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Protection and Backup

There are two basic forms of power protection equipment:

    • Surge Protectors
    • Uninterruptable Power Supply (UPS) - backups

Surge ProtectorSurge Protectors are designed to limit some high overvoltages (spikes) by absorbing them. In the most common type of surge protector, a surge or spike in voltage causes an electronic component called a metal-oxide varistor, or MOV, to divert the extra power into the ground wire.  When the voltage returns to normal this stops.  Most surge protectors also contain small chokes to help filter line noise (rapid up and down voltage).

One of the many things to judge a surge portector on is the joules rating. The rating of your average surge protector may be in the high hundreds to one thousand. The units with a higher level of protection can have a joules rating at several thousand. While there is no "industry defined" set number of a recommended joules rating to use, it's said that the higher the rating, the better the protection for your devices.

Once the capacity of a surge protector has been reached, it can no longer protect your equipment and should be replaced.  For a large spike, a surge suppressor will give up its life to protect your equipment.

Unfortunately, surge protectors can't supply the extra power that some equipment needs during undervoltages (sags and brownouts) or total loss of power.  This is an important limitation. What will happen to your computer or other equipment if you lose power?


Uninterruptible Power Supplies (UPS) are surge protectors plus a power backup.  They are designed to provide protection from both overvoltages and undervoltages.  They contain a battery and inverter to provide electricity to maintain or replace missing power from the normal supply. Depending on the unit, power ranges from 350VA to 2200VA (VA is volt-amps).

Standby Off-line UPS: In a standby off-line UPS, the battery and inverter backup supply is switched on in a fraction of a cycle when line voltage drops below a certain level. The transfer delay of power is around 25 milliseconds. This is the most basic and common type of UPS and generally cost the least. Some examples of this type of UPS can be seen here: Standby UPS

Line Interactive UPS: A Line Interactive UPS is the middle level of UPS and has a power transfer delay of around 5 milliseconds. These power units work with the AC power lines to smooth out waveforms and compensate for slight rises and falls of voltages. Some examples of this type of UPS can be seen here: Line Interactive UPS

Online UPS: An Online UPS is the highest level of protection and as such, usually has the highest cost. With these units, power is always supplied through the inverter. During a dip or loss in power, the battery fills in whatever power is needed. Equipment that is sensitive to transients, noise or cannot tolerate power interruptions may require this type of UPS. This type typically costs more and uses more power. Some examples of this type of UPS can be seen here: Online UPS