Greetings, I'm an Electrician in Chicago, typically working on new commercial construction. I'm currently working on a project at my own house that I may be overthinking or misunderstanding entirely. This is of course residential and the house was built in the late 1970s. The service to the dwelling is 2/0 Al. USE which is feeding an old Square D panel with an 100A main OCPD. I'm looking to replace the panel with a new Square D QO, and if I can have a little more headroom without running a new service that would be ideal.
Where I'm getting hung up is I assume USE-2 wasn't around in the 1970s, so my intention is to use the 75° column in 310.16 for 2/0 Al. USE which provides an allowable ampacity of 135A. Since I don't have a definitive load calculation it would seem logical to round down to a 125A main OCPD and ensure the breaker protects the conductor.
This seems like sound logic to me, but I'm sure others on here with more experience can weigh in on this.
Where I'm getting hung up is I assume USE-2 wasn't around in the 1970s, so my intention is to use the 75° column in 310.16 for 2/0 Al. USE which provides an allowable ampacity of 135A. Since I don't have a definitive load calculation it would seem logical to round down to a 125A main OCPD and ensure the breaker protects the conductor.
This seems like sound logic to me, but I'm sure others on here with more experience can weigh in on this.