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.
What Are the TS1 Touch Temperature Limits in IEC 62368-1 Table 38?
The values below are confirmed from IEC 62368-1 source documentation for metal and for plastic and rubber. The touch-temperature table was Table 42 in the 1st edition (2010) and became Table 38 from the 2nd edition (2014) onward; the current 3rd edition is IEC 62368-1:2018. Verify these values against IEC 62368-1:2018 before any compliance decision.
All Table 38 measurements run at 25°C ambient. When a product operates at higher ambient temperatures, the limits themselves do not increase; available thermal headroom for internal dissipation shrinks accordingly.
The TS1 touch temperature limits for metal and for plastic and rubber are as follows:
| Contact duration | Example contact scenario | Metal TS1 | Plastic and rubber TS1 |
|---|---|---|---|
| More than 1 minute | Continuous grip on a handle; falling against a surface without recovery | 48°C | 48°C |
| 10 s to 1 minute | Prolonged switch activation; adjusting a volume control | 51°C | 60°C |
| 1 s to 10 s | Pressing a button; intentionally activating a switch | 60°C | 77°C |
| Less than 1 second | Inadvertent touch with quick withdrawal | 70°C | 94°C |
A finding that regularly surprises design teams: at the longest contact duration, metal and plastic share the same TS1 limit of 48°C. The material differentiation becomes significant only at contact durations below one minute, and the gap widens substantially as duration shortens.
TS2 limits are given in the standard’s TS2 column; for the rows confirmed here they sit 10 K above the corresponding TS1 value. A metal surface touched inadvertently (less than one second) may reach 80°C before crossing from TS2 into TS3 territory. TS3 covers all temperatures above TS2 and, for a surface reachable by an ordinary person, requires a basic safeguard plus a supplementary safeguard (or a single reinforced safeguard).
How ambient temperature affects available margin
Table 38 limits are stated as absolute surface temperatures at 25°C ambient. The limit value does not change when a product’s rated operating ambient exceeds 25°C.
A product with a metal surface at 45°C during testing at 25°C ambient carries 3 K of margin against the sustained-contact limit. At 40°C ambient, that same surface will run warmer; pre-compliance testing should always be conducted at the product’s maximum rated ambient to expose this margin erosion before the formal test.
For thermocouple placement and stabilisation technique in surface temperature measurement, the IEC 60335-1 thermocouple placement guide and thermocouple types and placement articles cover the practical methodology that applies across product safety standards.
Table 38 under abnormal operating conditions
Under abnormal operating conditions where equipment continues to function and the malfunction is not evident to an ordinary person, accessible TS1 parts must not exceed the TS2 limit for the relevant material and contact duration.
For a metal surface under such conditions, the brief-contact TS2 limit is 80°C (70°C plus 10 K). If the malfunction is evident to an ordinary person, no touch temperature limit applies, on the assumption that the user will take appropriate action.
Identifying which component failure produces the highest surface temperature is the practical starting point for single-fault thermal analysis. The companion article Thermal Design for Compliance covers the pre-compliance methodology for controlling surface temperatures before formal testing, including the single-fault evaluation approach.
How Does GB 4943.1-2022 Compare to IEC 62368-1 on Touch Temperature?
GB 4943.1-2022 is the mandatory Chinese national standard for audio, video, IT, and communications equipment safety. It replaced GB 4943.1-2011 (based on IEC 60950-1) and absorbed GB 8898-2011 (the audio/video standard, equivalent to IEC 60065); mirroring the IEC 60950-1 + IEC 60065 merger into IEC 62368-1. It was issued in July 2022 and took effect on 1 August 2023.
The 2022 version adopts the IEC 62368-1:2018 hazard-based framework, requiring recertification for products previously certified under the legacy standard. The transition imposed significant changes for manufacturers supplying the Chinese market, both in documentation approach and in engineering scope.
Where GB 4943.1-2022 aligns with IEC 62368-1
GB 4943.1-2022 adopts the TS1, TS2, and TS3 classification structure, and the touch temperature limits for accessible parts track IEC 62368-1 Table 38 without specific national deviations on this topic.
