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Performance Characteristics of Heat Tracing Cable

Performance Characteristics of Self-Regulating Heat Tracing Cable

Self-regulating heat tracing cable can automatically limit the working temperature of the cable during heating; it can automatically adjust the output power according to the temperature changes of the heated system without external equipment; the cable can be cut to any length or extended within a certain range without changing the above performance; it allows cross-overlapping and winding without risk of overheating or burning; the temperature of the traced pipeline is uniform, without overheating, safe and reliable; energy-saving; fast start-up for intermittent operation; low installation and operation costs; easy installation, use, and maintenance; convenient for automated management; no environmental pollution; long service life, etc.

Performance Characteristics of Constant Power Heat Tracing Cable

The heat output per unit length of constant power parallel electric heating cable is constant. The longer the cable used, the greater the total output power, and the higher the pipeline maintenance temperature. This electric heating cable can also be cut to any length on site as needed. In addition, due to its flexibility, the cable can be easily attached to the pipeline surface. The outer metal shielding mesh of the cable can prevent static electricity and provide safe grounding. It not only improves the overall strength of the cable but also plays a role in heat transfer and dissipation.

Basic Structure and Classification of Self-Regulating Cables

Temperature Classification

According to 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°C based on polyolefin, and 110°C and 150°C heating cables based on fluoropolymer 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 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 output power of the cable itself is very small, resulting in low actual heating efficiency. On the other hand, long-term overtemperature use will 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 also 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 of the temperature rating of self-regulating heating cables, thinking 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, since 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 state, 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 use temperature should not exceed 65°C.

Classification by Heating Output Power

The output power of self-regulating heating cables 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: low, medium, and high power. 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 Area

General-purpose heating cable: refers to a heating cable composed of copper conductors, polymer PTC material, and a single layer of flame-retardant sheath. Mainly used for heating or tracing of pipelines in general occasions. Explosion-proof reinforced heating cable: a layer of metal mesh is compounded on 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 type: this structure adds a layer of fluoropolymer material on the outer layer of the metal mesh of the explosion-proof reinforced heating cable. This structure can effectively prevent and resist static electricity, mechanical collision, 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 wires coated with polymer PTC material and flame-retardant sheath material or metal mesh and fluoropolymer sheath. Due to the influence of conductor diameter and voltage drop along the length, the continuous use length of this cable is generally not more than 200 meters.
Extra-long heating cable: a special structure of five-core or six-core heating cable. In addition to the two parallel wires coated with polymer PTC material, there are 3-4 additional insulated metal wires in the same direction, plus metal armor. Used for power transmission. This special structure allows the maximum continuous use length of the cable to exceed 1100 meters, so it can be used for tracing of oil and gas pipelines and downhole tracing in oil fields.
Safety heating cable: a three-core heating cable. In the cable, a monitoring wire is placed 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: refers to 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 adherence to 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: refers to 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 application length of this type of cable is usually not more than 200 meters.
High voltage type: refers to 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.

System Composition

Any model and specification heat tracing cable, such as self-limiting electric heating tape, constant power electric heating tape, etc.
Explosion-proof power junction box: used to protect the safe wiring of the electric heating tape. The quality of the connection is related to the safe use and service life of the electric heat tracing system. The common model is FDZ.
Explosion-proof intermediate junction box: facilitates the connection of electric heating tape on complex pipeline routes. Under the premise of not exceeding the maximum use length, it can also be used as a power junction box. Common models are FIH and FTH, etc.
End junction box: one end of the self-limiting electric heating tape is connected to the power supply, and the other end is sealed with an end junction box or heat shrink tubing. It is strictly forbidden to connect the two ends of the electric heating tape or connect the two parallel bus wires. FZH
Explosion-proof temperature controller: uses a thermocouple temperature control probe to sense the temperature of the heating tape, manual precise temperature control. PTC self-limiting electric heating tape may not be installed. For heating tapes that use heating wires to generate heat, such as constant power electric heat tracing, a temperature controller must be used to limit the temperature. Common model BJW.
Aluminum foil tape: used to expand the heating area of the electric heating tape, increase the range of heat collection and insulation, and improve tracing efficiency.
Heat-sensitive tape: used to fix the electric heat tracing system, generally sticking the electric heating tape to the traced pipeline or related equipment. Stainless steel tie straps can also be used for fixing.
Warning label: after construction, stick it on the outer surface of the traced pipeline as a sign and power-on warning.

Installation and Construction of Heat Tracing Cable

Installation and construction are key to using heat tracing cable effectively. Read carefully before installation and have it done by a professional electrician. The installation process is roughly divided into:
1. Confirm whether installation conditions are met; 2. Install heat tracing cable and terminations; 3. Install power junction box; 4. Measure insulation resistance; 5. Connect power and switch; 6. Power-on test; 7. Make electric heat tracing markings; 8. Repeat steps 4 and 6; 9. Apply insulation and waterproofing; 10. Acceptance.

Installation Conditions

Heat tracing cable installation should be carried out after the main project is completed, i.e., no welding, lifting, or other operations should be performed above the installation location to avoid damage. Confirm that the pipelines or equipment to be traced have been leak-tested and cleaned, and any burrs, sharp edges, or protrusions on the surface have been smoothed.

