Specify the hazardous-area temperature requirement, but do not assume every cable gland or blanking plug needs its own T5 or T6 marking. Acceptance depends on the enclosure protection concept, component certification, permitted temperature range and installed conditions. A passive entry component may have a certified service-temperature range rather than an independent temperature class. The purchase specification must establish suitability for the complete assembly, not merely request matching letters on separate parts.
Temperature class and service temperature mean different things
A temperature class limits the maximum surface temperature of equipment under the conditions covered by its certification. For the gas and vapour temperature-class system, T5 and T6 mean the following:
| Temperature class | Maximum surface temperature | What it does not establish |
|---|---|---|
| T5 | 100 °C | The permitted ambient range or cable-entry temperature |
| T6 | 85 °C | The temperature capability of every seal, cable or accessory |
T6 imposes a lower surface-temperature limit than T5. It does not automatically establish suitability for a particular atmosphere or protection concept. Gas group, equipment protection level and other certification requirements still apply.
A service-temperature range describes the temperatures within which a component can perform its certified function. For a gland, that includes the ability of its seals and construction to maintain the required protection.
These are different limits. A gland permitted to operate at 100 °C does not thereby make an assembly suitable for T6. Conversely, a T6 enclosure marking does not establish that every entry remains below a particular seal's maximum temperature.
Combustible-dust applications require a separate assessment of maximum surface temperature, dust characteristics and possible deposits. Do not select dust equipment from gas temperature classes alone. The combustible-dust enclosure selection article explains that broader selection problem.
Start with the enclosure protection concept
Identify the enclosure's complete hazardous-area marking and certification before selecting its entries. The area classification alone does not define the gland construction.
For a flameproof enclosure using Ex d protection, the entry arrangement must preserve the certified flameproof boundary. Cable construction, gland design and any sealing arrangement must meet the applicable certification and installation requirements.
For an increased-safety enclosure using Ex e protection, entries must maintain the required mechanical retention, sealing and protection concept. An Ex e marking does not eliminate temperature limits on seals or cable materials.
For intrinsically safe circuits using Ex i protection, energy limitation addresses ignition risk within the circuit. It does not automatically remove enclosure, environmental or cable-entry requirements. Whether a separately Ex-certified gland is necessary depends on the permitted installation arrangement and applicable documentation.
Neither “always use a T6 gland” nor “passive glands never need assessment” is a reliable purchasing rule.
Environmental sealing alone does not establish hazardous-area suitability. The distinction is covered in environmental protection versus hazardous-area junction box suitability. We do not build hazardous-location enclosures.
What certification establishes and what it leaves to the installation
A gland or plug certificate applies to a defined product, construction and set of conditions. Depending on the protection concept, its assessment may cover mechanical retention, sealing, impact resistance, temperature capability or flameproof performance.
Not every passive entry component generates heat that requires an independent temperature classification. Its documentation may instead specify a service-temperature range and conditions for incorporation into equipment. A missing standalone T-class marking is therefore not automatically a defect.
The opposite also applies. A T6 marking does not prove that an entry matches the enclosure threads, cable construction or certified installation arrangement.
Obtain and review:
- The certificate and its schedule for the exact gland or plug variant.
- Installation instructions, including permitted seals, washers and accessories.
- Any special conditions of use, commonly indicated by an X suffix in IEC-based certification schemes.
- Any component-certificate limitations, commonly indicated by a U suffix in those schemes.
- The enclosure certificate and instructions governing its entries.
A component certificate does not, by itself, approve a complete installation. Resolve incorporation requirements before purchase.
Also identify the jurisdiction and required approval scheme. IEC-based Ex markings and North American classification systems are not interchangeable purchasing descriptions. The Class 1 Division 2 selection requirements address that wider approval question.
Compare ambient temperature with actual entry temperature
Record the minimum and maximum site ambient temperatures. Then determine the temperature at the installed entry, including heat conducted from the enclosure and equipment inside.
Ambient temperature is not necessarily the temperature experienced by the gland seal. A bottom entry beside lightly loaded terminals may experience different conditions from an entry beside hot power equipment. Sunlight and nearby hot pipework can also change the local temperature.
Consider a hypothetical selection with these documented conditions:
- Maximum site ambient temperature: 40 °C.
- Assessed maximum temperature at the entry: 72 °C.
- Proposed gland's permitted service-temperature range: −20 °C to 80 °C.
The 72 °C entry temperature is within that stated range. This comparison alone does not establish the assembly's temperature class or hazardous-area approval. It also does not establish cable suitability unless the cable's own temperature limits are checked.
At the cold end, check both operation and installation restrictions. A cable or seal may tolerate a low operating temperature but require warmer conditions during installation.
Use the thermal assessment required by the enclosure documentation and applicable standards. Do not substitute one normal-operation temperature reading for assessment of all required operating and fault conditions.
