Reference methods — determining the installation method for the current-carrying-capacity table

The guide on cable cross-section & current-carrying capacity covers the base formula Iz = Itabel × f1 × f2 × f3. That article assumes the correct Itabel value is already known. This article covers the step that precedes it: how the physical way a cable is or will be installed is translated into one of the reference methods from IEC 60364-5-52 — the key used to look up the correct table.

Why the installation method determines the table value

The same cable with the same cross-section has a different current- carrying capacity depending on how well the generated heat can be dissipated: a cable free in air cools better than the same cable embedded in a thermally insulated wall, and a cable in a cable tray alongside several other cables cools differently than a single cable on an open cable tray. IEC 60364-5-52 captures this by grouping installation methods into a limited set of reference methods, each with its own column in the current-carrying-capacity tables.

The main reference methods

Method	Typical installation
A1	Insulated conductors or single-core cable in conduit, in a thermally insulated wall
A2	Multi-core cable in conduit, in a thermally insulated wall
B1	Insulated conductors or single-core cable in conduit, on a wooden or masonry wall
B2	Multi-core cable in conduit, on a wooden or masonry wall
C	Single-core or multi-core cable clipped directly to a wall or ceiling (or embedded in a wall), without conduit
D	Cable buried directly underground, or in an underground conduit
E	Multi-core cable free in air, or on a cable tray/ladder
F	Single-core cables free in air, touching each other

As you go further down this table, heat dissipation generally improves and the permitted current-carrying capacity (at equal cross-section) tends to be higher — a cable free in air (method E/F) is usually allowed to carry noticeably more current than the same cable embedded in an insulated wall (method A1/A2).

From installation method to reference method

In practice, the reference method is not read off directly, but determined via a separate, more extensive example table (annex to IEC 60364-5-52) that links concrete installation situations — for example "cable in a tray on a perforated ladder" or "cable embedded in concrete" — to the corresponding reference method from the list above. This step is essential: choosing the wrong reference method directly leads to the wrong Itabel value, regardless of how carefully the correction factors f1/f2/f3 are applied afterwards.

Practical relevance

When sizing or checking a cable cross-section, identifying the correct reference method is the first step, before looking up Itabel and applying the correction factors: a cable calculated during design as method E (free air) but later actually embedded in an insulated wall (method A1/A2) has an assumed current-carrying capacity that is too high without recalculation.

Common mistakes

Keeping the same reference method regardless of changes in the installation method — a cable that ends up embedded in an insulated wall or enclosed cable tray during execution requires a fresh look-up of the reference method.
Assuming method E or F (free air) for an easier calculation while the cable is actually embedded in a wall or conduit — this results in an overly optimistic (too high) Itabel value.
Applying the reference method of a single cable to a bundle without also applying the separate grouping correction factor (f2) from the cable cross-section guide — the reference method and the grouping correction are two separate steps that are both required.
Ignoring the example table and estimating the reference method yourself based on a superficial resemblance — the official example table contains installation situations that are not always intuitively linked to the correct letter method.