We are into a job right now with just that problem, usually we first inspect the existing work, and determine if it needs repair or replacement, on existing work once the repairs are made we will, make sure everything on that branch, is working, and tested, if we suspect, other problems may exist. we will open anything in question, there are times, when replacement may be less expensive in the long term.
I do a lot. As it seems I am always hooking up existing, a small percentage of each job. (Permits for demolition here make a HUGE jump at 80%. 90% is almost 2X 79%, so there is almost always an existing wall or walls. Full structure demo is astronomical in demo permits!)
Must it meet Code? For the era when originally installed. I can't read the code for 1930, but I do know the last standard for most wiring methods is still in the code.
Must it be new or near new? Often 100+ years... K&T, black iron conduit, cloth covered wire, etc.
Must it be "safe"? Absolutely! No hacking from the past, no deteriation, etc.
Do you feel that if you modified it or added to it that you've in essence made it your own? (Yep, I go over it with a fine tooth comb, especially if previously modified, more so if modified during the 80's. (Bad era for the trades it seems. Lots of hack work.) I do own it, and will be inspected for its condition, based on original install standards, if I connect to, or re-connect it, or feed (if allowed) from it. (Can't feed from K&T.)
How do you deal with a call where a part of the existing system has failed? Failed? CB fails its gone... Insulation failed, it's gone. All elements in the chain of failure are gone. Those portions replaced new. If that amount justifies ALL new, so be it, it's my call.
[This message has been edited by e57 (edited 01-11-2006).]
Mark Heller "Well - I oughta....." -Jackie Gleason
Electure, Darned good call mate. As an ex-EC, I used to have this conflict of what I should do and what my Boss would have me do. As the Installing Electrician, the primary Inspection, matters the most. It is entirely up to that Electrician here if they want to connect into existing work. The up-shot of this, of course, is if the wiring that you "tap" into is bad, and it causes a fire, it's on your head. Personally, I run a circuit back to the panel, each and every time. I don't want to have to take on any more liability than what I should. IMO,some Electricians these days don't seem to take into account the effects of things like Voltage Drop and the length of circuit run as it applies to Protective Devices. These are the basics of the trade.