Absorption rating and clamping voltage: Absorption rating is the amount of energy that the protector can absorb before it fails. The rating is usually given in joules. For ideal results, go for a device with absorption rating of 700 joules or higher.
Clamping voltage is the voltage that triggers the protector. Go with a device with a lower clamping voltage. The voltage can be 400 volts or less. Certification: To have peace of mind that your devices are fully protected go for a protector that is certified by Underwriter’s Laboratories.