Nominal voltage (U_n)

The nominal value of the voltage of the current or signal circuit based on the use envisaged for the SPDs. The nominal voltage stated for an SPD corresponds to the system voltage of the typical SPD installation site for a standard three phase system, e.g.230/400 V AC. Systems with lower system voltages can also be protected by the SPD. In the event of higher system voltages, it must be decided on a casetocase basis as to whether the SPD can be used and if there are restrictions to observe.

Nominal load current (I_L)

Maximum r.m.s. value of the nominal current, which allows a connected load to flow to one of the protected outputs of the SPD. This maximum value is specified by the parts carrying operational current within the SPDs; these must be able to withstand the continuous thermal current load.

Short-circuit withstand capability (I_SCCR)

Maximum prospective short-circuit current of the electrical network, for which the SPD is rated in conjunction with the upstream over current protective device.The short-circuit withstand capability indicates the maximum prospective short-circuit current at which the SPD can be used at the installation location. The corresponding tests to determine this value are carried out in connection with the maximum permissible upstream.

Surge protective device(SPD)

Device that is intended to limit transient over voltages and divert surge currents. It contains at least one non-linear component [definition 3.1 of IEC 61643-1]

Maximum continuous voltage (Uc)

Maximum r.m.s. value of the voltage that is allowed to be continuously applied to the terminals of the SPD. The maximum continuous voltage must be at least 10% higher than the value of the nominal voltage. In systems with greater voltage deviations, SPDs with a greater difference between Uc and Un must be used.

Voltage protection level (Up)

Maximum voltage that can occur on the connection terminal blocks of the SPD while loaded with a pulse of specific voltage steepness and a discharge surge current of specified amplitude and wave form. This value characterizes the surge voltage protective effect of the SPD. In the event of a surge voltage or surge current within the performance parameters of the SPD, the voltage is safely limited to a maximum of this value at the protected connections of the SPD.

Lightning surge current (I_imp)

Peak value of the current flowing through the SPD with pulse shape (10/350μs). The pulse shape (10/350 μs) of a surge current is used for simulating the current flow of direct lightning strikes. The value of the lightning surge current is used for special testing of an SPD to demonstrate its load capacity with regard to high-energy lightning currents.Depending on the lightning protection class assigned to a lightning protection system, the SPDs must have minimum values that correspond to this peak value.

Nominal discharge current (I_n)

Peak value of the current flowing through the SPD with pulse shape (8/20μs). The pulse shape (8/20μs) of a surge current is characteristic of the effects of an indirect lightning strike or switching operation. The value of the nominal discharge current is used for a variety of tests on an SPD, including those used to determine the voltage protection level.Depending on the lightning protection class assigned to a lightning protection system, the SPDs must have minimum values that correspond to this peak value.

Off-load voltage (Uoc)

Off-load voltage of the hybrid generator at the terminal points of the SPD.A hybrid generator creates a combined surge; e.g., in offload. It supplies a voltage pulse with a defined pulse shape, generally (1.2/50 μs), and in a short circuit, a current pulse with a defined pulse shape, generally (8/20μs).The combined surge is characteristic of the effects of an induced surge voltage. Depending on the protection class assigned to a lightning protection system, the SPDs must have minimum values that correspond to this value.