A product meeting IEC 62368-1 Table 38 TS1 limits does not require additional thermal engineering to meet the equivalent GB 4943.1-2022 requirement. Test conditions and measurement approach are the same.
Where GB 4943.1-2022 diverges from IEC 62368-1
The national deviations in GB 4943.1-2022 address China’s specific power distribution and infrastructure conditions. Three areas drive the most significant design differences for products targeting both markets.
The deviations address the following: overcurrent protection, requiring products to incorporate protection independent of building wiring; ground isolation, requiring isolation measures between protective and signal grounds; and insulation, where stricter air clearance requirements apply alongside additional performance requirements for high-humidity environments.
None of these deviations affect surface temperature requirements. A product meeting IEC 62368-1 Table 38 TS1 limits needs no additional thermal engineering work to meet GB 4943.1-2022 on this specific point.
Products designed for both EN 62368-1 and GB 4943.1-2022 should address insulation coordination and grounding architecture during early design, not as a retrofit. CCC (China Compulsory Certification) under GB 4943.1-2022 also requires engagement with a designated Chinese test laboratory, and the documentation submission process differs from EU conformity assessment. Planning for these requirements from the project outset reduces timeline risk considerably.
Frequently Asked Questions
What is the IEC 62368-1 touch temperature limit for a metal surface that is continuously held during normal use?
For sustained contact exceeding one minute, the TS1 limit for metal under IEC 62368-1 is 48°C, measured at 25°C ambient under normal operating conditions. A metal surface above 48°C in this scenario is classified as TS2 and requires a safeguard to protect ordinary persons from direct contact.
Do metal and plastic surfaces have the same touch temperature limit under IEC 62368-1 Table 38?
At the longest contact duration (more than one minute), yes: both metal and plastic share the TS1 limit of 48°C. The differentiation becomes significant at shorter durations. For a contact of one to ten seconds, the TS1 limit is 60°C for metal and 77°C for plastic — a 17 K spread driven entirely by the difference in thermal effusivity between the two material classes.
How does a manufacturer determine whether a surface is sustained contact or brief contact under IEC 62368-1?
The manufacturer designates each accessible surface based on how the equipment is designed to be used, and the designation must be documented. It is a testable claim: if a test engineer concludes that a surface can be grasped during normal operation, the sustained-contact limit applies regardless of the manufacturer’s designation. Ambiguous surfaces should be assessed against the stricter scenario.
Are the touch temperature limits in GB 4943.1-2022 different from those in IEC 62368-1?
No specific national deviations affecting touch temperature limits have been identified. GB 4943.1-2022 adopts the IEC 62368-1:2018 TS classification and Table 38 limits. A product meeting IEC 62368-1 Table 38 does not require additional thermal engineering to meet GB 4943.1-2022 on this point. The compliance gaps between the two standards lie in insulation coordination and overcurrent protection architecture.
What does the TS2 limit mean in IEC 62368-1, and when does it apply to accessible surfaces?
TS2 limits sit 10 K above the TS1 value for each contact duration and material row. They apply in two situations: to surfaces accessible to ordinary persons under abnormal operating conditions where the malfunction is not evident to the user, and to surfaces that instructed persons rather than ordinary persons are permitted to contact during normal use. A TS2 surface accessible to ordinary persons requires either an equipment safeguard or an instructional safeguard between the surface and the person.
Conclusion
Material class and contact duration together determine the applicable Table 38 limit, and the manufacturer’s documented contact scenario designation is a testable claim that a test engineer can challenge at any point in the certification process.
For sustained contact exceeding one minute, metal and plastic share the same TS1 limit of 48°C; the material differentiation that matters most in engineering practice occurs at contact durations below one minute, where the gap between metal and plastic limits reaches 17 K at the one-to-ten-second band.
GB 4943.1-2022 aligns with IEC 62368-1 on touch temperature limits, and the compliance gaps between the two standards sit in insulation coordination and overcurrent protection, not in Table 38 values.
As IEC 62368-1 continues through successive edition cycles, confirming whether Table 38 values or the contact duration classification approach have been revised should be a standard pre-certification step for any new product development programme.
