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I had an electrician come out to my 1920s Chicago Bungalow, and he told me that all the original electric was "piped," that is, sheathed in rigid steel raceway, with the piping serving as the ground back to the breaker.

The original cables themselves (in the circuits that have not been upgraded) are rubber and cloth.

Everything I've read up until this point says that most houses from this period were built with either knob and tube or in some cases flexible/BX conduit. Can anyone corroborate that circuits were "piped" in this era? Or was he possibly talking about BX and I just misunderstood?

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    Quite possible the circuits have been upgraded/redone since the 1920s, maybe after code changed to require conduit. Rigid steel raceway should be quite smooth, where BX will be bumpy. Should be easy just by looking.
    – crip659
    Jan 2 at 17:32
  • Pictures would help. Jan 2 at 17:57
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    @manassehkatz-Moving2Codidact Now that the fixture is in I'd rather not take it down just for a picture of the pancake box, but it sounds, from some of the comments below, this is actually fairly standard in old Chicago homes.
    – Chris S.
    Jan 2 at 18:36
  • In the old days, some houses were equipped with gas lamps in every room. The gas lines (iron tubes) were repurposed for electric wiring when that new fangled electricity showed up. Jan 3 at 1:51

2 Answers 2

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My house in western NY state was built in the the 1920's, and the original wiring is in rigid conduit that is painted black.

Of course there have been numerous additions over the years, so I can find BX, early cloth-covered NM, and more modern NM-B, but the original is definitely rigid conduit.

I've been slowly replacing the original cloth-covered wires with THHN/THWN, but I've also been adding a ground wire too. That old painted steel conduit is rusting, so you have a rusty steel conduit attached to a rusty painted steel junction box, and then another rusty conduit connected to that rusty junction box, and so on. And on top of that some of those conduit connections are loose too. I don't trust that chain of rusty steel connections in the conduit to provide a good ground path all the way out to the end of a chain of connections, so that's why I've been adding the ground wires. The grounds get connected to each device in the junction box, but I also drill and tap a 10-32 hole in each junction box for a ground screw and connect a pigtail.

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It's Chicago. See Mrs. O'Leary's Cow (1871, currently held to be wrongly blamed) for why the wiring is done in conduit in 1920.

There is absolutely nothing wrong (and a great many things right) with wiring in Rigid Metallic Conduit (RMC), and when the wire insulation finally degrades far enough to be an issue, the wires can be pulled out and replaced with "modern" ones (that's just one of the "right" things.)

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  • I was relieved to hear it, since it's much safer than what I assumed was there (knob and tube). I was going to have cable for the the whole circuit replaced, but since the old cable seems to be in pretty good condition at the box, that's a lower priority now.
    – Chris S.
    Jan 2 at 18:38

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