When designing the installation, it is assumed that the current density in copper conductors in the loaded section may be 6 - 10A / mm? constantly, and in the sections loaded occasionally, but for a short time, it should not exceed 16A / mm?. The load depends on the quality of the insulation and cooling conditions, moreover - e.g. in pipes where several pairs of wires are flying together - there should be a lower load, while in an overhead installation, where the wires are hanging apart from each other and are well cooled, higher densities can be assumed.
The copper resistance is 0.0175 Ohm * mm? / m, so a cable with a cross-section of 1.5mm? and a length of 10m (2x5m) has a resistance of 0.116 ohms, i.e. the current flow of 8.7A to the 2kW / 230V boiler will generate 8.8W of power in it, which in such a section should not heat the cable by more than 1 degree Celsius above the ambient temperature, the start power is 8.8 / 2000 = 0.44% of the supplied power.
Do you already know how it is designed?
