Transient overvoltages are significant increases in voltage that occur in fractions of a second and can cause devastating damage. But where do surges come from? Like with all threats, to manage them effectively it is vital to establish their origins. There are two main sources of transient overvoltages being the consequential impacts of lightning strikes (which can occur in excess of a kilometre away from the location of the surge); or through switching of sizeable loads be they transformers, large motors, light-rail systems, or through capacitive loads through the power supply.
Surge Performance Requirements
There are three surge protection device classifications: Class I, for protection against direct lightning currents (which is a lightning current arrestor) which activates based upon a 10/350 microsecond current profile. Class II, for protection against indirect lightning effects (which is installed ‘downstream’ from the lightning arrestor) and it is based upon an 8/20 microsecond current profile. Finally there is a Class III surge protection device which is designed for protection against switching overvoltages or localized surges, its performance is based upon a 1.2/50 microsecond and 8/20 microsecond current profile. Some devices can serve as a combined class I and class II device, but it is always important to clarify their performance.
Requirements to install:
As surge protection devices are directly incorporated into electrical circuits it is imperative that they are installed by a trained and competent person. Anyone lacking training and experience in working with electrical circuits should not attempt to install a surge protection device.
Preparation and installation:
Prior to any installation the circuit into which the surge protection device is being installed must be isolated and terminated at the mains. Working in an electrically live area is a potentially lethal hazard and should be avoided. Health and safety measures should be in place to prevent any surge protection device installation works occurring on live circuits. As the installation of a surge protection device is dependent upon the sort of device being installed it is not possible to provide any further information, beyond reasserting the need for all installations to follow the site and task specific installation method statement.