Is it required to ground a 120/240 1 phase subpanel to a main panel that is connected with armored cable(ac) within a house. ( It seems like it would be a good idea even if it is not required. I saw a similar thread that asked this question for a subpanel connected with EMT, and it seemed four wires were not required by code but were judged to be a good idea.

In a situation where a 3 wire ac was already installed connecting to the subpanel, what would you think about a seperate insulated ground wire run loose in the walls without conduit?

[This message has been edited by AC (edited 06-08-2002).]