... Type 1+2. The type of SPD you may require to protect your electrical installation will depend on the level of protection you are looking to achieve, such as protection against lightning strikes or just local protection to electronic equipment. The SPD chart below is a sample of the many electrical charts in the Electrical Tools & Reference App which shows the different types of surge protection devices and their applications.
Types of SPD's
SPD's and Lightning Protection Systems
If a building has a Lightning Protection System then generally a Type 1 SPD would be required to protect against flash-over from direct lightning strikes to the structure or to the LV overhead supply. In many cases the installation may also require a Type 2 SPD to protect against overvoltage's caused by a lightning strike therefore a Type 1+2 combined SPD maybe suitable.
SPD's and the 18th Edition Wiring Regulations
BS 7671 18th edition Appendix 16 (page 507-512) shows an informative for "devices for the protection against overvoltage" including the different earthing system types and SPD requirements. Section 443 details "protection against transient overvoltages or atmospheric origin or due to switching"
Protection of Sensitive Electronic Equipment
To assist in the protection of electronic equipment a Type 3 SPD would be required to protect against overvoltage's and high currents on items of equipment. The type 3 SPD would generally be installed locally to the equipment it is to protect against the effects of surges.
For more information on Surge Protection Devices (SPD) download the Bema Guide to Surge Protection.
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