DoorBird D21 Série Manuel D'installation page 20

Please take care when connecting the cables and wires. Connecting
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the cables and wires the wrong way may damage the device. Wires
without insolation material must not protrude out of the green screw
connection terminal, it may lead to electrical short and damage the
device.
The yellow, green, and red cables that lead out from the side of the
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Main Electrical Unit must only be used to connect components
certified by Bird Home Automation.
20
Switching relay, max. 1-24 V DC/V AC, 1 Ampere.
The relay contact can be used to connect a conventional
door chime.
Additional feature: The switching relay blocks
temporarily if a visitor keeps the call button
pressed permanently.
The power supply for the door chime must be installed
separately. Should you have any questions, please contact
the manufacturer of your door chime. You can find
compatible door chimes at www.doorbird.com/support
Some door chimes operate with
110-240 V DC/V AC. Do not connect such
door chimes to this relay contact. The device
is immediately destroyed and life-threatening
injuries can occur.