Existing doorbell transformer in 1950s era California house is sitting in open on a wood shelf in unfinished garage, supplied by non-metallic fabric-jacketed, plastic insulated 2-conductor cable in good physical condition. No ground, no conduit, no strapping, no junction box. I am replacing the transformer with a higher VA model for video doorbell, and wish to make the install better.
Replacement transformer will be mounted on knockout in a 4x4 metal junction box secured to framing, with existing 2-conductor ungrounded cable entering jbox via NM cable clamp. Because of cramped area in/around service panel, ground will be separately supplied to jbox via wire clamped on to Grounding Electrode Conductor.
Question: Can I extend this circuit from the new grounded jbox using metal conduit + THHN hot and neutral wires, or do new outlets supplied by extension have to have standard ground-with-conductors in same raceway all the way back to the service panel? That is, does the 2-wire + separate ground routing for the existing wiring from service panel to jbox prevent further extensions?
