The necessary energy to establish communication comes from the main supply.
Due to the especial materials used in these equipments, these types of telephones are manufactured to work under extreme conditions.
EXAMPLE OF AUTOMATIC TELEPHONE SYSTEMS
SWITCHBOARD
KX-TDA-30
Switchboard
TELEPHONES
EX-UE-F
Automatic telephone
EX-UE
Automatic telephone
EX-CJ-UE
Automatic telephone housed in watertight box
KX-TS-50
Automatic telephone
AUXILIARY ELEMENTS
EX-ACM-A
Headset with microphone and amplifier
CR-1
Relay box