SPD Surge Protection Devices – Types & Uses

Surge Protection Devices (SPD’s) are designed to reduce the risks caused by power surges from lightning strikes, heavy load switching & overvoltages etc. There are three main types of Surge Protection Devices, Type 1, Type 2 and Type 3, there are also some combined SPD units such as 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 above 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

• Type 1 = Protection against flash-over from direct lightning strikes to building structure or to LV overhead supply.
• Type 2 = Protection against overvoltage’s which can stress the electrical installation.
• Type 3 = Protection against overvoltage’s and high currents on items of equipment.
• ​Type 1+2 would offer both the protection of a Type 1 and Type 2 SPD combined.

To determine which SPD type you require you would need to carry out a risk assessment to ascertain the level of risk associated with each type of electrical surge. Surge protection is required when there is a risk to life or livestock should a power surge occur.

To offer maximum surge protection you could install a Type 1 SPD at the origin of the installation, a Type 2 at each local consumer unit and Type 3 SPD local to the equipment it needs to protect.

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”

BS7671 References

• Appendix 16 – Devices for the Protection Against Overvoltages (page 507-512)
• Section 443 – Protection Against Transient Overvoltages or Atmospheric Origin or due to Switching (page 100)
• Section 534  – Devices for the Protection Against Overvoltage (page 160)
• 534.4.7 – SPD Installation in Conjunction with RCD’s (page 168)

Protection of Sensitive Electronic Equipment

To assist in the protection of electronic equipment a Type 3 SPD would be required to protect against over-voltage’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 Beama Guide to Surge Protection.
[btn_download link=”/wp-content/uploads/2020/06/Beama-Guide-to-Surge-Protection-Devices.pdf” ] Beama Guide to Surge Protection Devices (SPD’s)

Fore more information on the Electrical Tools and Reference App visit » Electrical Tools and Reference