130306-2035 EST
Virtually everyone around here has natural gas heat. Some new or remodeled homes have ground based heat pumps. Gas probably costs about 1/3 of electricity per unit of energy. I haven't checked this ratio lately, but gas has gone down some and electricity has risen a lot.
Visited my neighbors tonight. He is a former dean of public health (math, statistics --- still teaches) and she is a mechanic, nurse, and medical malpractice lawyer.
Their setup is an open delta, with a wild leg. Voltages 121, 122, and 217 relative to earth. The wild leg is a little high because of no loading at this time of year. House built in 1960. These neighbors are on a different primary than I am on. Gas heat, hot water, dryer, range top, and fire place are major gas energy loads.
Another neighbor is on my primary with 3 phase output, but I don't know the house location. This information was from a DTE serviceman when our last outage occurred.
First said neighbors have been using a Honda variable speed 7.5 kW portable gasoline generator, and a 6 circuit manual transfer switch. I use a 5 kW Honda portable. Their portable generator is a problem because they have to have someone else run it when they are traveling and power is lost. Their major needs are refrigeration, freezer, fish, heat, and a water pump for a fountain and cascading water path in the backyard. If the pump stops for a few minutes they lose about 1000 gallons of water into the street. When they are present then there are additional small loads required.
The big three phase air conditioner is not required under emergency conditions. The smaller air conditioner also can be classified as not required. It would be totally impractical to try to backup the three phase unit.
It does make sense to backup the entire house rather than just a few circuits. This can be done with a transfer switch to the 120-0-120 panel. Presently fused at 100 A. No mechanical problems to do this.
The size backup generator selected may determine how to handle the small air conditioner.
What initially surprised me was that two close neighbors to me had three phase in their homes. There may be more close by that I don't know about. Many houses in my area will date to the 50s and 60s, one to the 1860s, a mansion to the 1910s (Hoover ball bearing founder and owner, now a bank). So a wide variety of homes. Our whole area is three phase delta for the primary.
.