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The installation process defects of heating cables directly affect system safety, heating effect, and service life. The core focus is on five aspects: laying, fixing, connecting, protecting, and supporting construction. The specific types, manifestations, and hazards of defects are as follows, which are convenient for on-site investigation and rectification:

1、 Defects in laying process: directly causing uneven heating and insulation damage

Cable spacing deviation too large/too small

• Defect manifestations: failure to lay according to the design spacing, local dense stacking, and uneven spacing between edge areas;
• Harm: Too small spacing can cause local overheating, accelerate insulation aging, and too large spacing can lead to insufficient temperature, with an overall temperature difference exceeding 3 ℃;
• Typical scenario: Difficulty in laying in the corners of ground heating walls and around pipelines, with cables being randomly wrapped; The spacing was not controlled during the spiral winding of pipeline insulation.

The bending radius does not meet the standard and is excessively bent

• Defect manifestation: Cable bending radius less than the manufacturer's requirements, right angle bending, repeated bending;
• Harm: Cracking of metal sheath, breakage of magnesium oxide insulation layer, or damage of polymer insulation layer (self limiting heating cable), causing a decrease in insulation resistance and leakage;
• Common causes: using tools to forcefully break cables during construction, and forcibly bending cables when crossing narrow spaces.

Overlapping and cross laying of cables

• Defect manifestation: Multiple cables crossing, single cable overlapping on its own;
• Harm: The heat at the overlapping area cannot be dissipated, and the local temperature exceeds the upper limit of the cable's temperature resistance, causing the insulation layer to melt, short circuit, and even fire;
• Mistake prone point: intentionally overlapping and winding cables to increase heating power during pipeline insulation.

The cable is not tightly attached to the controlled object

• Defect manifestation: During ground heating, the cable is suspended in the gap of the insulation layer, and during pipeline insulation, the cable is not tightly attached to the surface of the pipeline;
• Harm: Decreased heat transfer efficiency, slow heating rate, and low temperature in the suspended area;
• Common causes: uneven surface of the controlled object and failure to compact the cable during fixation.

2、 Fixed process defects: causing cable displacement and stress damage

Improper fixing method can damage the cable

• Defect manifestation: Fixed with iron wire and plastic cable ties (iron wire scratches the sheath, plastic cable ties melt at high temperature), sharp fixing fixtures;
• Hazard: Cable sheath damage, exposed insulation layer, causing electrical leakage; After the plastic cable tie melts, the cable shifts and the spacing is disrupted;
• Correct requirement: Fix with stainless steel clamps and ceramic insulators, and the fixture should be round and free of edges and corners.

The fixed point spacing is too large, causing the cable to sag

• Defect manifestation: Horizontal laying fixed point spacing>50cm, vertical laying>30cm, or no fixed point set in corners or turns;
• Harm: Due to self weight sagging and displacement, the originally uniform spacing of the cable is damaged, and local stretching causes the sheath to crack;
• Typical scenario: When laying vertically on the walls of a tall space, the fixing points are not encrypted as required, and the cables sag in the middle section.

Excessive fixing force, squeezing the cable

• Defect manifestation: excessive force when tightening the clamp, squeezing the cable sheath (such as deformation of MI cable metal sheath, depression of insulation layer of self limiting cable);
• Harm: The magnesium oxide insulation layer inside the MI cable is broken, and the heating core of the self limiting cable is compressed, resulting in local power abnormalities (overheating or no heating);
• Judgment method: After fixing, the cable sheath should have no obvious deformation, and the cable should be gently pulled by hand without displacement.

3、 Connection process defects: the weakest link in the system, which can easily cause leakage and short circuits

Improper joint production

• Defect manifestation:Failure to seal the cables in a timely manner after cutting them on site, and failure to fill the joints with sealant;
• Harm: Decreased insulation resistance, leakage, and even short circuit burning at the joint;
• Correct requirement: Priority should be given to using prefabricated joints from the manufacturer, and on-site joints should be welded firmly and sealed in multiple layers.

The wiring terminals are loosely connected or crimped

• Defect manifestation: The wire is directly twisted with the temperature controller/power terminal, and the terminal screws are not tightened;
• Harm: Excessive contact resistance at the virtual connection point can cause heating and burn out the terminals, and even lead to a fire; Unstable current transmission and insufficient heating power of cables;
• Mistake prone: Multiple wires are inserted into the terminal without being tightly twisted, or the copper nose does not match the cross-sectional area of the wire.

Violation, interference or damage in the laying of the circuit

• Defect manifestation:The cable did not pass through the protective tube when passing through the wall/equipment;
• Harm: Electromagnetic interference can cause the thermostat to malfunction, cables to start and stop frequently, and wires to break, leading to short circuits;
• Correct requirement: Separate the installation of strong and weak electricity, and use metal protective pipes at the crossing points.

4、 Defects in protective technology: insufficient ability to resist the environment, accelerated aging

Insufficient moisture-proof and waterproof measures

• Defect manifestation:The joints in outdoor/humid environments (such as basements and pipeline wells) are not equipped with waterproof junction boxes, and the junction boxes are not sealed;
• Harm: Moisture seeps into the insulation layer of the insulated heating cable, causing a decrease in insulation resistance and corrosion of the sheath;
• Typical scenario: When insulating outdoor pipelines, the joints are exposed to rain and snow without rain covers.

 Lack of protection against high temperature/corrosive environments

• Defect manifestation:Corrosion resistant sheathed cables have not been used in corrosive environments, nor have they undergone anti-corrosion treatment;
• Harm: Overheating, aging, corrosion and damage of cable sheath, shortening the service life by 30%~50%;

Grounding process defects

• Defect manifestation: The metal sheath of the cable, junction box, and temperature controller housing are not grounded, or the grounding resistance is greater than 4 Ω;
• Harm: When the protective sheath is damaged, electric leakage occurs, making it unable to enter the ground and causing electric shock accidents;
• Correct requirement: Use a yellow green grounding wire of ≥ 2.5mm ² and multiple grounding points.

5、 Common process defect investigation methods

• Appearance inspection: The cable is free of scratches, deformations, overlaps, firmly fixed, and the joint seal is intact;
• Insulation resistance test: Use a 500V megohmmeter to measure the insulation resistance of the cable to ground, and it is qualified if it is ≥ 50M Ω (dry state);
• Power on test: After 1 hour of power on, scan with an infrared thermal imaging device, and there should be no local overheating (>80% of cable temperature resistance) or low temperature areas (temperature difference from normal areas>3 ℃);
• Joint inspection: There is no heating at the joint (measured with a thermometer, which should be close to the ambient temperature) and no leakage.

The installation process defects of heating cables mainly include "non-standard connection, improper fixation, uneven laying, and lack of protection", among which joint production and insulation protection are the most prone to safety accidents. It is recommended to provide specialized training for personnel before construction, strictly follow the manufacturer's instructions and specifications for operation, and have professional personnel complete key processes. After installation, defects should be checked item by item to avoid operation with defects.