Lightning and surge protection may only be installed, put into operation and maintained by qualified electricians who are familiar with national and international laws, regulations and standards. Among other things, normative requirements regarding line lengths, effective protection areas and fuse protection of surge protection devices must be observed.
Surge protection devices are always installed where cables are fed into the control cabinet. This prevents interference from being coupled into the control cabinet. They are diverted directly at the beginning of the control cabinet.
As a general rule, a surge protection device should be installed as close as possible to the power supply point of the electrical system. The insert of the appropriate SPD shall ensure voltage limitation in accordance with the insulation coordination. This protects the downstream installation equipment.
The insulation strength from the main distribution board up to and including the sub-distribution board is 4 kV. The surge arrester (type II) is normally installed in the sub-distribution board and then limits the voltage to below 4 kV.
The insulation strength from the sub-distribution board to the end device is 2.5 kV. The end device surge protection (type III) is ultimately located directly in front of the device to be protected and limits the voltage to below 2.5 kV.
All SPDs have an earth-connection terminal point. The earthing wire for the associated equipotential bonding rail must be connected to this point. The earthing wire must be as short as possible with the largest possible cross-section, since each centimetre of line length increases the residual voltage of the SPD.
In type I arresters, both earth-connection terminals must be connected. One cable leads to the equipotential bonding connection on the building and the second cable is connected to the PE conductor on the installation.
Due to the inductive conductor resistant, a transient voltage surge can quickly cause a voltage drop of multiple 1,000 V. This would degrade the effective protection level of a SPD so far that the voltage resistance of the installation or the device to be protected could be exceeded despite the use of an SPD. In the worst case scenario, the device could be damaged, destroyed or a fire could even be started.
The incoming and outgoing cables are connected directly to the terminals of the SPD. This results in a V-shaped connection geometry. This method minimises line lengths and reduces additional voltages and contact resistances.
A cable is branched off from the main circuit and connected directly to the surge protection device. This results in a T-shaped connection geometry. Wiring may cause higher interference because the line length is greater and additional contact resistance may occur.
To ensure effective protection, the surge protection must be installed as close as possible to the feed point for the electrical system. For a residential building, for example, this is directly at the mains infeed in the bottom connection area of the meter cabinet.
Potential intrinsic sources of interference within the building must also be taken into consideration. In these cases, the surge protection also needs to be installed as close as possible to the triggering device.
The standard (VDE 0100-534) regulates the maximum distance between a surge protection device and the devices to be protected (effective protection range).
As a rule, the same cable cross-section is selected for the connecting cables to the SPD as for the outer conductor (L1, L2, L3) and the neutral conductor (N).
The standards IEC 603640100-534 (VDE 0100-534) require the minimum cable cross-sections shown in the table for type I and type II SPDs.
| Type | Connecting lines between SPD and line conductor | Connecting lines between SPD and main grounding busbar or protective earth (PE or PEN) |
| I | 6 mm2 Cu (copper) | 16 mm2 Cu(copper) |
| II | 2.5 mm2 Cu(copper) | 6 mm2 Cu(copper) |
For safety reasons, SPDs are protected against short circuits or overloads by means of an overcurrent protection element (F2) designed for the type of installation and the cross-section of the connected cable.
The cable cross-sections and backup protection for surge protection devices with a short-circuit resistance (Isccr) of 50 kA and 25 kA are shown in the table as examples.
In normal operation, SPDs act as passive, non-conductive components. A flow of current occurs only in the case of a surge voltage or at the end of the service life for the protective components. For this purpose, the SPDs are protected against short circuits or overloads by means of an overcurrent protection element (F2).
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