This has been a matter of much discussion and debate, since the wording was added into the NEC about the metalic raceway requirement to the first device to protect (AFCI) downstream.
Opinions were tilted to the installation AFCI, where required (additions) via installing a subpanel, utilizing a metalic wiring method to 'satisfy' the wording. However, further debate could not substantiate the requirement for metalic wiring method for the subpanel.
The accepted solution resulted in an Article 300 wiring method feeding a subpanel, and AFCI from that sub.
A lot of us are wondering why that wording is within the NEC, when no device is available.
