Roxburgh EMC, DVSB Surge Suppressor Unit 320 V ac, 420 V ac Maximum Voltage Rating 20kA Maximum Surge Current Lightning

Dual high-energy electrically isolated metal oxide varistors
Single and 3 phase line protection from surges and lightning
Modular design to snap-fit directly onto top hat profile DIN rails
Remote operation contacts for protection indication

Voltage surges, often referred to as spikes or transients are typically caused by switching of fluorescent lights, fuses blowing or nearby lightning activity. The worst voltage spikes are usually caused by lightning strikes and can reach up to 6000V, with current surges of over 3000A. The maximum size of the let-through voltage and current inrush depends on the location within the building's wiring system. BS7671: 2011 Amendment 1 Sections 443 and 534 cover risk assessment and provides guidance on protection of electronic equipment for installation engineers to follow. The fullest information on lightning and surge protection comes from the BSEN 62305 series of standards.