Determine whether hard wired or plug-in type units are appropriate. Hard wired units have multiple, large MOVs to divert excess current and absorb more energy at higher clamping levels than plug-in types. Select the failure mode of the protection device. Decide on the level protection and if failure does occur, whether it is permissible to have an outage without protection. Some suppressors have both visual and audible alarms.
Some suppressors also have circuit breakers or fuses to protect circuits from normal overload.
Listed - Look for the UL 1449 listing, not just UL 1449 tested. Under UL 1449, surge suppressors are required to pass three durability tests that determine the performance of the device. Energy Specifications - Make sure the maximum impulse energy the suppressor can withstand is specified on the suppressor in joules. Noise Attenuation - Look for the type of noise attenuation capabilities of the device. For example, some devices have both transverse and common mode noise attenuation capabilities.