Surface temperature failures are among the most avoidable reasons an ICT product fails certification, yet they remain a consistent finding in pre-compliance audits because engineers rarely treat heat as a design parameter from the schematic stage.
IEC 62368-1 governs audio, video, information technology, and communications equipment, and Clause 9’s Table 38 sets touch temperature limits for every accessible part, differentiated by material class and anticipated contact duration.
Understanding these limits at clause level means the test lab visit becomes a confirmation rather than a surprise.
This article explains how Table 38 is structured, what the TS1 limit values are for metal, glass, ceramic, plastic, rubber, and wood surfaces, and where GB 4943.1-2022 aligns with or diverges from the IEC source standard.
What Does IEC 62368-1 Table 38 Actually Specify?
IEC 62368-1 replaced IEC 60950-1 and IEC 60065 with a unified hazard-based framework. Rather than prescribing construction methods, it classifies hazards by energy class and defines the limits that safeguards must keep a body part below.
Thermal energy is one of those hazard domains, covered in Clause 9. Table 38 provides the touch temperature thresholds for accessible parts under normal operating conditions, with rows by material category and columns by contact duration.
The standard defines three thermal source classes. TS1 sources are unlikely to cause pain in ordinary persons, including children. TS2 may cause pain but not injury. TS3 can cause injury and requires safeguards before an ordinary person can access the surface.
Table 38 is the TS1 boundary. A part whose steady-state temperature exceeds the TS1 limit for its material category is classified as TS2 or TS3, and a safeguard is required between it and any ordinary person.
The temperature thresholds in Table 38 are based on IEC Guide 117, which in turn draws on the burn-threshold data in ISO 13732-1, the ergonomics standard for human responses to contact with hot surfaces. ISO 13732-1 provides the physiological data (for contact periods of 0.5 s and longer) but does not itself set surface-temperature limit values.
Sustained contact versus brief contact
Table 38 divides limits into two broad scenarios, and the distinction is more consequential than it first appears.
Sustained contact covers surfaces that a user touches during intended operation: a handle, a keypad, a volume dial, or any surface grasped or pressed repeatedly during use. This scenario carries the strictest limits.
Brief or inadvertent contact covers surfaces that are accessible but not normally touched, where a user who makes contact will withdraw reflexively before a burn can develop. Higher limits apply here.
The manufacturer determines which scenario governs each accessible part, and that determination must be documented. It is a testable claim, not a free administrative choice.
How Does IEC 62368-1 Classify Accessible Parts by Material?
IEC 62368-1 Table 38 uses material categories because the rate of heat transfer from a surface into skin depends on the material’s thermal effusivity, not on surface temperature alone.
At an identical surface temperature, metal deposits energy into the epidermis far faster than plastic does. The Table 38 limits reflect this: lower-effusivity materials are assigned higher allowable temperatures for the same contact duration.
Metal
Metal covers all uncoated metallic surfaces and metallic surfaces with coatings that provide no meaningful thermal barrier. A thin decorative paint layer does not reclassify the surface; the surface is assessed as metal.
Because metal has the highest thermal effusivity of the Table 38 categories, it carries the most restrictive limits at shorter contact durations. For sustained contact exceeding one minute, its TS1 limit equals the plastic and rubber limit at 48°C.
Glass, porcelain, and vitreous enamel
This category covers fired glass surfaces, ceramic, and enamelled metallic surfaces where the enamel provides genuine thermal separation. A cosmetic glaze over a metal substrate does not qualify without evidence of meaningful thermal insulation.
Glass and ceramic sit between metal and plastic in thermal effusivity. Table 38 includes them as a distinct material category with their own limit values, which sit between the metal and plastic extremes for most contact durations.
The specific TS1 values for glass and porcelain must be verified directly against IEC 62368-1:2018 before any compliance decision.
Plastic, rubber, and wood
This category covers enclosure panels, buttons, feet, gaskets, grip zones, and wooden structural elements. These materials have the lowest thermal effusivity of the three Table 38 categories.
