Safety requirements for cables and electrical lines

Basic requirements

Cables can be regarded to be safe in case that they are used for their intended purpose and don’t mean any unaccep-table risk for life and real values. If not otherwise specified, insulated cables shall only be used for the transmission and division of electric energy.

General requirements

Cables have to be chosen in a way that they meet the existing voltages and currents occuring in the machines, equipment of appliances or in their parts for which they are applied under any expected operating condition. Cables should be constructed, installed, protected and maintained to avoid any risks and harms.

Carrying capacity for undisturbed service (general info)

The cable section has to be chosen in a way that the given current-carrying capacity never leads to a heating of the conductor over the allowed service temperature. The heating resp. carrying-capacity of a cable depends on the construction, material characteristics and the operating conditions. Additional heating due to a cable accumulation, heating flues, solar radiation, etc. have to considered resp. avoided. The use of covers requires an undisturbed air circulation.

Operating conditions

The temporary flow of current describes the operating conditions. Con tinuous operation means a constant current which is at least sufficient to reach the thermal equilibrium of the electrical equipment without any other time limit. The capacity values of cables are based on continuous service reaching the allowed operating temperature of the conductor.

Environmental conditions

Environmental conditions are among others characterized by the ambient temperature, heat loss and heat radiation. The ambient temperature is the temperature of the surrounding air, without any load on the respective cable. The reference point is a temperature of +30 °C. The operating conditions of cables can change by heat loss for example in closed rooms, cable ducts or similar, as well as by heat radiation (e. g. solar radiation).

Conditions and requirements for fixed laying

The fixed laying of cables requires among others

The cable shall not be installed in direct or close contact with hot surfaces if they are not suitable for this application.
Cables are not suitable for direct underground laying.
Cables have to be fixed properly. The weight of the cable is important for the choice of the fixing distance.
The used mechanical fixing devices shall not damage the cable.
Cables that have been used for a long time may be damaged in case of removal. This can be a natural effect due to the ageing of the
physical characteristics of insulation and sheath material - they become brittle.

Requirements for flexible cables

Flexible cables should be used for mobile electrical equipment.
The length of the connection cable has to be chosen in a way that the reaction of short-circuit protective equipment is ensured.
For mobile electrical equipment the cable should be as short as possible.
Elevated stress due to tension, pressure, abraison, torsion or knicking has to be avoided.
The cables shall not be damaged by strain relief or connection devices.
The cables shall not be layed under carpets or other devices.
There is a risk due to elevated thermal covering and mechanical damage due to walking, furniture or operating material.
The cables shall not be in direct or close contact with hot surfaces.

For further requirements please see HD 516 S2 pos. 4.4.

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