I agree but didn’t know it was a Code requirement. IMHO, if you don’t know what you are doing at the disconnect, why are you opening it ? There’s a nameplate on the AC unit that states it’s a 240 v unit. Why would anyone assume the white wire in the disconnect was a neutral? Is the Code trying to protect or inform unqualified people who open a disconnect?
actually been required for some time, though I sort of disagree with the need for the rule for similar reasons you mentioned - if you don't know this is an ungrounded conductor you probably shouldn't be messing with it in the first place. I maybe can understand a little bit re-identifying it at the disconnect, but at the breaker panel end.... is obvious to anyone that knows what they are doing that if it is not landed on the grounded bus it probably is not a grounded conductor 99,99% of the time.
I once had 10-2 cable supplying a 120 volt water heater. Don't know why it was 120 volt, but that particular owner came up with abnormal things in his building. It was 40 or 50 gallon but actually come from factory as a 120 volt unit. Anyhow, when inspector was doing final he happened to notice I did not re-identify the white in the disconnect (line side, load side was colored conductors in flex) and proceeded to start marking it with his black marker. I told him it was a 120 volt unit, so technically he created a violation by doing that
It probably was low enough watts I could have run 12 AWG, and that might have prompted more questions from inspector, but it probably was a situation where I figured it would be the typical 4500 watt 240 volt unit and ran 10 AWG then when it showed up it was only 120 volts.