Comprehensive Guide to Determining Cable Parameters for Explosion-Proof Electrical Equipment

II. Precautions for Determining Key Cable Parameters 1. Determination of the conductor cross-sectional area – The dual challenges of \"current-carrying capacity\" and \"voltage drop\" This is the most crucial parameter, and it must meet two requirements simultaneously: Precaution 1: Correction for current-carrying capacity based on ambient temperature. Key point: The current-carrying capacity of a cable is not a fixed value; it depends heavily on the ambient temperature. Hazardous area scenarios: The ambient temperature in areas prone to explosions can be very high (such as in areas exposed to direct sunlight outdoors or near high-temperature equipment). The current-carrying capacity at the standard ambient temperature must be corrected downward using the correction factors specified in the \"GB 50217-2018 Code for Design of Cables in Electrical Engineering\". Safe practice: The corrected allowable current-carrying capacity of the selected cable cross-sectional area must be greater than the maximum continuous operating current of the circuit, with a certain margin left. Note 2: Verification of voltage drop. Key point: For circuits with long-distance power supply, it is necessary to verify the voltage drop. Hazard: Excessive voltage drop can result in too low a voltage at the equipment, preventing the motor from starting or causing it to deliver insufficient power, which in turn leads to abnormal operation of the control equipment. For the motor circuit, the voltage drop from the transformer to the motor terminals is typically required to be no more than 5% ； The lighting circuit should be no more than 3%. Calculation method: Calculated based on circuit current, cable length, cross-sectional area, and conductor material. If the voltage drop exceeds the limit, it is necessary to increase the cable cross-sectional area, rather than simply raising the output voltage. 2. Selection of cable insulation level (rated voltage) – “Withstand voltage” is the basis. Note: The rated voltage U₀/U of the cable must be greater than or equal to the rated voltage of the system. U₀: Voltage of the conductor with respect to ground. U: Voltage between conductors. For example, in a 0.6/1kV system, cables with a rated voltage of 0.6/1kV or higher must be selected. Cables of 450/750V must never be used in 380V power systems. 3. Selection of cable insulation and sheath materials – “halogen-free, low-smoke, flame-retardant” is the mainstream approach. In enclosed spaces with dense populations or valuable equipment, the burning properties of cables are of critical importance. Recommended type: Preferably choose WDZ- (halogen-free, low-smoke, flame-retardant) series cables. Halogen-free (W): Does not release corrosive or toxic halogen acid gases during combustion, protecting personnel and equipment. Low smoke (D): Low smoke density and high light transmittance during combustion, facilitating evacuation of people and firefighting operations. Flame Retardancy (Z): The ability to suppress the spread of flames. Common models: WDZ-YJY (cross-linked polyethylene insulation), WDZ-KYJY (control cable), etc. 4. Selection of cable protection and shielding structures – “Mechanical protection” and “Signal integrity”. Mechanical protection: Armored cables (such as YJV22, KVV22): When the cable is buried directly or may be subjected to significant mechanical stress in trays/pipes, cables with steel tape or steel wire armor should be chosen to provide resistance to compression and damage by rodents. Unarmored cables: Used in fixed installations where there is no risk of mechanical damage. Shielding: Power cables: Generally, shielding is not required. Cables for instrumentation and control systems: Total shielding or twisted-pair shielding (such as KVVP, DJYPVP) must be used to prevent electromagnetic interference and ensure stable and accurate signal transmission. This is particularly important for intrinsically safe circuits. 5. Determination of the cable outer diameter – the key to “sealing”. This parameter directly influences the selection of the explosion-proof connection fitting (flange), and it constitutes the physical basis for ensuring explosion-proof sealing. Note: During the cable selection phase, it is necessary to initially determine the outer diameter range of the cable. Select an explosion-proof flange that matches precisely based on this outer diameter. Each GRAN head has its applicable cable outer diameter range. It is strictly prohibited for the outer diameter of the cable to be less than the minimum value allowed by the gland; otherwise, effective sealing and clamping cannot be achieved. It is recommended that the actual outer diameter of the cable be in the upper middle range of the allowable range for the gland, to achieve optimal sealing and clamping performance.

