On one side, it opened the need for installing surge protection devices (SPD) in a very broad spectrum of applications – from public, commercial or industrial activities, even to consumer unit applications – as stated in section 443. On the second side, the 18th Edition (based on the EN 62305-4 and EN 61643-12) described the selection and the application of SPDs in section 534. The origin of the installation, the main switchboard, is the place to start the design of surge protection on the network.SPD selection criteria in the main switchboardsThe SPD protection design does not depend on the fault ratings given by the transformer, it only depends on the level of exposure in front of a surge. So, which SPD do we have to install in the main switchboard?In accordance with the IEC 61643 standard, there are three types of SPDs: Type 1, Type 2, and Type 3. Type 1 SPDs are the ones able to withstand the energy from a direct lightning strike. They have the ability to discharge high currents to earth. These kinds of SPDs are usually installed in the main switchboards (origin of the installation) for those cases where the level of exposure in front of a surge is very high, e.g. in a building that contains external lightning rod protection, high-exposed locations, or insulated installations. As it’s sometimes not possible to know the circumstances of the building at the design stage, there is a general practice for considering Type 1+2 SPDs in the main switchboard...
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