ABB OVR T2 unit is good for surge protection, unit is pluggable modular and can be easily replaced. ranges from 1.2 to 1.8Kv
The following info from ABB makes interesting reading.
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 surges are usually caused by lightning and can reach up to 6000V, with current surges of over 3000A. The maximum size of the voltage and current surges 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.[FONT=Arial, Verdana, Helvetica, sans-serif] [/FONT]
[FONT=Arial, Verdana, Helvetica, sans-serif]For over or under voltage, use a good AVR, or stabilizer, if you dont want to disconnect the supply every time there is a surge in voltage. I work in Africa and ensure all my boards are surge protected, this is due to the Lightning strikes to ground. Additionally the frequency of brown out and the prolonged dips caused by transmission switching causes more headaches than you can imagine. So everything is stabilized as well, with stabilizers that can operate up to 15% +- the supply voltage.[/FONT]