III. Special requirements for special systems 1. Additional requirements for cables in intrinsically safe systems (E*) Distributed parameter limitations: In long-distance intrinsically safe circuits, the distributed inductance (L) and distributed capacitance (C) of the cables can store energy, thereby potentially compromising their \"intrinsically safe\" properties. Precautions: It is necessary to verify the L/R ratio and C value of the cable to ensure that the energy accumulated throughout the circuit does not exceed the safety limits. It is usually necessary to consult the inductance and capacitance values per unit length provided by the cable manufacturer for calculations. 2. Cross-sectional area of the grounding conductor (PE wire) Note: The cross-sectional area of the protective grounding wire must meet the requirements of GB 50303-2015. When the cross-sectional area of the phase wire S ≤ 16 mm², the ground wire should have the same cross-sectional area as the phase wire. When 16mm² < S ≤ 35mm², the ground wire should be at least 16mm². When S > 35mm², the minimum ground wire size is S/2. IV. Relevant Standards and Regulatory Basis: The determination of all parameters must be based on established guidelines: \"GB 50217-2018 Code for Design of Cables in Electrical Engineering\": the fundamental standard for cable selection. GB 3836.15-2017 Explosive atmospheres – Part 15: Design, selection and installation of electrical equipment: It establishes mandatory requirements regarding the types of cables, their installation, introduction, and grounding in areas prone to explosions. \"GB 50303-2015 Code for Acceptance of Construction Quality of Building Electrical Engineering\": It sets out specific requirements for the installation, wiring, and grounding of cables. Conclusion Determining the cable parameters of explosion-proof electrical equipment is a delicate task that requires foresight and systematic thinking. It requires designers to: calculate accurately: precisely compute the current capacity, voltage drop, and intrinsically safe parameters. Right choice: Select the appropriate cable material and structure based on the environment. Think of everything: Consider in advance the compatibility between the cable’s outer diameter and the explosion-proof sealing interface. In summary, a qualified cable must meet all standards in four aspects: electrical performance, mechanical performance, environmental adaptability, and explosion-proof interfaces. Only in this way can this “lifeline” truly provide safe and reliable protection for equipment and personnel in explosive hazard environments. Any oversight at any stage can render all the previous careful explosion-proof design efforts futile.

【Ten Years of Rapid Development in Chemical Equipment】2791-2025: Fuda Zijin Hydrogen Energy unveils China’s first 1,000-kilogram-class commercial ammonia decomposition hydrogen production and hydrogen refueling station https://bbs.hcbbs.com/thread-5704209-1-1.html (Source: Haichuan Chemical Industry Forum)

【Ten Years of Rapid Development in Chemical Equipment】By 2025, Sinochem Advanced Fibers’ technology for producing para-aramid will reach international advanced levels. https://bbs.hcbbs.com/thread-5704132-1-1.html (Source: Haichuan Chemical Industry Forum)

【Ten Years of Rapid Development in Chemical Equipment】2788-2025: Breaking Free from Import Dependence! 140,000 tons per year production capacity for ultra-high purity high molecular weight polyethylene launched in Shanghai! https://bbs.hcbbs.com/thread-5704112-1-1.html (Source: Haichuan Chemical Industry Forum)

【History of Haichuan Chemical】Born for the defense chemical industry, Hualu Engineering Company has achieved remarkable development over 60 years https://bbs.hcbbs.com/thread-5704223-1-1.html (Source: Haichuan Chemical Forum)

【Ten Years of Rapid Development in Chemical Equipment】2791-2025: Fuda Zijin Hydrogen Energy unveils China’s first 1,000-kilogram-class commercial ammonia decomposition hydrogen production and hydrogen refueling station https://bbs.hcbbs.com/thread-5704209-1-1.html (Source: Haichuan Chemical Industry Forum)

【Ten Years of Rapid Development in Chemical Equipment】2791-2025: Fuda Zijin Hydrogen Energy unveils China’s first 1,000-kilogram-class commercial ammonia decomposition hydrogen production and hydrogen refueling station https://bbs.hcbbs.com/thread-5704209-1-1.html (Source: Haichuan Chemical Industry Forum)

【Ten Years of Rapid Development in Chemical Equipment】2792-2025: Breaking Monopolies! Huayou Gongjian Company’s self-developed \"bending pipe tool\" proves useful in East African projects https://bbs.hcbbs.com/thread-5704226-1-1.html (Source: Haichuan Chemical Industry Forum)