When are you required to upgrade wiring?

I did a house yesterday with a significant addition. Of course the addition had all new wiring. The SE panel (in the old part of the house) was new and all the wiring in the panel was new. But the old part of the house, including the kitchen outlets, still had the original 2 wire circuits (flexible armored cable). The old part of the house had been completely remodeled, but they left the wiring the same (1949 house).

When would the AHJ require existing wiring to be upgraded?

Usually when there is a significant re-model the electrical system is required to be brought up to the current code, but each AHJ may have a different view.

Remember, the code is not a law, but a reasoned suggestion or guideline for safety. The AHJ is not necessarily required to follow any “code” other than what has been adopted by the local jurisdiction.