Quote Originally Posted by 12vdc View Post
It will protect only line-to-line surges. Remember, lightning seeks its path to the nearest earth. The job of the arrester is to divert this discharge path to the ground. If you dont have proper ground it will seek its path to whatever device connected to the ingress media(AC mains, cable or telephone service drop, antennae) every electronics plugged to it is a potential path for discharge point - could be the nearest chasis, a damp floor, or a humid air.

Newer buildings comes grounding as standard. Maybe the outlet isnt but the mains circuit breaker box should have it as a provision if ever you decide to install one. The old house, i had to install ground rods and wires to the powerplant, water pumps & heater, the breaker box, server cabinet, and kitchen electric appliances..
if the house has no provision for a grounding line, it would be safer if i can directly ground the ups by earthing it to metal rod?