Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
IEC 62086 Electrical Resistance Trace Heating in Explosive Gas Atmospheres
General Requirements and Application Guide for Explosion-Protected Heat Tracing Systems
IEC 62086 (now consolidated into IEC 60079-30) specifies the general requirements and application guidelines for electrical resistance trace heating systems used in explosive gas atmospheres. It is the cornerstone standard for heat tracing design in the oil, gas, and petrochemical industries where flammable atmospheres may be present during normal or abnormal operation.
1. Explosion Protection Design Requirements for Trace Heating
IEC 62086-1 establishes the general requirements and test methods for electric resistance trace heating systems in hazardous areas. The standard mandates that the maximum surface temperature of the heating cable must remain below the auto-ignition temperature (AIT) of the surrounding gas atmosphere under both normal and fault conditions. Electrical connection components must carry appropriate Ex d (flameproof) or Ex e (increased safety) protection ratings, and the system must incorporate reliable ground-fault protection to detect any insulation degradation before it leads to arcing or sparking.
The standard classifies trace heating cables into two fundamental types: constant-power (series-resistance) and self-regulating (parallel-resistance with PTC characteristics). Self-regulating cables offer inherent safety advantages in hazardous environments because their power output decreases automatically as temperature rises, eliminating the risk of localised overheating even when cables are crossed or overlapped. Constant-power cables deliver uniform watt density over long distances, making them preferable for applications requiring precise temperature control over extended pipeline sections — but they require strict adherence to the prohibition on cable crossing.
| Parameter | Self-Regulating (PTC) | Constant Power |
|---|---|---|
| Power output characteristic | Decreases with temperature | Constant along length |
| Maximum maintenance temperature | Typically ≤ 150 °C | Up to 260 °C |
| Cross-over / overlap safety | Permitted | Prohibited |
| Suitable hazardous zones | Zone 1, Zone 2 | Zone 1, Zone 2 |
| Maximum circuit length | Shorter (inrush current limited) | Longer (hundreds of metres) |
| Temperature classification | T3 — T6 typical | T1 — T6 selectable |
In Zone 1 areas, prioritise self-regulating cables for their intrinsic PTC safety characteristic. If constant-power cables are unavoidable, each circuit must be equipped with independent over-temperature thermostats and validated by thermal analysis confirming that overlap cannot occur under any installation or maintenance condition.
2. Temperature Classification and Hazardous Area Matching
The temperature classification (T-rating) system defined in IEC 60079-0 forms the basis for matching trace heating systems to hazardous areas. The T-rating (T1 through T6) specifies the maximum allowable surface temperature of electrical apparatus in relation to the auto-ignition temperature of the gases or vapours present. IEC 62086 requires that the heating cable’s maximum surface temperature — under both normal operation and defined fault conditions — must never exceed the T-rating limit of the classified area.
Practical trace heating design requires engineers to evaluate several interdependent factors: the process maintenance temperature, minimum ambient temperature including extreme winter conditions, thermal insulation type and thickness, wind-induced convective heat loss, and supply voltage tolerance (± 10 % typical). The standard provides detailed heat-loss calculation formulas and safety correction factors for various pipe sizes, insulation materials, and environmental conditions. A safety margin of at least 10 °C between the cable’s maximum surface temperature and the T-rating limit is recommended to account for measurement uncertainty and aging effects.
| T-Rating | Max Surface Temperature | Typical Gases |
|---|---|---|
| T1 | ≤ 450 °C | Hydrogen, methane, ammonia |
| T2 | ≤ 300 °C | Ethylene, ethane, propane |
| T3 | ≤ 200 °C | Gasoline, diesel, hydrogen sulphide |
| T4 | ≤ 135 °C | Diethyl ether, acetaldehyde |
| T5 | ≤ 100 °C | Carbon disulphide |
| T6 | ≤ 85 °C | Ethyl nitrate |
A common design pitfall is selecting the T-rating based only on normal operating conditions without considering fault scenarios such as thermostat failure or thermal insulation damage. A self-regulating cable with damaged thermal insulation may operate at higher power output, potentially exceeding its nominal T-rating. The standard recommends including insulation-loss fault simulation in type testing.
3. Installation, Commissioning, and Maintenance per IEC 62086-2
IEC 62086-2 provides comprehensive practical guidance for the design, installation, commissioning, and maintenance of trace heating systems. The standard emphasises that installation must be carried out by certified personnel with hazardous-area competence, and that every installed circuit must undergo insulation resistance testing, ground continuity verification, and functional performance validation before being put into service. The handover documentation package must include as-built drawings, heat-loss calculations, thermostat calibration records, and Ex certification documentation for all components.
Key installation aspects include: cable routing methodology (straight tracing for small-diameter pipes, spiral wrapping for valves and flanges, sinusoidal patterns for large-diameter vessels), Ex-rated junction box specifications with proper cable gland entries, thermostat and sensor placement for representative temperature sensing (typically at the coldest pipe section), weatherproof sealing of thermal insulation at all termination points, and permanent labelling with circuit identification and Ex marking. For maintenance, the standard recommends periodic inspection routines: visual examination of heating cable outer jacket integrity, ground-fault protection device testing, calibration verification of temperature controllers against actual pipe surface temperature, and thermal insulation condition assessment.
Mechanical damage during maintenance — particularly when removing and reinstalling thermal insulation — is the most common failure mode in industrial trace heating systems. Always coordinate cross-disciplinary work schedules and install visible warning markers along the heating cable path before any insulation removal work begins. A robust “permit-to-work” system with explicit trace-heating isolation procedures is essential for safe maintenance operations.
Frequently Asked Questions
Q1: What is the relationship between IEC 62086 and IEC 60079-30?
IEC 62086 has been consolidated into the IEC 60079-30 series (Part 1: General and testing requirements, Part 2: Application guide). The 62086 designation is still widely referenced in legacy documentation, but for new installations, IEC 60079-30 should be consulted as the current governing standard.
Q2: How is a self-regulating heating cable certified for explosive atmospheres?
Self-regulating cables must undergo IECEx or ATEX certification covering: surface temperature measurement under normal and fault conditions, mechanical impact resistance, dielectric strength, insulation resistance, and accelerated aging. The certificate specifies the Ex marking (typically Ex e mb or Ex e) and the applicable T-rating.
Q3: What commissioning tests are essential for trace heating systems?
Essential tests include: cold insulation resistance (≥ 20 MΩ), hot insulation resistance (≥ 5 MΩ at operating temperature), ground loop resistance (≤ 1 Ω), RCD/GFCI trip test at 30 mA, and power output measurement per circuit verifying deviation from design within ± 10 %.
Q4: How is pipe heat loss calculated for trace heating design?
The standard references ISO 12241 calculation methods. The fundamental formula is Q = U × A × ΔT, where U is the overall heat transfer coefficient (determined by insulation thermal conductivity, thickness, and ambient conditions), A is the pipe surface area, and ΔT is the difference between maintenance temperature and minimum ambient temperature. A safety factor of 1.1 to 1.3 is typically applied.
