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> ...the copper to run those is extremely expensive, on the order of hundreds of dollars. Adding an additional wire may add an additional hundred dollars or more...

Vs. checking a couple commodity pricing web sites - copper is currently ~$3.85 per pound.

I really doubt the motor of any "residential" HVAC unit is heavy enough for that "hundreds of dollars" to actually pan out...

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I'm referring to the cost of the wiring, not raw copper stock price. Also, I mean the cost of the wire from the breaker panel to the HVAC unit. On average, I'd assume that the wire run is at least 50 feet. 100 feet wouldn't be unusual. 100 feet of single-wire 10 gauge THHN (enough to run most HVAC units here) would be ~$60. That also doesn't include any additional cost by upsizing certain things (conduit) that may add.

To note, as mentioned, copper is not the only cost here. You also need another pole to your breaker, which adds cost. Plus busbar upgrades. And more.

3 phases is cheaper than single line for delivering a houses power. You can get away with 3 smaller cables than the larger cables needed for 110V or 230V low voltage single phase at a particular amperage.

The cost of termination of 3 phases is insignificant compared to the cost of the rest of an electrical system in a modern home.

It’s the better system.

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