What is the majority of the INTERIOR wiring in your (client's) electrical system?

Copper
Aluminum
Both/it depends

Unless it's an older facility, I would think the answer would be Copper. This will be interesting.

Not really...even with older facilities the only time that aluminum became popular was for a short period of time when the price of copper relative to aluminum got aluminum to fall into favor. However the alloy used wasn't really ideal for the purpose so hence we had a number of failures and aluminum got a very bad reputation. Today there are aluminum alloys intended for electrical use that fixed almost all the problems except the nagging one that copper and aluminum can't be mixed, at least not in direct contact. Copper has a significantly lower resistance and thus significantly higher ampacity, enough that in most cases smaller gauges can be used so the overall cost of the cable is lower. I've encountered aluminum wiring aside from a few residential/commercial areas in an old plant in New Jersey once where some of the feeders used aluminum. We knew about it because we had several failures but the issue was clearly poor installation. Many times you'd find a split bolt connection lugging copper directly to aluminum with predictable results (copper is eaten by aluminum galvanic cell). Simply installing the proper (CuAl) connectors and spraying NoAlox on the exposed cable took care of the problem for the most part. Ultimately it was the wrong alloy though so eventually it needs to be replaced.

And Jim had the right idea by limiting it to indoor wiring. If you asked a lineman what he/she thinks of copper wiring, you'd get just the opposite answer. As an example a Mastec crew was replacing an old copper overhead line a couple years ago here. The copper line snapped in half which they quite often do when the lineman lifted it off the insulator. The energized end fell to the ground but fell in a way where it glanced off a ground man' s shoulder, severely injuring him. Most of the copper cabling in this area has become extremely brittle over time. I've never seen this happen with AAC (all aluminum conductor) or ACSR (aluminum coated steel reinforced) though and as far as I know there's no upper limit on it's usable lifespan.

More recently I've noticed from some of the reports that it needs to be considered for incident energy reasons. Aside from higher impedance, aluminum boxes and cabling does affect incident energy.

Most of the inferior wiring that I have seen is mostly where the conductor is too large for the breaker lugs and a "haircut" is given to the conductor.

What I see much more often, particularly in older facilities is overdutied breakers.

It depends on several things, including the designer's ideas about aluminum. In 45 years of work, I've seen a failures of both copper and aluminum, however, they've both been rare. And the failures were not necessarily caused by the wire, but by poor terminations.

Power companies have used insulated aluminum conductors between their secondary and the client's meter for years. There are several reasons they've gone to aluminum including the weight of copper, the cost and of course, theft. Those pushed power companies away for copper wire toward aluminum. And all they needed to do was improve their termination standards. Because of that, they've had very low failure rates. And with our local utilities, they often pull the 3 phases and the neutral in separate conduits.

On the customer side of the meter, we see mostly copper, but that's changing. In the 70's and 80's, aluminum had gotten a bad reputation. There was nothing wrong with the wire, it was the people terminating the wire as well as the terminations. One other factor, electricians like using copper and contractors are often electricians and they've not really thought about the value of aluminum over copper. Once they do, they realize each product has its place.

I have never seen aluminum wiring in a plant unless it was larger sizes, even then it has been rare.

I have been blessed with aluminum wiring in my house. Built in the early 70's, all the houses in my neighborhood are wired in aluminum. I have pig tailed my entire house with copper tails but I have lost a receptacle or two and had one switch where the wire was wrapped around the screw (not completely) and came out from under the screw and was laying on the head of the screw. The wire has never been the issue (except it is brittle), it is always the connection. I have used up a 2oz bottle of NO-OX just in my house!

I had a neighbor years ago call my about a "hot wall". After investigation I found the bathroom light switch connection had burned the insulation back 2 inches and the wall was indeed warm all the way to the ceiling.

I just realized one other place that is almost exclusively aluminum. For the most part the majority of oil filled transformers in the U.S. today are aluminum coils. In the open pit mining industry where the "aluminum stigma" is alive and well, ordering transformers with anything but aluminum coils automatically makes it a "custom" transformer even if everything else is specified close to one of the existing standard designs.

