Surge Protection Devices

Protection against overvoltages of atmospheric origin or due to switching

What are surges and how are they produced?

Surges are short-term high voltage impulses, other names being, transients, glitches and spikes, these show themselves for a very short duration of time, typically some micro seconds.

Remember, it doesn’t need a direct lightning strike on an installation to cause damaging voltage surges – a ground strike in the near vicinity is quite sufficient. Also remember there are many other sources of voltage transients, such as the starting of large motors and the switching of large capacitive and inductive loads. Common examples of internal switching events are a lift motor in a hotel or fluorescent strip lights being turned on or off.

Regulation 443 (Updated 2022)

443.4.1 – Transient overvoltages due to the effects of indirect lightning strokes

Protection against transient overvoltages shall be provided where the consequence caused by overvoltage could result in…

(i) serious injury to, or loss of, human life

(ii) failure of a safety device, as defined in Part2

(iii) significant financial or data loss

For all other cases, protection against transient overvoltages shall be provided unless the owner of the installation declares it is not required due to any loss or damage being tolerable and they accept the risk of damage to equipment and any consequential loss.

443.4.2 – Transient overvoltages caused by equipment

Protection against overvoltages shall be considered in the case of equipment likely to produce switching overvoltages or disturbances exceeding the applicable rated impulse voltage of equipment according to Table 443.2.