How an Ordinary Surge Suppressor Works

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(Mode 2 operation)
Ordinary surge protectors (and UPSs) simply divert harmful surge current from the hot line to the neutral and ground wires, in a process usually described as "all three modes of protection." Any surge suppressor which diverts surges to the ground wire is a Mode 2 suppressor.

The hot line is the only source of dangerous external surges since neutral and ground are bonded together and fastened to an earth rod at every service entrance.

Unfortunately, this "three mode protection" process diverts high energy powerline surges directly into delicate low voltage audio, video and computer datalines, because these lines use the powerline ground wire circuit for their reference voltage.

Computers with modems or datalines to other equipment, such as LANs and shared printers, should never use Mode 2 surge protectors which divert surges to the powerline ground, because this will increase the likelihood of damage.

A surge which is not diverted by a surge "protector" will hit the computer's power supply, which is considerably more surge tolerant than the delicate dataline circuitry that Mode 2 suppressors endanger.