The Model 29 contains avalanche
diodes, one for each line. All diodes are returned to a ground stud.
The Model 29 is provided with a 2-foot ground wire, male and female
DB9 connectors and supports RS-232 levels.
The Model 29 is a low cost solution to the problem of potential
equipment damage from induced transients on RS-232 com ports of PC
386/486 Pentium or laptops/notebook pc's.