sorry, seems like I always ask questions in multiples of 2 or 3 here... I saw an old 200-amp panel yesterday which had a 12-awg Cu "tapped" off of themain lug, stuffed into the mainlug with the Alum. 4/0... it exited the panel through a short nipple into a small subpanel next to it and was used for exit lights, or at least thats what was written next to the breaker. First, this isn't ok even for an emergency type circuit is it? My understanding is that to tap, first you need to start from an OCPD in one panel and then connect the tap in a j-box and end up with the tap having an OCPD where it ends also. Second, was this possibly ok in a previous code... it had the old pushbutton breakers but the subpanel used probably 70's vintage breakers, so guessing this was done in the 60's or 70's, I don't know breakers and panels that well to date them. [no pun intended, you know hwhat i mean] And what about Cu anmd Al wires in the same lug? Would you go back to the owners of this sorority house and suggest they have this fixed, or are there any significant dangers here? By the way i saw an older church once that had the same set-up, emergency lighting panel tapped off the main lug, so guess this must be the way it had been done in the past.
thanks, C

Cindy,
OK, I'll start the argument. What you're seeing used to be a standard way of supplying emergency lighting. It does comply with 230-2(a)(2). That said, it does NOT comply with a bunch of others, Article 110 states you can only put one wire under 1 lug (compliance with UL rating) and likely the lug you see, and the ones we all used to "stuff" 'em under, aren't rated for it. It would not take long to compile several others. Likely, what you are looking at was inspected and judged fine at the time.

What actually is wrong with the installation ? With literally thousands and thousands on line with no problem, not a lot.....except, if some 1/2 electrician 'pokes' around in there, they may not notice the #12 wires which are unfused and do something dumb with them. My bet is if you had all the accident reports in front of you caused by such installations, it was someone who had absolutely no business in there to begin with, but just like the "not to be taken orally" on the Prepartation H, we are geared to protect some moron from himself. Since we no longer provide a true emergency service in these small installations, we have to use battery packs, so maybe it's a giant conspiracy from Eveready, or Ray-O-Vac eh ?

There was a long time we used to run the #10's or 12's out to the meter buss as well, but the power companies (at least Locally) stopped that practice as well, back to my conspiracy theory.

Again, likely you are looking at an installation that was judged in compliance at the time, so it probably grandfathers. Hope this helps

Just for the record, I have an old '59 code book, and its 110-13 had wording to the effect that it was a no-no to mix aluminum and copper, and "..terminals for more than one conductor shall be of a type approved for the purpose.' So I have some doubt that the 'grandfather' hypothesis would hold.