Installation Steps

Heat tracing cable should be distributed according to the pipeline length to prevent material from cooling and solidifying where there is no heat tracing cable. The length of the heat tracing cable should be longer than the traced pipeline. During installation, verify that the total length of the heat tracing cable used (including the total length of parallel branches) does not exceed the design length or the maximum allowable use length. When laying, try to make the heat tracing cable lie flat and close to the surface of the pipeline or container, and fix it with polyester tape or aluminum foil tape. Do not use thin wire for binding. The tape spacing should be less than 30mm. For flanges, valves, and other sharp protrusions, pay attention to protection. When installing on horizontal pipelines, it can be laid at 45 degrees below the pipeline. Multiple cross-overlapping is allowed during installation, but twisting should be minimized as much as possible. To enhance the tracing effect, a layer of aluminum foil tape can be applied on the outside of the heat tracing cable. When installing on a container, the heat tracing cable should be wound around the middle and lower part of the container, usually not exceeding 2/3. After installation, perform an insulation test on each heat tracing cable. The resistance between the heat tracing cable core and the pipeline or container should not be less than 20 MΩ. Otherwise, find the cause before connecting the power and applying insulation. This test should be performed multiple times. The test results should be recorded for future reference.

Electrical Connection

First, check that the cross-section of each branch power wire is slightly larger than the core cross-section of the heat tracing cable. The main power wire should be able to withstand the total current of all heat tracing cables at the lowest ambient temperature. Each heat tracing cable should have its own switch, fuse, or single-pole circuit breaker. When stripping the heat tracing cable core, avoid breaking strands to reduce cross-section and cause overload.
1. Connection between heat tracing cable and power junction box: In flammable and explosive places, a matching explosion-proof power junction box must be used. In general places, the heat tracing cable can be directly connected to the knife switch, or the wires can be twisted or welded and sealed with quick-drying silicone and heat shrink tubing. The twisted joint should not be shorter than 30mm, and the welded joint should not be shorter than 10mm.
2. Branching of heat tracing cable: In flammable and explosive places, a matching explosion-proof straight junction box must be used. In general places, twisting or welding can also be used.
3. Extension of heat tracing cable: In flammable and explosive places, a matching explosion-proof straight junction box must be used. In general places, twisting or welding can also be used. When extending, be careful not to exceed the maximum use length.
4. Termination: In flammable and explosive places, a matching termination sealing box must be used. In general places, quick-drying silicone and heat shrink tubing can also be used for sealing. Under any circumstances, it is strictly forbidden to connect the tail cores.
5. Power junction box: T-type, straight junction boxes, and terminations can be fastened to the pipeline with clamps or nylon ties. The waterproof rubber gasket inside the box must not be omitted. The wiring inside the box should be waterproofed with quick-drying silicone. When applying insulation, the junction box should be placed inside the insulation layer, but corresponding markings must be left on the insulation layer.

Applying Insulation and Waterproofing Layers

Applying insulation and waterproofing layers is an important part of the heat tracing cable system. It must be installed strictly according to the design requirements, especially outdoors. Once rainwater penetrates the layer, the insulation capacity will be greatly reduced. If the sheath is damaged, it may cause electrical breakdown, sparks, or hidden fire. Therefore, strengthen on-site management to prevent construction personnel from accidentally damaging the heat tracing cable. After the insulation test passes, the insulation and waterproofing layers should be installed as soon as possible. During installation, prevent metal sheets from cutting the heat tracing cable sheath. The screws for fixing the iron sheet should not be too long to avoid puncturing.

Installation of Heat Tracing Control Alarm Box

According to relevant specifications and combined with the actual situation of the project, the positioning principles for the electric heat tracing control alarm box were explored and formulated: ① Based on the location of the distribution room; ② Does not affect the installation of other electrical equipment; ③ The wall for installation is a solid wall; for ceramsite or hollow brick walls, add a bracket; ④ The height position is best for easy observation and easy maintenance. Based on the above positioning principles and the layout of the electric heat tracing system pipelines, a two-line heat tracing cable control alarm box was adopted. They are placed in the distribution rooms or duty rooms on both sides of the platform and the distribution room on the station hall floor. The distribution box in the distribution room supplies 220V voltage to the control box. Each heat tracing cable control box connects two dual-conductor heating cables to heat the fire-fighting water supply pipes under the platform slab and in the ceiling of the station hall floor. The heat tracing control alarm box must be installed strictly according to the design requirements.
The installation height and vertical error of the box should be controlled within the allowable range of the specification. The wiring inside the box should be neat and beautiful, with reasonable routing, bundled into bundles, and properly fixed. The connection between the wire and the electrical appliance must comply with the specification: stranded wires should be tinned after crimping, and single wires should be wound in a spiral direction. When using bolt top tightening, insert the double wire diameter, and the exposed conductor length at the insulation end should not exceed 3 mm. For conductors with a cross-section of 25 mm² or more, open-type terminals should not be used. The movable contact end of the control appliance must be the load end. Each distribution branch and control circuit should be clearly marked in a dedicated nameplate frame.