I have the All-New Ring Doorbell 2020 release and an older (~1995-6) Nutone IM 4006 series (whole house) intercom system with one front door doorbell/intercom. I wanted to perform a hard wire installation of my Ring Video Doorbell to replace a defective front door doorbell/intercom.
The key (but unoriginal) concept for this installation was to: “replace” the front doorbell button which activates the Chime module within the intercom system master station with a relay switch (see the wire diagram).
(1) I turned off the circuit breaker to my intercom system.
(2) I repurposed the two front door intercom wires running from the “Terminal Board” at the back of the Nutone master station because they run from the station to the front door.
(3) I connected a wire from one terminal of the 16VAC transformer to the low voltage input coil from the relay and attached the other end of the low voltage input coil from the relay to one of the repurposed front door intercom wires that ran to the front door. I connected this repurposed wire to a Ring Doorbell terminal.
(4) I attached the second repurposed front door intercom wire to the second transformer terminal and attached that wire at the front door on the second Ring Doorbell terminal.
(5) Finally, I used a wire to connect one of the normally open switch terminals on the relay to the (common) COMM terminal on the Nutone Chime module (after detaching the old connection) and I used a second wire to connect the other normally open terminal on the relay to the (front door) FRONT terminal on the Nutone Chime module (again after detaching the old connection).
(6) Turned back on the circuit breaker to the intercom system and performed an In-home Chime Setting as directed using the Ring app.
The Ring doorbell maintains charge and work just find. The old doorbell wires were left unattached (cap them if it makes you feel good).
Note: Picking the right relay can be tricky because my system runs off a single Nutone 105T, AC transformer (16VAC @ 15 watts) and I did not want to replace it or install a second transformer. After some online research, I found two choices that seemed reasonable: a 24VAC relay -_uxcell A14071800ux0297 35mm DIN Rail DPDT 8P General Purpose Power Relay AC 24V Coil W Socket or a RIBU1C Enclosed Relay (10 Amp SPDT with 10-30 Vac/dc/120 Vac Coil) from Functional Devices, Inc. Tried both but the uxcell 24VAC relay seemed to work better in my hands. See my wire diagram. _ The Ring Doorbell activates the relay which activates the Chime module and I hear the doorbell chime throughout the whole house as before.
The front doorbell/speaker wall box is large with this Nutone intercom system. I found an appropriate cover plate from Kyle Switch Plates (https://www.kyleswitchplates.com) to cover this relatively large doorbell/speaker wall box. It was used to mount the Ring doorbell.