+1 for RR
Residential:
Have 55+ in own house, built 1972, no failures. Some of the switches have gotten an oxide coating and needed replacing.
Class 2 24 v xfmr for control wiring, but added rectifier and 0.1 Farad capacitor bank so can drive all 55 relays at one time - all lights come on if alarm system tripped for example.
I put a relay in each light fixture, octagonal steel box. If you leave a loop of class 2 wire on the relay tower they are easy to changeout from the inside of the box (although have never had to replace an RR)
Prior to PC control circa 1980, used simple diode logic for relay control - any number of lights from any number of locations.
Ran surplus 50 pair telephone cable throughout house with 2 main panels that have control of every house light, used rotary switches and diode logic for selection.
After PCs came into being, was easy to build a parallel port interface for computer controls tht drive the relays.
As someone already said, the only houses I've seen like this were built/owned by aerospace EEs <G>
Commercial:
Large global company I retired from probably has millions of RR relays (and other larger types) in 100s of plants throughout the world, latest generation of controls allows a facilities engineer to see, on a laptop, the power draw condition of every/any plant/office and control the entire system as needed (obviously a well protected network).
