First off, the first electrician is wrong in saying that the use of a crimp-type terminal in house wiring is categorically unsafe. Crimp-type terminals listed under UL 486A for use on solid wire of the given gauge are considered acceptable for use in building wiring, as per UL 486A section 1.1:
These requirements cover pressure wire connectors and soldering lugs for use
with copper conductors according to the National Electrical Code, NFPA 70.
and NEC 110.14(A):
Terminals. Connection of conductors to terminal parts shall ensure a
thoroughly good connection without damaging the conductors and shall be made
by means of pressure connectors (including set-screw type), solder lugs, or
splices to flexible leads. Connection by means of wire-binding screws or studs
and nuts that have upturned lugs or the equivalent shall be permitted for 10
AWG or smaller conductors.
Terminals for more than one conductor and terminals used to connect aluminum
shall be so identified.
However, I would be quite hesitant to call this specific application fully Code-conformant -- garden-variety listed crimp terminals are listed for use with copper wire only, and it would be unlikely that the previous homeowner had access to terminals identified for use with aluminum wiring.
EDIT based on updated info about the devices:
Since the existing devices are copper only, your options go as follows (in order of preference):
- Find an electrician in your area who is qualified on the Tyco/AMP COPALUM system for pigtailing copper to aluminum -- these have a long, successful field service history, but require a specially qualified electrician to install, and are rather expensive -- you might be able to get the seller to shell out for this, though...
- Use the AlumiConn connectors with a torque screwdriver for pigtailing. This is something that most electricians can do, or you can DIY if you know your way around electricity and have a torque screwdriver -- the AlumiConn must be torqued to spec to meet its UL listing.
- Replace all the devices with modern CO/ALR types. This is a last resort as CO/ALR device performance has been historically variable, unfortunately.
My SOP is to do switches or outlets one by one, in the sequence I find convenient. I turn off the one circuit it's on.
And then I handle it as if it's energized. (Electrocution requires a path through your body, so you are particularly in danger if your body is also in contact with some other wire or object such as a pipe that is grounded) that would complete the circuit.) So aside from never touching a line conductor, I also make sure my body is touching no other thing, so even if I do bump an energized conductor, nothing happens. I'm not advocating working on energized equipment. I'm saying "belt and suspenders".
I discuss with everyone else in the house about what I'm doing, so they won't be messing with breakers or coming up and touching me and potentially "completing a circuit".
For identifying circuits, a few dollar-store night lights are convenient.
I don't get too formal with my work planning. I leave a marking behind saying "I've been there", piece of masking tape, etc.
As far as aluminum, there's "good" and "bad" aluminum. During postwar reconstruction (or in the US, a housing boom) there was a worldwide copper shortage, so they hastily made household wiring out of the AA-1300 alloys intended for transmission lines. Good conductor, but very bad mechanical characteristics at terminations. Aside from metal interactions, the stuff creeps, so it will "unspring" the force of a firm clamp. The industry fixed this in 1972 with a new alloy, AA-8000 series, specifically made for household wiring, marketed as such, so brazenly marked as such. These are legal today for new work. (NEC 310.14).
If it is not marked, it is a 1300 alloy.
Given the timing, your home might be using the new stuff so it's worth looking. If it is AA-8000 series, I would not rewire, just use parts or pigtails listed for CO-ALR. (Copper-Aluminum Revised; the old CU-AL standard proved insufficient.) There's a lot of scaremongering about aluminum wire, but it is only true for the 1300 series. Nonetheless, you'll take a hit on resale value even with 8000 for 8 AWG and smaller wire. AA-8000 is ok for the big stuff, 4 AWG and up.
With several million homes out there with the bad stuff, there are solutions to fix the termination problems - typically a pigtail, a special splice made to bind the 1300 series to a short length of copper for connection to the fixture proper. I would evaluate those.
Best Answer
Yeah, it looks like slow-cooked wires
The type of damage you have appears like the cable jackets have slow-cooked themselves from extended overheating due to overload. While properly terminated aluminum wiring is normally OK to keep around, the overheating damage means that the cause of the overheat/overload should be found/corrected, and the damaged cabling runs replaced outright.