Explore the features of the Surge Protection Devices range:Devices have indicators to advise end of life of the device No resetting of SPD required, the excess voltage is quickly taken to earth, before the rest of the circuits are damaged The device meets the requirements of the IEC 61634-1 and EN 61643-11 standards The SPD enclosure can be fitted next to any exiting or new consumer unit of any brand where surge protection is required
The inclusion of Surge Protection Devices (SPDs) in the 17th edition of the BS EN 7671 Wiring Regulations amendment 1 shows how far the complexity and concern for personal safety of modern installation has come.
Two forms of surge
To be clear, SPDs do no protect an installation from lighting strikes, only a fitted lighting protection system to BS EN 62305 will prevent a direct strike from damaging the property. SPDs provide protection from two forms of surge:-
LEMP - Lighting Electro Magnetic Pulse
SEMP - Switching Electro Magnetic Pulse
What are surges?
Surges are short-term high voltage impulses often called ‘spikes’, ‘transients’ or ‘glitches’. The duration of these surges are typically measured in micro seconds.
Surges are typically produced from internal tripping events such as a lift motor in a hotel or office, lighting being turned on and off.
When there is a high energy inrush, this generates a surge and continues on around the circuits and can damage sensitive electronic equipment.
Lightning strikes also produce huge surges, up to 2km away from a direct strike. Surges can be induced in cabling systems, even when there is no direct connection to the point of a lightning strike.
The consequences of a surge
Without adequate protection the greatest consequence is a risk to human life, particularly in circumstances where medical equipment is involved and could be damaged.
Secondly, there is the potential downtime in production e.g. in a workshop, retail outlet or office.
Finally, there is the inconvenience of replacing valuable and sensitive equipment, insurance claims, and increased insurance premiums.
Note:- Currently, cabling for data, telephones and satellites are outside the scope of the 17th edition, but installers and specifiers should still consider providing surge protection for these systems.
Changes to the 17th Edition BS 7671 Wiring
Regulations amendment 1
Two specific sections of the regulations are pertinent to SPDs, and it is important to understand these in more detail:
Section 443 refers to why and when SPD’s should be fitted.
Is simply a risk assessment,and asks the question if not installing an SPD, represents an issue to human life, public service or industrial activity. If the answer is ‘Yes’ then fitting of the SPD is mandatory.
Where some confusion arises is the reference to risk of lightning in relation to the number of thunderstorm days per year. The UK on a whole has less than 25 thunderstorm days per year.
Therefore, it is not generally required to fit SPDs to all domestic properties.
However, where higher risk to personal injury or prevention of commercial activity, further risk assessment is required.
The main driver for installation of SPDs will be insurance companies, with the potential for reduced premiums if SPDs are fitted, or the possibility of non-payment of insurance in the event of any damage or injury if not fitted.
Section 534 refers to device selection.
Refers to how to divert the surge current to earth before this surge has a way to propagate about the wiring of the installation and cause damage, by considering which device to install.
A house or building is split into Lightning Protection Zones (LPZ), as a potential surge passes between one zone to another, this is where the appropriate SPD should be fitted, e.g. between the outside (LPZ0A) to the inside of a building (LPZ1) -SPD fitted in a consumer unit.
Areas where SPDs should be considered and further risk assessment required:
There are three types of SPD, called Type (or Class) 1, 2 and 3:
Installation as defined in the standard is simple enough, the device is connected with cables to and from the unit no longer than a metre in total, and a short path to earth will ensure the effective discharge of the surge to earth.
|Type 1||Type 2||Type 3|
|Used on building that has an overhead(TT) supply or a lighting protection system fitted on the roof||Suitable for all other installations at the incomer or after a type 1 SPD at sub distribution level.
The modern home with an underground cable supply would typically use a type 2 unit
|Used after a type 2 for localised over voltage protection in control cabinets or sensitive or valuable electronic equipment. E.g. A surge protected extension lead to a large plasma TV, is an example of a type 3 device|
Note: If a Type 2 SPD is installed and cable lengths are less than 10m, then there is no longer a requirement to fit Type 3 surge protected extension leads. If greater than 10m then type 3 surge protection should be fitted.
For the most part a simple two pole device for single phase TT or TNS will be enough. In TNCS systems a single pole unit may be sufficient as only the live conductor comes to the property that can bring a threat from outside influences affecting that supply.
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