§423 — Protection against burns: maximum accessible surface temperatures (Table 42.1)

The guide on lighting installations (§559) covers the fire risk a hot luminaire poses to nearby combustible material — including via the light beam itself. This article covers a related but distinct topic within the same "thermal effects" part of the standard (IEC 60364-4-42, chapter 42): §423 limits how hot an accessible part of fixed equipment is allowed to get during normal operation, so that a person cannot be burned simply by touching it — entirely independent of whether anything combustible happens to be nearby.

Why this is a separate requirement from fire risk

§422 (fire risk, see the guide on locations of increased fire risk, BE2) and §559 are concerned with a hot surface igniting something else. §423 addresses a different mechanism entirely: a surface that is not hot enough to be any kind of fire risk can still be hot enough to burn the skin of a person who touches it — a thermostat housing, a distribution-board enclosure, a motor casing, or a heater's outer surface can all fall into this category even where no combustible material is anywhere near it.

Table 42.1: three categories, metal versus non-metal

§423 sets the maximum surface temperature of an accessible part according to how the part is normally touched, and separately for metallic and non-metallic surfaces (a metal surface conducts heat away from the skin faster on contact, so it is felt as more severe at the same temperature and gets the stricter limit):

Type of accessible part	Metallic surface	Non-metallic surface
Hand-held for the purpose of operating the equipment (e.g. a handle, knob)	55 °C	65 °C
Intended to be touched but not hand-held (e.g. a housing surface likely to be brushed against)	70 °C	80 °C
Not intended to be touched during normal operation	80 °C	90 °C

The underlying logic: the closer and more deliberate the contact a part is designed for, the lower its permitted temperature — a part meant to be gripped and held is judged far more strictly than a part that is, at most, briefly brushed against.

Independent of the §524/§523 sizing checks

A surface-temperature problem under §423 is not caught by any of the usual cable- or protective-device-sizing checks: a correctly sized cable and a correctly rated protective device (see the guide on current-carrying capacity) say nothing about how hot the equipment enclosure itself gets in normal, fault-free operation — §423 is an entirely separate assessment, usually addressed through the design and product standard of the equipment itself rather than through the installation's electrical calculations.

Practical relevance

For most standard, CE-marked equipment, compliance with §423 is already built into the product's own design and its relevant product standard (for example a specific IEC standard for luminaires, heaters, or accessories), so it is rarely something an installer calculates from scratch. It becomes directly relevant when: siting equipment so that an accessible surface exceeding these limits cannot be reached in normal use (behind a guard, at height, or with a warning marking), assessing custom or panel-built equipment that does not fall under a specific product standard, or investigating a complaint about a surface that "feels too hot" — checking it against the correct limit for how that surface is actually touched, not against a single, universal number.

Common mistakes

Assuming a surface that merely "feels warm" is automatically acceptable, without checking it against the specific limit for the type of contact (hand-held, touched, or not normally touched) and the material.
Confusing §423 (burn protection for a person touching normally-operating equipment) with §422 (fire risk from a hot surface igniting nearby material) — both concern heat, but the underlying mechanism and the relevant limit are different.
Applying the loosest limit (80/90 °C) to a part that is actually hand-held, such as an operating handle or knob — the hand-held category carries by far the strictest limit (55/65 °C).
Overlooking that a product-specific standard (for a luminaire, a heater, or an accessory) can set its own, sometimes stricter, temperature limit that takes precedence for that specific product category over the general Table 42.1 values.