Originally posted by: PlasmaBomb
Why not just use a surge protector for most things? I can understand a UPS for a computer you are working on, and don't want a power outage to reek havoc...
Voltage spikes are only one form of damaging fault. How often these occur depends on your location, frequency of lightning strikes, type of power drop (overhead or underground), etc. I've never seen a damaging power spike either at home, school or work. But if you have overhead power service, or you have pole mounted transformers near by, then you are at higher risk of spike due to lightning.
Under and over-voltage faults are other causes of equipment failure.
Over voltage faults are uncommon, they are typically caused by a serious short circuit in the opposite phase (in a split phase drop), or an adjacent phase (in a 3 phase service, or where you receive a single phase from a 3 phase transformer). Even then, the degree of overvoltage is likely to be modest and should be within most equipment's tolerance unless the fault is very severe (e.g. an industrial customer supplied from the same transformer) or very close (e.g. you short your 70 A tankless water heater supply to neutral).
Undervoltage is more common, and has many causes, usually related to overload, poor connections, or a power grid fault. Although it sounds counter intuitive, electronic power supplies operate at considerably higher stress under low voltage conditions (this is because they automatically increase their current draw as voltage drops, to ensure a constant output). This is particularly the case with 'universal PSUs' or those with active PFC. Brownouts that drop voltage to 80V can cause overheating and serious damage to these PSUs. Other equipment that may be damaged by brownouts include compressors (e.g. fridges, AC, air compressors).
If you want to protect against over and undervoltage, then a surge protector is unlikely to help. There may be some benefit with over voltage situations, but surge protectors are not designed to protect against this, and will likely burn out, and/or trip a breaker.
The advantage of a UPS is that it includes modest surge protection while also protecting against under and overvoltage. Even the cheapest will do this, although they will drop to battery mode in both of these conditions. More fancy 'line interactive' ones will adjust the mains voltage as required (without resorting to battery mode during fault conditions).
