In this article, Andrew Duffen, Technical Commercial Engineer at NAPIT, presents the ultimate guide to Surge Protective Devices.
As Surge Protective Devices (SPDs) find their way into installations more often, we need to be aware of the different ways they can be installed and the different types that are available.
Not all SPDs are the same. Some devices are specifically designed for use in TT installations and must be fitted in the correct part of that installation, with regards to any residual current devices (RCDs) that are installed.
What is an SPD?
An SPD is a protective device that is installed to safeguard electrical systems, including the consumer unit, wiring and associated components, from power surges, which are referred to as transient overvoltages.
It also provides protection for sensitive electronic devices connected to the system, such as computers, televisions, washing machines, as well as safety circuits like fire detection systems and emergency lighting. Electronics with delicate circuitry are particularly susceptible to damage caused by these transient overvoltages.
What are transient overvoltages?
Transient overvoltages are brief electrical surges that happen when energy, previously stored or introduced by other methods, is suddenly discharged. These overvoltages can arise from both natural events (lightning strikes) and human activities.
Man-made transients are generated by the switching of motors, transformers and certain types of lighting. In the past, this was not a common issue in residential installations.
However, with the rise of modern technologies such as electric vehicle chargers, air and ground-source heat pumps and speed-controlled washing machines, the likelihood of transients occurring in domestic installations has significantly increased.
Natural transient overvoltages are typically caused by indirect lightning strikes, often resulting from a direct strike on a nearby overhead power or telephone line. As a result, the transient overvoltage can travel along the overhead lines and the distributor’s network, potentially leading to severe damage to the electrical installation and equipment connected to it.
What are the different types of SPDs?
SPDs provide different functions and are classified as Type 1, Type 2 and Type 3 devices.
Type 1
Type 1 SPDs should be installed at the origin of the electrical installation located in or adjacent to the main distribution board. These devices deal with direct lightning strikes and are also used where structures have Lightning Protection Systems (LPS).
Type 1 SPDs, as shown in Fig 1, are used at the origin of an installation and in lines to or from structures originating beyond the area of protection afforded by the fitted LPS. Also known as equipotential bonding SPDs, Type 1 SPDs prevent dangerous sparking, averting fire or shock risks. It is important to note that LPS with only Type 1 SPDs fitted won’t protect sensitive equipment against failure. However, Type 1/2 combined units overcome this.
Type 2
Type 2 SPDs may be installed if the structure does not have an LPS fitted or does not require protection against direct lightning, see Fig 2.
Type 2 SPDs are used for indirect lightning effects and are known as surge arrestors. Where required, these may be installed at the origin, as well as at additional sub-distribution boards. This allows sensitive equipment within the installation to be adequately protected. Type 2 SPDs shall be coordinated with any Type 1 SPDs installed at origin.
Type 3
Type 3 SPDs shall be installed close to any sensitive equipment that requires protection, such as data/server racks and cabinets, see Fig 3. Type 3 SPDs shall be coordinated with Type 1 and/or Type 2 SPDs installed at the origin.
Regulation 443.4.1 requires that protection against transient overvoltages shall be provided where the consequence caused by overvoltage could result in:
- serious injury to, or loss of human life or
- significant financial loss or data loss
For all other cases, SPDs shall be fitted to protect against transient overvoltages unless the installation owner declines such protection and wishes to accept the risk of damage to both wiring and equipment as being tolerable.
Where the owner has declined SPD protection, it is important to record your recommendations for the protection against overvoltage. This can be done by using the NAPIT SPD Risk Declaration form, see Fig 4.
Conclusion
The decision to install SPDs ultimately lies with the customer, but they should be provided with clear information to make an informed choice about whether to install SPDs or not. This decision should consider safety risk factors and include a cost comparison, taking into account the cost of the SPDs.
This cost should be weighed against the value of the electrical installation and the equipment connected to it, such as computers, TVs and essential devices like smoke detectors and boiler controls.
Further information on SPDs can be found in the On-site Solutions publication available from NAPIT Direct.
Visit the NAPIT on-site solutions information page here
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