How do you properly transition from K and T to romex if you have to and you aren’t able to get back to the panel?
I would use
any means possible to get a new run before adding to K&T.
That said, one consideration is to remember there is no ground wire, so any additional wiring to a receptacle would need to be GFI protected and marked as "No Ground". The same as required for any change from a 2 pronged to 3 pronged receptacle. 406.4(D)(2)
Another consideration before even thinking or starting to run an extension of a K&T is most times the circuit has already been added to and in some cases multiple times, so may present an overloading situation.
Thirdly, need to confirm the neutral line at any splice point, when K&T was used concern for polarity was almost non existent. I've come across energized outer ring on lighting receptacles, a clear safety concern.
Lastly, or more appropriate firstly, consideration for AFCI requirements in 210.12(D) would seem to make adding on to K&T non compliant, not sure of ground connection for proper operation of an AFCI receptacle, and not aware of a duel rated receptacle that would be AFCI/GFCI, as adding to such a circuit also requires GFCI receptacle installed and marked per 406.4(D)(2)(b) with additional consideration as informational note 2 of section references additional requirements found in 250.114 about grounding conductor requirements.
One last thought, not code related, that once you touch that circuit, YOU become from one perspective, liable for the entire circuit not just part touched or added to. Any failure that results in damage or injury YOU or your installation would be looked to as a probable cause, and would need to defend your work. We are living at a very litigious time were attorneys will be looking for anyone to blame and sue. That may be the biggest reason many would not add to a K&T circuit, but insist on replacing, even if they could meet all other aspects of code to be able to add on.
