Lighting dimmers usually come with multiples of 3 lighting channels (3, 6, 9 etc.) in order to take advantage of 3 phase mains supply. Routing of 3 phase supply is usually internal to the dimmer, and there is usually an option for the single phase supply.
Lighting cans are usually of two types:
- 220v 1000W bulbs (par 64), which draw 4A current.
- 220v 500W bulbs (par 56), which draw 2A current.
So for 30amp 220v 3 phase supply, this means that each phase can give 30A of current. So on each single phase supply; there would be a maximum of 7 1000w par 64s or 14 500w par 56, or any combination of these up to a total of 30A. With a massive 21 1000w par 64s or 28 500w par 56s across all 3 phrases.
In the UK the 3 phase supplies in theatre installations etc. either large red 5 pin sockets where the 5 pins supply L1, L2, L3, N & Earth. Power outlet supplies in installations are seen as blue 3 pin sockets (L1 (L2 or L3), N & Earth).