Johannesburg, 25 Sep 2007
External lightning protection alone cannot provide complete safety, it only protects against fire and other damage to the building, and it is also unable to prevent power from a nearby lightning strike entering the building via the electrical supply.
This may damage electronic devices or even cause fires. Other typical causes for damaging electronic devices and information technology systems are switching operations in the power supply network.
Remember that the danger concerns not only households but also companies, which are dependent on fully functioning technical systems. Powerful information networks are the backbone of our modern industrial society. Failures of such systems may cause severe damage and loss, or may even lead to a company's bankruptcy.
The causes of disturbances related to IT systems are diverse. Reports from electronic insurance companies show alarming statistics that more than 30% of the damage has been caused by electromagnetic interferences.
To ensure continuous use of electrical or IT systems, even in the case of a direct lightning strike, further measures for surge protection have to be considered.
For this purpose, the Lightning Protection Zones Concept of IEC 62305-4 is applied. It simply means that a building is sub-divided into different risk zones where the necessary devices can be identified for lightning and surge protection. Depending on the requirements, lightning current arresters, surge arresters and combined lightning current and surge arresters would be utilised.
DEHN's Red/Line products offer comprehensive protection to the power supply provided external lightning protection is installed.
Lightning current arresters (Class 1) are installed inside the distribution board. They protect low-voltage installations against surge voltage and also in the case of direct lightning strikes.
Class 1 lightning current arresters must be used in conjunction with surge arresters (Class 2), which are installed in the sub-distribution board. They provide protection against surge voltages due to distant lightning strikes or peak voltages arising in the electrical power system.
Previously, a decoupling element had to be installed for subsequent installation of lightning current arresters and surge arresters with cable lengths under 15m. This is no longer required with the new Red/Line range of surge arresters.
Surge protection devices (Class 3) are installed at the terminal equipment absorbing the residual energy and provide protection against surges due to internal switching operations.
The failure of telephone, fax, computer or even complex computer controlled systems and machines, is a risk too high to accept. More than 25% of the damage in IT systems is caused by surge voltages, due to electromagnetic interferences.
When choosing the surge protection device, take a voltage protection level UP which is below the surge immunity level of the terminal equipment installed downstream in the communication/signalling circuit. Since this level is often unknown, it is necessary to use other means of comparison instead.
According to tests for electromagnetic compatibility (EMC), electrical and electronic equipment must have a certain immunity level against line-conducted disturbances (surges). The test set-up and the requirements for testing are stipulated in EN 61000-4-5 (VDE 0847 Part 5).
Installation classifications from 0 to X stand for certain electromagnetic environmental conditions. Depending on these installation classifications, different immunity levels (1-4) of the equipment are determined regarding the immunity against surges.
Equipment tested according to the test level 1 has the lowest surge immunity and equipment tested according to level 4 has the highest surge immunity. The test level is normally indicated in the specification of the equipment or can be obtained from the manufacturer.
With regard to the protection provided by the surge protective device this means that the let-through energy must be below the immunity level of the equipment to be protected.
The co-ordination characteristics describe the let-through energy of the surge protection device and the required surge immunity level of downstream equipment or the let-through energy of another downstream surge protective device.
Regarding the figures below, the first mark (here XX) gives information about the let-through energy of the surge protective device, the second mark (here X) about the required surge immunity level of downstream equipment or the let-through energy of another downstream surge protective device.
For a trouble-free operation, the indicated test level of terminal equipment eg,
3 must be higher than or similar to the test level demanded by the co-ordination characteristics of the protective device (e.g. 1, 2 or 3).