Surge Suppressor Schematics
http://www.epanorama.net/documents/telecom/telesurge.html
http://www.epanorama.net/documents/wiring/surge_ac.html
http://www.tkk.fi/Misc/Electronics/circuits/rs232_protector.html
http://www.bb-elec.com/bb-elec/literature/232HSP.pdf