Uninterruptible power supply (UPS) In the previous paragraphs, we discussed situations where the power supply can be lost or, at a minimum, endure voltage fluctuations. Today’s office electronic equipment operates well within certain design tolerances, but throw a power spike or a voltage sag to the system, and data can be lost. Think of a UPS as similar to a car’s cruise control. The car maintains a steady and continuous speed without your intervention, and the UPS maintains a steady and continuous flow of electricity even when power is lost.   There are two basic types of UPS: a standby off-line unit and an interactive on-line unit. The typical standby off-line unit is essentially a battery back-up system that is constantly charging. If power is lost, the system alerts you, the user, that you are now running on battery power. You will have enough time to shut down the system without losing your important data. This is both an efficient and inexpensive method for protecting your data.     The standby off-line unit is depicted Figure 1.  In this diagram, the transfer switch is in position to receive normal AC power (from your wall outlet) as its primary power supply (solid line). If the normal power is lost (from your wall outlet), the transfer switch operates using the battery supply. The battery supplies DC current (dotted line) to the inverter, which converts power back to AC current. The computer then operates off of the battery power supply for a limited period of time.   The second type, or most effective method, is the interactive on-line unit. With this unit, your normal office current feeds a charge/rectifier that then feeds the inverter and battery. If power is disrupted or lost, the battery then feeds the inverter and the system doesn’t even recognize the failure.     The interactive on-line UPS is depicted in Figure 2. In this diagram, the transfer switch is in position to receive normal AC power (from your wall outlet) as its primary power supply (solid line). Power doesn’t go immediately to the computer but is routed to the inverter, charging the battery supply, which powers the computer. If the normal power is lost (from your wall outlet), the transfer switch operates. The battery then continuously supplies DC current (dotted line) back to the inverter, which converts power back to AC current. The computer doesn’t recognize any change in power supply. It will operate on the battery power supply for a limited period of time.  Some interactive on-line UPS units can be purchased that, should the inverter fail, will allow for normal AC power to still flow to the computer.   As illustrated, each of these devices can and do provide protection against electronic and computer failures. But before you purchase any surge protector or UPS unit, check with a sales person at your local computer or electronics store, and consult with the equipment manufacturers for their input as well. Read products reviews and check consumer reports. Talk with other colleagues about their experiences and their suggestions. They can assist you with purchasing the correct equipment for your individual situation.   Do not ever forget to consult a qualified licensed electrician when you need to protect your office electrical systems. Remember— prevention of computer failures and data loss is possible through the use of a surge protector and UPS.