Heat Traced Tubing in Hazardous Areas: ATEX, IECEx and T-Class

Analyser sample lines and instrument tubing often run through areas where flammable gas, vapour or dust can be present. An electrically traced tubing bundle placed there must not become a source of ignition. This guide explains which part of a bundle is certified, the standards and schemes involved, how zones, gas groups and temperature classes work, and what to send so the right heating cable is selected.

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Which part of a traced bundle is certified?

In an electrically traced tubing bundle, the heating cable is the electrical equipment. The tube, insulation and outer jacket are passive and carry no electrical rating of their own. Hazardous-area certification therefore applies to the heating cable and to the components that connect and terminate it, such as power connection, splice and end-seal kits.

In Techwin electrical heat traced bundles, the heating cables carry IECEx, ATEX and IEC certification. That certification is issued to the cable manufacturer, not to Techwin. When you review a bundle offer, ask which heating cable is used and check its certificate. IECEx certificates can be looked up in the public online register at iecex.com.

Steam traced and pre-insulated bundles contain no electrical parts. In a hazardous area, what matters for them is surface temperature: the hottest surface must stay below the ignition temperature of the gas present.

Standards and certification schemes

These are the documents and schemes buyers most often name in hazardous-area specifications for trace heating.

Name	What it is	Where it applies
IECEx	International certification scheme for equipment used in explosive atmospheres. Certificates are listed in a public online register.	Accepted in many countries, including much of the Middle East and Asia-Pacific
ATEX (Directive 2014/34/EU)	European Union law for equipment used in potentially explosive atmospheres. Certified equipment carries the CE mark and the Ex mark.	European Union and countries that adopt it
IEC/IEEE 60079-30-1	Electrical resistance trace heating in explosive atmospheres: general and testing requirements for the heating cable and its components.	Basis for IECEx and ATEX trace-heating certificates
IEC/IEEE 60079-30-2	Application guide for the design, installation and maintenance of trace heating in explosive atmospheres.	Design and installation practice
IEEE 515	Testing, design, installation and maintenance of electrical resistance trace heating for industrial applications.	Mainly North America

National schemes also exist, for example EAC Ex in the Eurasian Economic Union. Ask the buyer’s specification which scheme and which edition of each standard it requires.

Zones and gas groups

Under the IEC zone system, an area is classified by how often an explosive atmosphere is present. Trace heating is normally specified for Zone 1 and Zone 2 (gas) or Zone 21 and Zone 22 (dust); check the cable certificate for the zones it covers.

Zone	Explosive atmosphere is present	Medium
Zone 0	Continuously or for long periods	Gas or vapour
Zone 1	Likely in normal operation	Gas or vapour
Zone 2	Not likely in normal operation, and only for a short time	Gas or vapour
Zone 20 / 21 / 22	The same three levels for combustible dust	Dust

Gas groups describe how easily a gas ignites: IIA (for example propane), IIB (for example ethylene) and IIC (hydrogen and acetylene, the most easily ignited). Equipment certified for IIC also covers IIB and IIA. North America also uses the Class / Division system; a specification may give both.

Temperature classes (T-class)

The temperature class sets the highest surface temperature the equipment may reach. It must be below the auto-ignition temperature of the gas or vapour that may be present.

T-class	Maximum surface temperature
T1	450 °C (842 °F)
T2	300 °C (572 °F)
T3	200 °C (392 °F)
T4	135 °C (275 °F)
T5	100 °C (212 °F)
T6	85 °C (185 °F)

A lower temperature class number means a hotter allowed surface. T6 is the most restrictive. A gas with a low ignition temperature needs a higher T number.

How trace heating meets a temperature class

Self-regulating cable: output falls as the cable warms, so for many duties its sheath temperature stays within the T-class on its certificate without a separate limiter.
Constant-wattage and power-limiting cable: these do not limit their own temperature in the same way. Depending on the design and the certificate, the circuit may need a temperature controller or a separate temperature limiter.
IEC/IEEE 60079-30-1 recognises both approaches: a stabilised design, where the sheath temperature is shown to stay below the limit, and a controlled design, where a temperature limiting device keeps it there.
Steam-out or high process temperatures count too: the cable’s maximum exposure temperature must cover the hottest condition the line will see.

What to send for a hazardous-area bundle quotation

Area classification along the route: zone, gas group and the T-class required
Certification scheme required by the project: IECEx, ATEX or another national scheme
Maintain temperature, and the highest process or steam-out temperature the line can reach
Supply voltage and the length of each circuit
Lowest ambient temperature and site conditions (outdoor, UV, marine, chemicals)
Tube material, size and number of tubes, and how the bundle ends at the analyser or transmitter

Frequently asked questions

Is a heat traced tubing bundle ATEX or IECEx certified?

The certification belongs to the heating cable and its connection components, because they are the electrical equipment in the bundle. The tube, insulation and jacket are passive. In Techwin bundles the heating cables carry IECEx, ATEX and IEC certification, issued to the cable manufacturer.

What does T-class mean for trace heating?

The temperature class (T1 to T6) is the highest surface temperature the heating cable may reach. It must stay below the auto-ignition temperature of the gas present. For example, T3 allows up to 200 °C (392 °F) and T4 up to 135 °C (275 °F).

Can self-regulating heating cable be used in Zone 1?

Self-regulating cables are commonly certified for Zone 1 and Zone 2. Always check the zones, gas group and temperature class on the certificate of the specific cable proposed.

What is the difference between IECEx and ATEX?

IECEx is an international certification scheme with a public online register. ATEX is European Union law (Directive 2014/34/EU). Both test trace heating to the IEC/IEEE 60079-30-1 standard; projects state which one they require.

Bundles for classified areas

Send the area classification, temperatures, voltage and run lengths. We will reply quickly with a bundle proposal and the heating cable it uses.