from causing loosening. After wiring, the equipment casing must be tightened as required (all bolts present, no missing or stripped bolts) to ensure the casing protection level reaches IP65 or higher (dustproof and waterproof).

V. Post-Launching Protection and Acceptance: Ensuring Long-Term Safe Operation

After cable laying is completed, post-laying protection and acceptance work must be carried out to promptly identify and rectify safety hazards:

(I) Post-Launching Protection Measures

Regular Inspection: Weekly inspection of cable appearance (whether the sheath is damaged and the markings are clear); monthly inspection of joint sealant aging and junction boxes loosening; quarterly measurement of cable insulation resistance and grounding resistance to ensure parameters meet requirements;

Environmental Protection: If the cable laying area contains corrosive media or high temperatures, regularly clean the cable surface of corrosive substances and dust (wipe with a dry cloth, do not wash with water). Install heat-insulating sleeves (such as fiberglass sleeves) on cables in high-temperature areas to prevent sheath aging;

Emergency Handling: If cable sheath damage is found, immediately stop the operation of the monitoring system in that area. Replace or repair the cable in a safe area (repair must use explosion-proof connectors; simply wrapping with insulating tape on-site is prohibited). After repair, the explosion-proof performance and insulation resistance must be retested. The cable can only be used again after passing the tests.

(II) Installation Acceptance Standards

The acceptance process must be jointly conducted by explosion-proof electrical professionals and safety management personnel, focusing on verifying the following:

Explosion-proof performance: Check whether the explosion-proof rating of the cable, explosion-proof joints, and sealing measures meet the requirements of the hazardous area on site.