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[ The PC Guide | Systems and Components Reference Guide | Power | External Power | Uninterruptible Power Supplies | Parts of the Uninterruptible Power Supply ]

Main Power Switch

Most UPSes have a main control switch on the front panel of the unit. This is usually an electronic switch rather than a mechanical one; it sends a signal to the UPS's control unit, which tells it to turn on. While a simple affair, there are a couple of things to keep in mind about the main power switch.

The first is that this switch turns on and off the loads to the UPS, not the UPS itself. If you press the button to turn off the UPS, the equipment you are powering will immediately shut down, but the UPS itself remains powered, and charging the battery, as long as it is plugged in.

Main power switch of a consumer-grade APC UPS,
surrounded by four status LEDs.

The second thing to keep in mind is that this button needs to be protected from accidental (or mischievous) access. I have found that on many UPSes the position of the main switch is such that it can easily be pressed by accident. If this happens, of course, your equipment will shut down, negating the advantage the UPS provided in the first place. A better design would be to have the switch on the back of the unit, or have it protected with a cover. You can easily rig something yourself to protect a switch that is too easy to press, though it might be pretty ugly. :^)

Finally, if the UPS unit is not plugged in (for example, if it is being stored or transported) make sure the power is off and cannot be turned on by accident. Otherwise, the UPS will interpret the situation as being plugged in with the AC power off, and the batteries will be drained!

Next: Output Power Receptacles

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