Usually, jargon from a technical field is unintelligible to people outside of that field. that is bad enough and is often avoidable. In this case, the jargon is misleading. That makes it unusual. Now, if everyone would call it "split phase 120/240" or something like that instead of single-phase, it would be much more satisfying. What makes it really frustrating is that when I have asked, probably a dozen or more times over so many years, why typical residential power is not two-phase, I get dismissive answers. Maybe the answers came mostly from people that I thought would understand more than I do, but really don't and don't want to admit it. I just thought of another point for the philosopher-engineers to critique as I re-read the previous posts. I have single phase power at my house (well, most people do) when connected to the POCO. That is because the power originates from a single winding on a generator. When the power goes off and I fire up my back-up generator, I have is two-phase. Is that correct?

You haven't supplied enough information for a definite answer. There are many different models of transfer switch, and several ways said switch could be installed. A picture of the area and specifics about your switch would help. Be aware that there is often a requirement that equipment be installed "in accordance with manufacturer instructions" which if strictly interpreted (not likely) in your case means the switch must go "...18" on either side of the load center...". Will your new transfer switch become the service disconnect? If so, it should be "readily accessable" and if it ends up so low that you almost stand on your head some inspectors might not pass it. You say everything is "crowded together"- so working clearance could be an issue, too. Speaking of inspections, are you going to have one???- if not you can probably put it where ever you want to. I have seen transfer switches that required a ladder to throw and some 12" off the floor. And THANK YOU for your decision to use a transfer switch, and not some cobbled together cord, wire or circuit breaker trick.

These manual transfer switches use the breaker in the transfer switch when using generator power. Those breakers are not (can not be) AFCI because there is a single neutral from the transfer switch which lands on the neutral bar of the main panel. An AFCI breaker has the neutral coming back from the load and then in normal operation out of the breaker to the neutral bar. Because of this, you can't have AFCI's in a load side transfer switch because you would have to switch the neutrals and the hots. An AFCI needs power to trip, so when your utility power is off, the circuit works because the hot is fed by the generator and the neutral flows from the load to the AFCI breaker in the panel and then to the neutral bar. When utility power is restored, the AFCI is powered and it detects a fault condition because it sees a major imbalance between hot (which it can't detect because it is coming from the generator) and neutral. It is now able to trip since it is powered, and it does.

There is NO restriction to panels in closets. There IS a restriction to panels in closets with easily ignitible material, such as clothes closets. A utility closet is perfectly fine, and quite typical. John, your clearance dimensions are way off. First thing, there is NO 66" rule. You can have the center of the highest breaker handle as high as 6'7". The clearances are 30" wide (centering is NOT necessary), 36" in front, and 6'6" high.