The standard IEC 60364-5-52 in paragragh B.52.6.1 Reference methods specifies

Reference methods A1, item 1 of Table A.52.3 (insulated conductors in conduit in a thermally insulated wall) and A2, item 2 of Table A.52.3, (multi-core cable in conduit in a thermally insulated wall):The wall consists of an outer weatherproof skin, thermal insulation and an inner skin of wood or wood-like material having a thermal conductance of at least 10 W/m2·K.
The conduit is fixed so as to be close to, but not necessarily touching the inner skin.
Heat from the cables is assumed to escape through the inner skin only.
The conduit can be ****l or plastic.
Example of sizing cable

Electrical load named LOAD 2 is fed by Circuit 2 of switchboard DB2 3~400V as shown in Fig. 1 below
Load given data

  • Installed power P = 3.0 kW
  • Power factor p.f(cosφ) = 0.85
  • Number of Phases: 1
  • Line to neutral voltage U = 231 V
  • Load current Ib = 15.3A (calculated Ib=P/(U*cosφ))
  • Protective device rated current MCB In=16A (Sized from condition In > Ib)Cable given data

    • Cable type: Copper conductor, PVC insulation, PVC sheath, harmonized deignation H05VV
    • Installation Method: In plastic conduits inside the wall
    • Number of circuits in the conduit: 3
    • Room temperature: 35 °C
    • Length L=15 m
    • Permitted voltage drop ΔU = 2 %