Why is there so much metal-clad wiring in my house?

Question

My house was built in 1893. I was recently doing some electrical work in the attic, adding some light fixtures. While doing that, I noticed that several of the upstairs outlets were wired with old, worn-looking metal clad wiring. Since I wanted to replace the outlets anyway for style reasons, I replaced this old wiring with new 14/2 NM w/G (Romex) wiring. I also used the same romex for the new lights and switches (fished into interior wall cavities).

In further exploration, I've found this house has a lot of metal-clad wiring. Not only in places where you might want some extra protection, like a long run alongside the chimney or in a crawlspace, but also in places that seem totally straightforward and safe, like first-floor outlets and light switches. And it seems relatively recent (within the last 30 years).

Is there something I'm missing that might require metal-clad wiring in this house?

Bonus question: what's a good way to recycle lots of old metal clad cabling? :)

Answer 1

The flexible armored wire you are seeing is often referred to as AC or BX cable. (BX was a brand name like Romex is for NM) Bx was used extensively prior to 1960ish and is still used today. There are no current code requirements that require this kind of cable in residential construction and it has almost all but been replaced with NM. As you have probably already figured out, BX uses different box connectors, and many of the device boxes you have in place were probably made to terminate BX cable.

Although it is perfectly legal to use, and actually quite safe, it is rarely used because of it's higher cost and relative difficulty to install and terminate. The only caution I would emphasize is the ground conductor in older BX. it was very common not to use a separate ground conductor when using BX, and often when there was a separate ground wire, it was a smaller AWG that the black/white/red current carrying conductors. this was never a problem if the BX armor was properly attached to the metal junction boxes and again properly connected at the panel, thus making a substantial grounding path.

As far as the bonus question. BX is heavy and probably brings a good price at the metal recycling brokers. A couple of years ago when junk metal was really hot, a good load would have been worth hundreds of dollars. It was a popular find for junk dealers and the target of theft.

Answer 2

While there may well be "no codes requiring it in residential", as is often pointed out, exceeding codes is OK.

Is "modern" romex better - not if you ever have mice. If the wiring is not deteriorating, there's no good reason to replace it, and plenty of good reasons to leave it alone.

Why so much - it was probably what was common when the house was wired or re-wired. If it's really less than 30 years old, (may just be in better shape than you expect for its age) perhaps the house was rewired by someone who had had a house fire from mice chewing on plastic insulated wires. Most 1893 houses won't have modern fireblocking, and can't really afford a fire in the walls...

Answer 3

For the bonus question, I just remembered something someone told me not that long ago. He said a recycle company told him the scrap value of steel sheathed AC is based on the current value of steel. If that's true for most or all of them, it wouldn't be worth much unless you removed the copper and recycled it separately.

Answer 4

I am an inspector for a municipality in Cook County. I have a Chicago electrical license which is the gold standard around here since there is no state license to be had. I've been an electrician for 20 years. At no time during those years has the City of Chicago ever allowed NM cable to be used. Recently, Chicago adopted the 2017 NEC and then amended it to suit their needs. They amended out the requirement for Arc Fault protection as long as the electrical system is all metal piping or MC cable w/ metal boxes. In my municipality we also do not allow NM/Romex. I agree w/ Eric above on both of his stated reasons for this but mainly it's to keep clueless people from doing electrical work. You'd have to drive an hour or more from Chicago to find a place that allows the installation of NM cable.

Answer 5

If the wire you have discovered was smooth and not knobby (wound) then it is likely what was called flex or "Greenfield" (after the man the designed it) cable, widely used in the 1920-1940 era. The metal casing was actually used for grounding.

Answer 6

If you live in the Chicago area, "Romex" or nonmetallic cable has never been permitted. I'm not sure, but there might be other areas in the country that have the same requirement. As an electrician I wired my entire house in conduit and where I was fishing in existing walls, Flexible conduit(Greenfield).

For openers if you need to split up or add circuits at a later date you can fish additional wires through the conduit without having to open up walls. A second plus is the fact that rodents can't chew through metal conduit. Rodents DO in fact chew through wiring insulation that could either lead to circuit failure or fires.