Electric Heating Cable Type Cable Structure
According to the different composition of polymer PTC materials, self-regulating heating cables are divided into low-temperature and high-temperature types.
Commonly available on the market are heating cables with polyolefin as the base material at a 65°C temperature rating and those with fluoropolymer as the base material at 110°C and 150°C temperature ratings. 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 operate 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 small, resulting in low actual heating efficiency. On the other hand, long-term use at overtemperature 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 65°C rated cable, this temperature is 85°C; for a 110°C rated cable, it is 130°C; and for a 150°C cable, it is 230°C. 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, believing it refers to the maximum surface temperature of the heating cable. Hence, there are claims of 45, 65, 85, and 105°C temperature ratings for polyolefin heating cables. In reality, because the output power of the cable is related to the ambient temperature, and the surface temperature of the cable is closely related to the ambient temperature during testing and the insulation condition, it is unscientific and inaccurate to define the temperature rating of self-regulating heating cables by surface temperature. We need to remember that for heating cables based on polyolefin, the maximum continuous operating temperature should not exceed 65°C.
Classification by Output Power
The output power of a self-regulating heating cable refers to the output power per unit length of the cable at an ambient temperature of 10°C. According to the heating power output classification, self-regulating heating cables are divided into three types: high, medium, and low. Generally, heating cables with a power less than 35 W/m are low-power heating cables; those with a power greater than 35 W/m but less than 70 W/m are medium-power heating cables; and those with a power greater than 65 W/m are high-power heating cables.
Classification by Application
General-purpose heating cables: These are heating cables composed of copper conductors, polymer PTC material, and a single layer of flame-retardant jacket. They are mainly used for heating or heat tracing of pipelines in general applications. Explosion-proof enhanced heating cables: These cables have an additional metal mesh layer over the general-purpose cable, which can effectively eliminate static electricity and resist external mechanical impact. They are mainly used in places with explosion-proof requirements.
Anti-corrosion explosion-proof enhanced cables: These cables have an additional fluoropolymer layer over the metal mesh of the explosion-proof enhanced heating cable. This structure effectively prevents and resists static electricity, mechanical impact, and various corrosive media. They are mainly used in harsh environments or places with flammable and explosive materials.
Classification by Cable Usage
Standard heating cable: This is a two-core heating cable. It consists of two parallel metal wires covered with polymer PTC material and a flame-retardant jacket material, or a metal mesh and fluoropolymer jacket. Due to the influence of conductor diameter and voltage drop along the length, the connected length of this cable generally does not exceed 200 meters.
Extra-long heating cable: This is a special five-core or six-core heating cable. In addition to the two parallel wires covered with polymer PTC material, there are 3-5 additional insulated metal wires placed in the same direction, plus an outer metal armor for power transmission. This special structure allows the maximum continuous 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: This is a three-core heating cable. In the cable, a monitoring wire is placed along the length inside the flame-retardant jacket. The monitoring wire can transmit information such as abnormal output power changes, overcurrent conditions, and local damage along the line to the central control room in real time, facilitating timely understanding of the heating conditions along the line and ensuring safe and reliable operation of the cable.
Classification by Applicable Voltage
Low-voltage type: These are heating cables with an applicable voltage range of 12-36V. Such cables generally have low heating power and a continuous length not exceeding 10 meters. Strict compliance with voltage requirements is necessary during use; otherwise, accidents such as cable fire may occur. They are mainly used in civil health products and heating seats for vehicles and ships.
Medium-voltage type: These are heating cables with an applicable voltage range of 100-660V. The self-regulating heating cables we generally refer to are of this type. In practical applications, 120V and 250V cables are interchangeable, but the maximum continuous length of a 120V heating cable is typically half that of a 240V cable. The continuous application length of such cables usually does not exceed 200 meters.
High-voltage type: These are heating cables with an applicable voltage range of 380-650V. They are mainly the 5-6 core heating cables mentioned earlier. The continuous application length is usually greater than 500 meters.
