Combining AC Voltage and DMX Control in One Cable

I don't think you'll have a problem at this low voltage...

1 - I assume that is 200 houses x (90x3W)fitting equals 54kW, when you work it out that's a lot of current, so voltage drops will be come significant if you go to 24V.

I'd guess that by the time you get bigger cable any gains in the cost of running the wiring will be slight.

2 - Realistically what will be the efficiency savings, after all each fitting is only 270W even a 10% gain is not much.

3 - Running the power and signals together is neat but it's probably cheaper to run 2 separate cables. you can use standard industrial power cable/fittings/junction boxes etc and standard shielded cable

4 - Doesn't DMX only support 32 devices?

The purpose of using 24 volt AC to supply the fixtures is to rate the entire system beyond the catwalk as low voltage. This means the cabling can run without conduit. The total ampacity is the same - but the electricians supply that power to the catwalk and stop there. This reduces project cost by more than $100,000. This also allows the lighting installer to place the lights anywhere in the ceiling space without regard to where the electricians may have placed the junction box with outlet.

Multiple 24 volt transformers will be readily accessible on the catwalk and reduce the cable lengths.

DMX is a 512 channel protocol. Depending on the type of fixture or dimmer, up to 512 devices can be controlled.

My primary concern with the design is the possibility of interference in the DMX signal caused by combining the 24V AC with the 5V DC DMX in the same cable.