We have been seeing aluminum more and more so much so that in lieu of it being a VE by the contractor, when the project is started this is a conversation with the owner if they are open to the idea it becomes a required bid alternate at bid time, we have found if it comes in as a VE after the contract is awarded it is likely the owner will see a credit although not the same credit you would see under a competitive bid scenario. We see it specified / used in all facilities, from commercial to heavy industrial. Most of the automotive facilities [factories] have standardized on AL IAC in tray for bus duct, etc. Some will even use triplex-Tray Rated AL [XHHW-2] spaced to achieve the free air rating in tray, and most contractors will procure the cable from the distributor this way using colored insulation and pre-plexed on the spool with pulling heads already attached as to make the installation less labor intensive as a way to “sharpen their pencils�, in commercial buildings even the use of riser MC-AL. In most applications we see it limited to 100A and above, some down as far as 60A. As for the lugs not sure if “trimming the hair� is the right approach [I believe there was an article about this in a recent EC&M an investigative article], just being sure when you procure the equipment or are checking submittals/shop drawings you are getting the correct lug kit. Most breaker and panel manufacturers will have more than the standard lug kit available, or you could always utilize aluminum to copper pin-adapters, where lug size or the requirement for copper cable at the termination is an issue [some HVAC / mechanical equipment]. We have found as long as you have a good contractor competent in the requirements for the termination of aluminum cable there have been no issues, some owner allow the use of AL cable with the exception that all terminations are Cu using the associated Al-Cu pin adapters. The one place we have not seen allot of aluminum is in the MV world, still mostly copper EPR or sometimes XLP, however it is changing more and more.

I'll be more blunt. It is not only a Code violation but a safety violation for five reasons:

1. The ampacity is gone. If you have a cable with a certain amount of cross sectional area and you go and trim away part of the cable, guess what it isn't anymore?
2. Ever heard of "alpha spots"? At a joint contrary to popular belief only a small fraction of the available surface area in contact actually conducts electricity, known as alpha spots. At this point we need all the surface area we can get. So the contractor then takes away surface area. You can see this property in action in a variety of ways such as noticing that "cable failures" are almost never in the middle of the cable. They always start at the joints, even if it's a cable failure and not a joint failure.
3. The cable lug is designed for a specific amount of material to be present and actually crushes and essentially cold welds the materials together in order to achieve "intimate contact" and hence...alpha spots. Taking away material compromises this. Take away enough and you'll get a high resistance joint instead. Typically though this is an extreme problem.
4. What about the loose strands that remain? These will create electromagnetic fields (arcing, tracking, and other corona phenomena) which creates electrical noise as well as other problems if it is severe enough such as overheating at the joint, although this is mostly a bigger problem at medium voltage.
5. The mechanical properties are compromised. So under fault conditions the joint can fly apart.

Simply put, "trimming the hair" should be tantamount to trimming the work force.

PaulEngr just to clear this up In no way was I condoning this practice it was just sarcastic reference to wbd’s comment above about the practice of the "haircut", hence why I expanded on options to terminate aluminum conductors [procuring the proper lug kit, pin terminals, etc.] the image below is reference to the EC&M article from the April issue.

I thought so but sarcasm doesn't come across in print form very well, so sometimes it's hard to tell. I can honestly say that most of the flagrant hair trimmers don't even realize the problems they cause, even if they go back to the exact same spot and repair the same cable all over again, and trim it in exactly the same way.

And personally there is nothing more aggravating when it comes to terminations than stuffing welding cable or DLO down into a crimp on lug and crimping it down only to find that one little strand didn't make it into the lug and having used up the last lug in the box.

In the last 5 years or so I have seen a large uptick in the number of projects using AL for their larger conductors. Typically there is a minimum size below which all wiring is Cu, and above that every thing is Al. In my most recent, it is everything large, except motor circuit conductors, which are CU.