Because plastic and rubber release stored energy to skin slowly, this category carries the highest allowable limits. A plastic surface at 77°C for a contact of one to ten seconds remains within TS1 territory.
WhWhy does the same surface temperature burn differently on metal and plastic?
The limits differ by material because the rate at which heat crosses into skin depends on thermal effusivity, not on surface temperature alone.
At an identical temperature, metal deposits energy into the epidermis far faster than plastic does. So the standard assigns metal the stricter limit and plastic the more permissive one for the same short contact.
A thin decorative coating does not change the classification. Paint over metal is assessed as metal; a glaze over a metal substrate is assessed as metal unless it provides evidence of genuine thermal separation.
Enamelled or fired surfaces qualify for the glass and ceramic category only where the layer delivers real thermal insulation, not merely a cosmetic finish.
How do TS1, TS2, and TS3 relate to each other?
The three classes form a graded scale, and the offsets between them matter more than any single number. TS1 is the boundary below which no thermal safeguard is required for ordinary persons.
TS2 sits 10 K above the TS1 value for the same material and duration. A TS2 surface reachable by an ordinary person needs either an equipment safeguard or an instructional safeguard between the surface and the user.
TS3 covers everything above TS2. For a surface an ordinary person can reach, TS3 requires a basic safeguard plus a supplementary safeguard, or a single reinforced safeguard.
Abnormal operating conditions shift the target. Where the equipment keeps running and the fault is not evident to an ordinary person, an accessible TS1 part must stay below the TS2 limit for its material and duration. If the malfunction is obvious to the user, no touch temperature limit applies, on the assumption the user will react. Identifying the component failure that drives the highest surface temperature is the starting point for single-fault thermal analysis.
Frequently Asked Questions
What is the IEC 62368-1 touch temperature limit for a continuously held metal surface?
For sustained contact exceeding one minute, the TS1 limit for metal is 48 °C, referenced to 25 °C ambient under normal operating conditions. Above that, the surface is TS2 and needs a safeguard against ordinary-person contact. Confirm the value against the current edition before a compliance decision.
Do metal and plastic have the same touch temperature limit under IEC 62368-1?
Only at the longest contact duration. For sustained grip beyond one minute, both converge on the same TS1 limit because the material no longer shields the skin over that timescale. At shorter durations the limits diverge, with plastic allowed the higher temperature — read the standard for the per-duration figures.
How does a manufacturer decide between sustained-contact and brief-contact limits?
The manufacturer designates each accessible surface by how the equipment is designed to be used, and documents it. It is a testable claim: if a test engineer concludes a surface is grasped in normal use, the sustained-contact limit applies regardless of the designation. Assess ambiguous surfaces against the stricter case.
Are the touch temperature limits in GB 4943.1-2022 different from IEC 62368-1?
No national deviation affecting touch temperature limits has been identified. GB 4943.1-2022 adopts the IEC 62368-1:2018 TS classification and limits, so a compliant product needs no extra thermal work on this point. The divergences lie in insulation coordination and overcurrent protection.
Which IEC 62368-1 edition sets the touch temperature limits I must meet?
EU harmonisation under the Low Voltage Directive has historically lagged the latest IEC edition, so the 2018 text still underpins most CE assessments, while IEC 62368-1:2023 is the newest edition. Confirm which edition your target market enforces, and whether the values or the contact-duration classification have been revised, before certification.ordinary persons requires either an equipment safeguard or an instructional safeguard between the surface and the person.
Conclusion
Material class and contact duration together set the applicable limit, and the manufacturer’s documented contact scenario is a testable claim a test engineer can challenge at any point. Material choice earns no margin on a continuously gripped surface but real headroom on a briefly touched one, which is where design effort pays off. Ambient headroom shrinks as rated operating temperature rises, so pre-compliance measurement belongs at maximum rated ambient, not at the bench.
As IEC 62368-1 moves through its edition cycle, confirming the current per-material limit values and the contact-duration classification directly against the standard should be a fixed step in every new product programme.
