Surge Protection

Surges are generated when there is:

• A direct lighting strike
• An indirect lighting strike near the electrical installation
• A local switching operation in the power supply network, the switching of nearby high loads (like lifts or air conditioning equipment) or the tripping of protective devices

Direct lightning strikes cause massive destruction and often fires. Indirect strikes contain less energy than direct but can still result in the failure of data servers, heating controls, safety systems such as fire and intruder alarms and the building power supply itself.

An external lightning protection system is important. It protects people, property and against mechanical destruction and fire. However part of the current from a strike still flows into the building via the main earth bar (MEB) even though the rest is discharged to earth via the earth terminations.

Indirect lightning strikes, although the transient overvoltage is lower, can also cause a lot of damage. Such surge events include remote strikes to overhead lines or strikes near to the building or installation via the incoming electrical supply.

Equipment can be protected with surge protection devices (SPD) or arrestors. There are three types:

The types of surge arrester are as follows and a comprehensive protection system will include all three types:

• Type 1 - These should be installed as close to the electrical supply intake position. Type 1 SPD are used to use to protect other electrical or electronic services such as telephone, DSL (Digital Subscriber Lines) and broadband cable networks. This type is not enough to protect downstream devices such as distribution boards, machinery and computer equipment. They are capable of discharging any surge at least once.
• Type 2 – These are installed at each distribution board. Type 2 are used to prevent the spread of overvoltage within the electrical installation and protect each circuit load. They are capable of discharging a surge only once.
• Type 3 - These are used to supplement type 2 and are installed in parallel with, and used to protect, sensitive loads such as computers, printers and fire alarm panels. This type of SPD can be installed as part of a power strip thus protecting a number of local devices at once.

Specialist advice should be sought about selecting SPDs and their installation from a qualified electrical contractor and a member of ATLAS, or a chartered electrical engineer (see Lightning Protection guidance). The installation of SPDs must be undertaken by a qualified electrical contractor.