The official "Installation Manual" is technically correct, but it suffers from the same flaw as most legacy intercom systems: No voltage drop over 50 meters of CAT5e. No existing wiring from a dead competitor (like Samsung or Panasonic). No plaster dust in the terminals.

If you are holding a Commax DP-RA01 (often part of the DRC-4 or DRC-4K family of video door phones), you have likely already done two things: 1) Opened the box, and 2) Googled furiously for a PDF that isn't buried in a Korean server.

The RA01 is a robust piece of Korean engineering, but it is unforgiving of amateur wiring. Treat the installation like low-voltage telecom work: meter everything, twist and tin your wires, and always add that termination resistor. Your 3 AM self will thank you.