TN7200 Relay Module can constitute a fire telephone system together with TN7000 Fire Telephone Control Panel, TN7100 Addressable Handset, TN7101 Fire Telephone Mobile Handset, TN7300 Addressable Fire Telephone Jack Socket and TN7301 Fire Telephone Jack Socket. Adding a relay at the end of the telephone bus can enhance the distance and quality of communication during on site construction