Cables and conductors must be protected by means of overcurrent protective devices against excessive warming, which may result both from operational overloading and from short-circuit.

Overload protection [t-head1-nnp]

Overload protection means providing protective devices which will interrupt overload currents in the conductors of a circuit before they can cause temperature rises which may damage the conductor insulation, the terminals and connections or the area around the conductors.

For the protection of conductors against overload the following conditions must be fulfilled (source: DIN VDE 0100-430)

I_B anticipated operating current of the circuit

I_Z current-carrying capacity of the cable or conductor

I_n rated current of protection device

Note:

For adjustable protective devices, In corresponds to the value set.

I₂ The current which causes tripping of the protective device under the conditions specified in the equipment regulations (high test current).

Arrangement of protection devices for overload protection [t-head3]

Protection devices for overload protection must be fitted at the start of every circuit and at every point where the current-carrying capacity is reduced unless an upstream protection device can ensure protection.

Note:

Reasons for the current-carrying capacity being reduced:

Reduction of the conductor cross-section, a different installation method, different conductor insulation, a different number of conductors.

Protective devices for overload protection must not be fitted if interruption of the circuit could prove hazardous. The circuits must be laid out in such a way that no possibility of overload currents occurring need be considered.

Examples: