IEC Cable Installation Methods: A1, A2, B1, B2, C, D, E and F

The installation reference method is not a label added after cable selection. It is part of the thermal model used to obtain the cable's reference current-carrying capacity. A cable surrounded by thermal insulation, enclosed in conduit, clipped to a surface, placed on a tray or buried in the ground rejects heat differently, so the same conductor size can have a different permissible current.

1. Why the installation method changes ampacity

The method determines which reference current-carrying-capacity data are appropriate. The overall model is:

If the method is wrong, the calculation starts from the wrong thermal reference point. Applying perfect temperature and grouping factors to the wrong Iz,ref does not repair that error.

2. Practical reference-method map

The following is a conceptual guide, not a reproduction of IEC tables. The exact method must be verified against the adopted edition and the detailed installation geometry.

• A1: insulated conductors or single-core cables in conduit within a thermally insulated wall.
• A2: multi-core cable in conduit within a thermally insulated wall.
• B1: insulated conductors/single-core cable in conduit on or near a wall.
• B2: multi-core cable in conduit or comparable enclosed surface installation.
• C: cable fixed directly on a surface / clipped direct, where heat dissipation is less restricted than enclosed methods.
• D1/D2: buried installation families; ducted and direct-buried arrangements require ground-temperature, soil and geometry assumptions.
• E: multi-core cable in free air / tray arrangements that meet the relevant reference geometry.
• F: single-core cables in free air under the relevant formation/spacing conditions.

IEC 60364-5-52 groups many detailed wiring arrangements into reference methods with similar current-carrying characteristics. The detailed standard contains more installation numbers and geometry conditions than the short list above.

3. Worked example: same load, different thermal reference

Consider a 32 A three-phase design current. Suppose the project's verified source data for one candidate conductor gives the following illustrative reference ratings:

• enclosed/insulated-wall arrangement: Iz,ref = 34 A;
• better ventilated surface arrangement: Iz,ref = 46 A.

Assume the same temperature factor 0.94 and grouping factor 0.80 for this demonstration:

The numbers above are intentionally illustrative rather than standards-table values. The engineering point is that method selection changes Iz,ref before correction factors are applied. A cable that is adequate on a ventilated tray may not be adequate when routed through a thermally restrictive section.

4. How to classify the real installation

1. Identify whether the cable is single-core, multi-core or insulated conductors in conduit.
2. Identify the thermal environment: insulation, wall/surface, tray/free air, duct or direct burial.
3. Check spacing, touching, formation and number of loaded conductors.
4. For buried circuits, establish ground temperature, soil thermal resistivity, burial depth and duct/direct-burial arrangement.
5. Use the detailed installation description in the adopted standard to select the reference method.
6. If the route changes materially, assess the thermally worst section rather than assigning one optimistic method to the whole run.

Select an IEC reference method in Cable Sizing

5. Assumptions and limits

• The reference letters are shorthand for detailed installation conditions; they do not replace the standard's geometry.
• Tray/free-air methods depend on spacing and formation, especially for single-core AC circuits.
• Buried ratings are highly sensitive to soil assumptions and may require IEC 60287 methods for non-standard conditions.
• Mixed routes can be governed by the most thermally restrictive section.
• Manufacturer current ratings may use a different declared basis; do not mix those ratings with unrelated correction factors.

Adjacent checks

After selecting the method, apply real service conditions using the cable derating guide. Then verify the result in the IEC Cable Sizing Calculator and check voltage drop with the Voltage Drop Calculator.

Engineering references

IEC 60364-5-52:2009+AMD1:2024 covers selection and erection of wiring systems. A practical public explanation of reference methods is available in the Electrical Installation Guide — General method for cable sizing.