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Applying Surge Protection

Applying Surge Protection

In a well-designed system, it is important that for each building, both the incoming and outgoing circuits are protected by surge protection devices (where the cables enter and exit the building).

This includes:

  • Mains power supplies – including UPS
  • Telephone lines
  • Data communication lines
  • Instrumentation, control, signalling lines
  • Coaxial lines for CCTV, TV, & antenna cables

Field based electronic equipment also need to be protected.

All power, data and telephone lines should be bonded to the main earthing bar in the structure. The live conductors of these services must be equipotentially bonded by an SPD, at the point where the service enters the structure.

Should the BS:EN 62305-2 risk assessment dictate that a Structural Lightning Protection System (LPS) is required, the system designer should always fit equipotential bonding Surge Protection Devices (SPDs). These are referred to as Lightning Current Arresters in our product selection pages.

If the assessment dictates that structural lightning protection is not required, but there is an indirect risk that electrical services entering the structure could be affected, then the designer should always fit Surge Protection Devices.

A lightning protection system that employs the use of “equipotential bonding SPDs or lightning current arrestors” alone, does not effectively protect electronic systems.

Additional protection is also required if equipment is located more than 10m away from the location of the first upstream SPD. The purpose of this is to protect electronic systems from internally generated transients, as well as from transients that have become magnified (through oscillation), due to travelling long distances (over 10m) from the upstream SPDs. See section on Recommended Protective Distances (pages SPD:20 – 22) and figures SPD:10 – 12.

Effective protection is only achieved through the use of “coordinated SPDs” – in other words, a set of SPDs installed in a cascade, such that service entrance/lightning current SPDs and equipment protection/surge arrester SPDs compliment each other. The combination of both lightning current and surge arrester products, in different locations is what provides effective protection. Coordination becomes vital where transient overvoltages need to be controlled downstream of the service entrance position.

Protector coordination is detailed on page SPD:92.

There are three types of SPD. They are classified according to the location in which they are installed:

Type 1 Lightning Current Arresters
Location:Boundary of LPZ0 and LPZ1 - where lightning current could enter a building or structure
Power:Type 1 - lightning current arresters (tested with a 10/350µs waveform)
Data:Category D
Type 2 Surge Arresters
Location:Boundary of LPZ1 and LPZ2 - protecting from internally induced transients (switching and the effects of oscillation over 10m) as well as the indirect effects of lightning
Power:Type 2 - surge arresters (tested with an 8/20µs waveform)
Data:Category C1
Type 3 Surge Arresters
Location:Boundary of LPZ2 and LPZ3 - typically installed next to the equipment being protected, serving as “fine protection”
Power:Type 3 - surge arresters - fine protection (tested with an 8/20µs waveform)
Data:Category C2
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