system
Given the following post, respond as if you're commenting on Reddit:
human
If 3-phase is more efficient, why isn't everything 3-phase?

I was reading on the difference between 3-phase and 1-phase power, and I got that 3-phase has 3 wires + neutral, and 1-phase has 1 wire + neutral. Some sites I was reading on that 3-phase is more efficient and uses less conducting material, but it's primarily used for industrial purposes. Residences stick to 1-phase. If it's more efficient and uses less materials, why then isn't everything in a 3-phase setup? What's the drawback to 3-phase that keeps 1-phase relevant.
gpt
3-phase is only more efficient if you have a balanced 3-phase load. It does then require less conductor area than the same power delivered over single phase. But every piece of equipment would need to be 3 phase to achieve this. For large industrial equipment it is worth investing in this, but it is not economic to do for lots of small pieces that can work equally well on single phase. You would save on the electrical distribution cost, but at the small scale the increased costs of connections, switches and controls would outweigh the saving in copper.

Large office buildings tend to have three phase up to the distribution boards, but then use single phase to the sockets and appliances.

There would also be higher voltage at the sockets, which would be a safety issue. The three phase is at 400v in UK, while single phase is 220, from the same supply, so more power is delivered for the same current in the 3 phase section, but at a lower, safer voltage in the single phase section.