CARRIER TAG: A data tag showing a 50-amp max breaker with a 31.4 minimum ampacity, which still allows a No. 10 circuit with a 75°C wire and termination rating. WIRE CONTACTOR: A wire and contactor displaying the 90°C rating on the wire and 75°C rating on the contactor (when properly torqued). NO. 10 ON A 50-A BREAKER: The data tag and the wiring of the air conditioner in Orr’s home, which includes a No. 10 wire on a 50-amp breaker. My first job in the trades was as an electrician’s apprentice doing tasks, such as pulling wire, building light fixtures, and moving scaffolding in grocery store renovations. I moved into HVACR and now serve as an HVACR contractor, instructor, and electrician. Growing up in a family surrounded by electricians, we were always discussing codes and theory around the house. Much of what I know came second-hand through my dad but also through Mike Holt, a well-known electrical author and instructor I now have the privilege of calling a friend. Over and over again, I have heard HVACR technicians and electricians quote rules of thumb regarding wiring sizing, and I have witnessed and participated in many heated debates on the topic. Before we get too deep in...