Posted by:
Mnemonic
(
)
Date: June 24, 2011 02:54PM
The answer is not as simple as yes or no.
Generally speaking, a device plugged into a surge suppressor is protected from voltage spikes. This protection is provided by a filter circuit consisting of inductors, capacitors, and metal-oxide varisters (MOV). The MOV is a component who's resistance varies with the voltage across it. For lower voltages, it's resistance is very high. As the voltage increases, there comes a point where it's resistance drops dramatically. These devices are placed across the power lines inside the suppressor so that any voltage spike in excess of the trigger voltage is shorted. This keeps the surge from reaching the devices plugged into the surge suppressor. Surge suppressors are rated in the number of Joules of energy they are designed to absorb without being damaged.
Turning the surge suppressor off added another layer of protection by creating an open circuit between the power coming into the suppressor and the circuitry inside it. This will generally increase the protection of the devices plugged into the suppressor but not completely. If enough voltage is applied it can arc across the open switch and into the attached devices. The same is true of the devices plugged into the suppressor. If they are turned off they are protected by the open circuit of their switch. However, a large enough voltage spike can arc across the switch and cause damage.
Here are the levels of protection in ascending order.
1. Device plugged into a surge suppressor that is turned on.
2. Device plugged into a surge suppressor that is turned off.
3. Device plugged into a surge suppressor that is unplugged.
4. Device unplugged.
5. Device unplugged and wrapped in a conductive material like aluminum foil.
Uninterruptible Power Supplies (UPS) add another level of protection by protecting your devices from low voltages or voltage sags in addition to voltage surges.
Additional reading:
http://en.wikipedia.org/wiki/Varistor