Ambient, core & installation temperature

Around cables several temperature factors are involved.

During installation:

• Ambient temperature at installation.

After installation:

• ambient temperature during operation

• wire temperature during operation. 

Installation temperature or ambient temperature at installation

Ideally the ambient temperature should not be lower than 0 or 5°C. Cable materials become stiffer at low temperatures. Manipulating the cable at such temperatures can cause cracks, which will render the installation unreliable. The minimum temperature for installation can be found on the technical data sheet.

If you strictly observe rules of good craftsmanship, cable can be installed at low temperatures down to -20°C:

• The cable must be kept in a heated room of at least 20°C for 24 hours.
• During installation, the temperature of the cable sheathing must be carefully monitored. If it cools down too much (below 5°C), it must be warmed up again for 24 hours.
• The bending radius must be strictly respected during installation. Bending a cable too far puts a lot of tensile forces on it and since the materials are stiffer because of the cold, there is an increased risk of cracks.

Maximum conductor temperature in service

When current flows through a conductor, it heats up through the joule effect. The more current, the warmer the conductor becomes. If the temperature of the conductor rises too high, its insulation will begin to melt, which may lead to short circuits. The maximum conductor temperature is therefore limited by the insulation material around the core.

In other words: at equal section, you can send more current through a cable insulated with XLPE than one with PVC because the one with XLPE can handle a higher core temperature. This is the reason why the old PVC-insulated VMvK have been replaced by YMvK insulated with XLPE.

To preserve the lifespan of your cables, it is advisable not to continuously load the cables up to the maximum core temperature as this will accelerate the thermal ageing process.

Ambient temperature during use or operating temperature

The construction standards of the standard installation cables determine the permissible ambient temperature during operation with the range -15°C to 60°C.

Upper range limit

If the environment becomes too hot, it will heat up the cable in addition to the heating caused by the joule effect. This shortens the lifespan of the cable and increases the risk of short circuits.

This permissible maximum ambient temperature of 60°C also applies to fire-resistant cables. Fire resistant cables can withstand the high temperatures reached during a fire for a limited period of time (1 to 2 hours), but will then carbonise and need to be replaced.

If higher ambient temperatures are expected, suitable cable types must be selected.

Lower range limit

The permissible minimum ambient temperature is also important. Cable materials become stiffer under the influence of cold.

If the cable has to operate at colder temperatures, the rules of good craftsmanship must be followed carefully:

• The cable must not move at all after installation. This means that it must not be moved and absolutely not exposed to vibrations. This can cause cracks, as the cable materials are very stiff due to the cold.
• The cable fixings must of course also be able to withstand the expected freezing temperature - if they were to shrink under the influence of the cold, they could squeeze the cable sheathing to such an extent that the cable would be damaged in that area.