Clamping voltage - This tells you what voltage will cause the MOVs to conduct electricity to the ground line. A lower clamping voltage indicates better protection. There are three levels of protection in the UL rating -- 330 V, 400 V and 500 V. Generally, a clamping voltage more than 400 V is too high.
Energy absorption/dissipation - This rating, given in joules, tells you how much energy the surge protector can absorb before it fails. A higher number indicates greater protection. Look for a protector that is at least rated at 200 to 400 joules. For better protection, look for a rating of 600 joules or more.
Response time - Surge protectors don't kick in immediately; there is a very slight delay as they respond to the power surge. A longer response time tells you that your computer (or other equipment) will be exposed to the surge for a greater amount of time. Look for a surge protector that responds in less than one nanosecond.
Lower quality power bars with surge protection may cause as much as 20 to 30 dB of signal loss between their coaxial input and output. This can have a tremendous impact on the quality of your cable/satellite television signals. Look for power protection devices the have virtually no signal loss through their coaxial surge protection.
Intermediate power products offer power line conditioning in addition to surge protection. AC power line noise and noise generated by other electrical and electronic devices compromise the performance of home theater equipment. These disturbances can cause inferior picture quality flawed with video streaking, lower resolution and video bandwidth. From the audio perspective, power line pollution can cause dynamic distortion and loss of peak power. Power line conditioning removes this noise from the power line and maximizes the audio and video performance in the home theater.
More advanced power products also feature filters which deliver maximum current to high power components (such as amplifiers) and isolate audio equipment from video equipment. Each home theater component can add noise to the power line that can travel through your power bar or power protection device to other components plugged into it. Isolating audio and video equipment ensures that noise is not transferred between the components. Some devices even isolate analogue sources from digital sources plugged into them.
High-end power protection and conditioning products come equipped with voltage regulators or voltage stabilizers. Power coming from the wall outlet does not always measure exactly 120 volts. At peak power consumption times during the day, it probably measures closer to 115 volts whereas at night it might be closer to 125 volts. Devices with voltage regulators constantly measure the voltage on the power line. If the voltage dips below or goes over a specified range (for example between 88 volts and 130 volts) a voltage regulator will adjust the voltage to 120 volts.