Why Protect?


Electricians guide to the selection of mains surge protection devices according to the 18th wiring regulations (BS 7671:2018) and mains surge protection devices according to BS:EN 62305


Surge Protection requirements according to BS 7671:2018 18th Edition Wiring Regulations

Previously, the 17th Edition Wiring Regulations stated that the need for surge protection was determined by risk assessment.

Since 1 January 2019, according to BS 7671:2018 section 443.3, protection against transient overvoltages shall be provided where the consequence of damage caused by overvoltages meets certain criteria. If these criteria are not met, a risk assessment must be carried out to determine if surge protection is required. If a risk assessment is not carried out, surge protection must be installed.

This publication provides:

  • An overview of the requirements of the 18th Edition Wiring Regulations (BS 7671:2018)
  • A guide to the causes and coupling methods of transient overvoltages (aka surges)
  • Risk assessment guidance
  • Spacing requirements and installation good practice
  • Protector selection
  • Surge Protection Devices

Transient overvoltages (surges) are very short duration (milliseconds), high voltage (up to 6kV) ‘spikes’ caused by the secondary effects of lightning and electrical switching events.

“Surge Protection is designed to protect electronics from the effects of lightning and other transient overvoltages”

The probability of electronic systems being damaged by lightning is far greater than that of the building itself being struck, as lightning strikes up to 1km away from a building can damage electronics inside it. This is a far larger target area than the size of the building itself.

Damaging transient overvoltages are not only a result of lightning activity. Electrical switching, a common event, can also cause overvoltages which impair electrical components.

Surge Protection Fact 18th

The probability of electronic systems being damaged by lightning is far greater than that of the building itself being struck, as lightning strikes up to 1km away from a building can damage electronics inside it.”

As per BS 7671:2018, there is now a requirement to consider protection from damage caused by transient overvoltages.

Even in domestic settings, the effects of overvoltages can cause costly damage to equipment and fittings. Because of this risk, surge protection is a recommended step in adequately protecting a building and its contents, as the potential cost of replacing damaged installations and equipment far outweighs the cost of installing surge protection.

Given that electronic systems are a vital part of everyday life and have become increasingly miniaturised over the past decades, protecting them from surges is more important than ever. If they were left unprotected and damaged by a transient overvoltage this could result in major inconvenience, lack of service and potentially life-threatening situations.

Problems Caused by Transients

Problems caused by transients

This can range from burnt-out circuit boards to impaired operation of components.

Long term exposure to transients can result in invisible degradation of electrical components.

Disruption to the logic levels of the device rather than physical damage, resulting in data loss, software corruption and unexplained computer crashes.

Resulting from inoperative systems.

Transients can result in disruption to the electronic system, potentially causing data loss, software corruption and computer crashes. This can result in system downtime and consequential loss (equipment replacement, loss of service and revenue and labour costs).

A severe transient (15,400V according to IEC 60664) can result in serious damage to components and circuit boards. The damage can be obvious or difficult to pinpoint.

Long term exposure to transients (usually from switching) can result in degradation to electronic components, reducing system lifetime.

Effective protection against the damaging effects of transient overvoltages/surges can be achieved through installing Surge Protection Devices (SPDs).

There are three types of SPDs, specified depending on their intended location and other factors:

Type 1

Lightning Current Arrester

Install at MDBs to protect against lightning currents

Type 2

Surge Arrester

Install at MDBs and SDBs to protect against surge voltages and indirect lightning currents

Type 3

Fine Protection

Install less than 5m from critical, or high value, equipment for fine protection

Kingsmill supply combined Type 1+2 protectors, instead of Type 1 protectors, to ensure that the voltage protection level is below the withstand voltage for electrical/electronic equipment