Match the cable and entry threads
Temperature suitability cannot compensate for the wrong cable seal. Specify the actual cable construction, not just conductor count and nominal conductor size.
For an unarmoured cable, provide the outside diameter and its manufacturing tolerance. For an armoured cable, also provide the armour type, relevant diameters and armour dimensions required by the gland manufacturer. Include sheath material and any cable-construction details needed to assess sealing or gas migration.
For example, a cable measured at 0.47 in [12 mm] must fall within the selected seal's documented clamping range. That dimensional check is necessary, but hazardous-area suitability still depends on the certified cable and gland arrangement. The cable gland clamping-range article covers the basic dimensional check.
Do not assume that every flameproof entry requires the same barrier arrangement. Determine any barrier-gland requirement from the enclosure documentation, cable characteristics and applicable installation rules.
Specify the entry thread's system, nominal size, pitch or taper, and available engagement. Parallel and tapered threads do not seal or engage in the same way. The G-thread versus NPT adapter article explains the dimensional distinction; hazardous-area adapters need their own suitability review.
Never treat thread tape, extra sealant or an improvised washer as a substitute for the certified entry arrangement.
Apply the same review to blanking plugs
An unused opening remains part of the protection boundary. Its blanking plug must suit the enclosure protection concept, thread, temperature conditions and environmental exposure.
Do not substitute a transport cap, ordinary pipe plug or general-purpose closure merely because its threads appear to fit. Obtain the specified closure and follow its documented installation requirements.
A passive blanking plug may have a permitted temperature range without a separate T5 or T6 marking. As with a gland, acceptance depends on its documentation and incorporation into the enclosure.
Include adapters, reducers and sealing accessories in this review. Each additional interface introduces another compatibility question. Avoid stacking accessories unless the applicable documentation permits that arrangement.
What to put on the purchase specification
Use the following grouped checklist to request a documented selection. Ask for the exact proposed variants, not a general statement that the components are suitable for hazardous areas.
Area and enclosure requirements
- State the installation jurisdiction and required approval scheme.
- Provide the area classification, gas or dust group, and required protection level.
- State the enclosure protection concept and complete certification reference.
- Include the required equipment temperature class or dust surface-temperature limit.
- Attach the enclosure's entry restrictions and special conditions of use.
Temperature and environmental conditions
- State the minimum and maximum ambient temperatures.
- Provide the assessed entry-temperature range and its engineering basis.
- Identify cable temperature limits and any installation-temperature restrictions.
- Describe water, chemicals, ultraviolet exposure, vibration and corrosion conditions.
- Request confirmation that seals and accessories cover those conditions.
Cable and mechanical details
- Provide cable construction, sheath material and outside-diameter range.
- Include armour details and other sealing diameters where applicable.
- Specify thread form, size, pitch or taper, and available engagement.
- Identify wall thickness, sealing faces and required accessories.
- List every unused opening and its proposed blanking plug.
The cutout specification guide explains how to communicate opening geometry. For hazardous equipment, however, an accurate drawing does not authorize machining or modification. Obtain the enclosure manufacturer's documented acceptance before changing certified entries.
Required documents and acceptance
Request certificates, schedules, installation instructions and a written explanation of temperature suitability. Where no standalone T-class marking applies, ask which documented temperature limits govern the component's use.
Have the responsible hazardous-area designer verify the proposed entry schedule against the complete enclosure assembly. Accept the parts only when protection concept, temperatures, cable construction and mechanical interfaces all agree.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 30 × 24 × 10 in | 304 stainless | 30 x 24 x 10 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Does every hazardous-area cable gland need a T6 marking?
Not necessarily. A passive cable gland may be certified with a service-temperature range rather than an independent temperature class. Its acceptance depends on the enclosure protection concept, certificate conditions and actual installed temperatures. The complete equipment must still satisfy its required temperature class.
What is the difference between T5 or T6 and a gland's service-temperature range?
T5 limits maximum equipment surface temperature to 100 °C, while T6 limits it to 85 °C, under the conditions covered by certification. A gland's service-temperature range describes its permitted operating conditions. Neither value replaces checks of cable limits, seals, ambient temperature or entry temperature.
Do intrinsically safe circuits remove cable gland temperature requirements?
No. Intrinsic safety limits circuit energy, but it does not automatically remove mechanical retention, environmental sealing or enclosure requirements. Whether a separately Ex-certified gland is required depends on the installation arrangement, applicable standards and enclosure documentation. The actual temperature conditions still need assessment.
How should a hazardous-area blanking plug be specified?
Treat the plug as part of the enclosure protection boundary. Confirm its permitted protection concept, temperature range, thread compatibility and certification conditions. A transport cap or ordinary threaded plug is not an acceptable substitute merely because it fits the opening.
