Electric Heat Tracing Cable Structure
1. Copper core conductor: 7×0.50, 19×0.32, 19×0.412. Conductive plastic layer: ordinary PTC, flame-retardant PTC, fluorinated PTC
3. Insulation layer: modified polyolefin, flame-retardant polyolefin, fluorinated polyolefin, perfluorinated material
4. Shielding layer: tinned soft round copper wire, coverage density 80%
5. Sheath layer: modified polyolefin, flame-retardant polyolefin, fluorinated polyolefin, perfluorinated material
3. Installation temperature: minimum: -5℃
4. Thermal stability: after 300 cycles between 15℃ and 99℃, the cable heat output remains above 90%.
5. Bending radius: 25.4mm at 20℃ room temperature, 35.0mm at -30℃ low temperature
6. Insulation resistance: for a cable length of 100m, at an ambient temperature of 75℃, using a 2,500VDC megohmmeter for 1 minute, the minimum insulation resistance (between conductor and shield) is 120MΩ.
7. Starting current (10℃): 0.4A per meter
8. Please refer to the precautions for installation and use
9. Maximum use length: not exceeding 100 meters
Structure Classification
Classification by Temperature
Depending on the composition of the polymer PTC material, self-regulating heating cables are divided into low-temperature and high-temperature types.
Common types on the market include heating cables with a temperature rating of 65℃ based on polyolefin, and heating cables with temperature ratings of 110℃ and 150℃ based on fluorinated materials. The temperature rating here is defined as the maximum ambient temperature (MAXIMUM PIPE MAINTENANCE TEMPERATURE) at which the heating cable can be effectively applied. It can also be understood as the highest ambient temperature at which the cable can be used stably for a long time and produce effective heating power output. Exceeding the specified temperature rating, on one hand, due to increased resistance, the cable's output power is very low, resulting in low actual heating efficiency. On the other hand, long-term over-temperature use can degrade or attenuate cable performance, such as PTC characteristics and heating power, reducing the cable's service life and operational reliability. However, short-term intermittent exposure to temperatures exceeding the rating is acceptable. Therefore, in addition to the above temperature ratings, self-regulating heating cables have another temperature rating. For example, for a cable with a 65℃ rating, the other rating is 85℃; for a 110℃ cable, it is 130℃; and for a 150℃ cable, it is 230℃. However, at this point, the effective output power of the cable is close to zero.
Due to the scarcity of relevant literature, many people have a misunderstanding about the temperature rating of self-regulating heating cables, thinking it refers to the maximum surface temperature of the heating cable. Thus, there are claims of 45, 65, 85, and 105℃ temperature ratings for polyolefin heating cables. In reality, because the cable's output power is related to ambient temperature, and the cable's surface temperature is closely related to the test ambient temperature and insulation conditions, it is unscientific and inaccurate to define the temperature rating of self-regulating heating cables by surface temperature. We need to remember that for polyolefin-based heating cables, the maximum continuous use temperature should not exceed 65℃.
Classification by Output Power
The output power of a self-regulating heating cable refers to the output power per unit length of cable at an ambient temperature of 10 degrees Celsius. Classified by heating power output, self-regulating heating cables come in three types: low, medium, and high. Generally, heating cables with a power less than 35 W/m are low-power; those with power greater than 35 W/m but less than 70 W/m are medium-power; and those with power greater than 65 W/m are high-power.
Classification by Application Area
General-purpose heating cable: a heating cable composed of copper conductors, polymer PTC material, and a single-layer flame-retardant sheath. Mainly used for heating or heat tracing of pipelines in general occasions. Explosion-proof reinforced heating cable: a metal mesh is added to the outer layer of the general-purpose cable. This structure can effectively eliminate static electricity and resist external mechanical impact. Mainly used in places with explosion-proof requirements.
Anti-corrosion and explosion-proof reinforced cable: this structure adds a fluorinated material layer on the outer metal mesh of the explosion-proof reinforced heating cable. This structure can effectively prevent and resist static electricity, mechanical impact, and various corrosive media. Mainly used in harsh environments or places with flammable and explosive materials.
Classification by Cable Use
Ordinary heating cable: a two-core heating cable. It consists of two parallel metal conductors covered with polymer PTC material and flame-retardant sheath material, or metal mesh and fluorinated material sheath. Due to the influence of conductor diameter and voltage drop along the length, the continuous use length of this cable generally does not exceed 200 meters.
Extra-long heating cable: a special five-core or six-core heating cable. In addition to the two parallel conductors covered with polymer PTC material, there are 3-5 insulated metal conductors arranged in the same direction, plus metal armor. Used for power transmission. This special structure allows the maximum continuous use length of the cable to not exceed 1100 meters, making it suitable for heat tracing of oil and gas pipelines and downhole heat tracing in oil fields.
Safety heating cable: a three-core heating cable. In the cable, a monitoring wire is arranged along the length inside the flame-retardant sheath. The monitoring wire can transmit information such as abnormal changes in output power, overcurrent conditions, and local damage along the line to the central control room in real time, facilitating timely understanding of the heating situation along the line and ensuring safe and reliable operation of the cable.
Classification by Applicable Voltage
Low-voltage type: heating cables with an applicable voltage range of 12-36V. These cables generally have low heating power and a continuous use length not exceeding 10 meters. Strict compliance with voltage requirements is necessary during use; otherwise, accidents such as cable fire may occur. Mainly used in civilian health products and heated seats for vehicles and ships.
Medium-voltage type: heating cables with an applicable voltage range of 100-660V. Generally, the self-regulating heating cables we refer to are of this type. In practical applications, 120V and 250V cables are interchangeable, but the maximum continuous use length of a 120V heating cable is usually half that of a 240V cable. The continuous use length of this type of cable generally does not exceed 200 meters.
High-voltage type: heating cables with an applicable voltage range of 380-650V. These are mainly the 5-6 core heating cables mentioned earlier. The continuous use length is generally greater than 500 meters.
Fire Causes
Fire at the End of Electric Heat Tracing Cable
Electric heat tracing cable installation includes laying the heat tracing on the outer wall of the equipment, the wiring box at the head and tail ends, the power distribution system, and the outer insulation layer. Today, the editor of electric heat tracing will briefly analyze which key points of electric heat tracing cable installation can cause end fires.
The end of the heat tracing cable needs to be sealed with a dedicated terminal junction box or heat shrink tubing. Due to the structure of the heat tracing cable, the two parallel bus bars already form an internal circuit. Therefore, during installation, connecting the two wires at the head end directly to the power supply neutral and live wires forms a complete circuit. The main causes of fire at the end of the electric heat tracing cable are as follows:
1. The tail end is a sealed section. During installation, a tail end junction box needs to be installed for sealing. It is strictly forbidden to leave the tail end of the heat tracing cable exposed without installing a junction box. If the tail end gets damp, it can easily cause a short circuit and fire.
2. When installing the tail end junction box, the outer sheath should be stripped off, and the shielding layer should be removed. It is strictly forbidden to connect the shielding layer of the heat tracing cable into the tail end junction box. If the shielding mesh is connected to the junction box, it can cause a ground fault. If the grounding protection is not in good contact, it can easily produce electric sparks and cause a fire.
3. The insulation layer at the tail end expands and contracts with temperature, exposing the conductive part. In rainy and snowy weather with high humidity, it can cause leakage and fire.
4. Using absorbent insulating tape can cause the tail end to become damp, leading to leakage and fire.
