PSA: Not all cloth wire is knob and tube!
All too often a homeowner posts wire coming out of a junction box like the first picture and a lot of people tell them “Knob and Tube, you must replace it”.
I’m here to tell you that houses exist (outside of Chicagoland) that run this wire safely in conduit.
I recently posted asking about the job I just finished. My house, built in 1920 in Western NY is built largely with rigid conduit, California Three-Way Switches, and all electrical going to the ceiling box in each room before dropping to outlets and switches. In all of the original conduit in the house, the wire is the cloth wire in the first picture.
The conduit (rigid or flexible) carries the ground, meaning that by simply installing a grounding clip or grounding screw, I have been able to update the few remaining two-prong outlets and get a true ground on test. With rigid conduit, this ground is also code compliant per NFPA 70/NEC standards. I think Flexible conduit used to be allowed to carry a ground but it has since been limited to only carrying a ground for 6 feet or less (more on this below).
This cloth wire is also 14 gauge copper wire, the same stuff used today and found in ROMEX. I’ve been doing my own electrical work since 2012 (haven’t burned down the house yet) and only in rare occasions do I find the copper brittle, and even then cutting about 1/2” and inch is all it takes to get a nice flexible end to twist. The insulation is protected by the conduit and there is no just reason to replace cloth insulated wire.
The only real problem with my cloth wiring is that if they were originally different colors they are not anymore, so I do run a higher risk of switched neutrals (as I had to the original switch on this job) and I have to confirm the hot wire (hence the red and white electrical tape). But this problem is not a show stopper and it helps to keep me aware of what I am doing.
So what did I do on my job? I’d wanted to install a new outlet in my bathroom for a future fancy toilet and provide GFCI to the fan above my shower that does not currently have protection and is considered unsafe in that case. I knew from messing with the switch that this is an original outlet (my house does have a few newer, Romex-fed circuits). I assumed that I would be dealing with rigid conduit - lo and behold when I take out the wall I see flex conduit. This threw me for a loop, but then I realized that the conduit is perfectly fine and this actually ended up much cheaper to install.
Cutting the conduit at this diameter (1”) was not fun. I eventually used my multitool and managed to be careful enough to avoid cutting the wires. I had made a deliberate choice to keep this circuit all metal (as I thought the ground was through the conduit) so installed a coupling and installed a metal handy box. Now, although per code, the flexible conduit does not carry the ground, I knew for practical purposes it did, and besides I was installing a GFCI anyway. So I put a ground screw in the box and connected a ground to the outlet. It turned out later when I tested this, it did have a true ground, not just an equipment ground, so this 1920 flex conduit is still in good shape.
From the new GFCI, I decided to use the original flex conduit but install new wire so I can have a ground wire. I cut the cloth-insulated wire above the GFCI (this is what the first photo shows), and I pulled new NM (Romex) (just kidding, NM isn’t allowed in conduit by code due to heat issues) three wire through the conduit. I would’ve used NM, but I only had 14/3 which I didn’t want to waste the extra conductor but I happened to have a spool of 14ga black/white/green cable from wire in conduit replacement work I did elsewhere to get a neutral to a wall switch. i connected up a light switch and humidity fan switch and my bathroom fan is now GFCI protected.
I’m not a professional. It took about 8 hours including drywall repair and I likely have another hour or two of sanding and painting tomorrow, but at the same time, I likely saved $500+ for a professional.
The coolest thing of all is that all of the parts in my 1920 home were built to the same material standards as today. I was able to buy the same coupling (just Phillips instead of slotted screwed) for the conduit and it goes on easy.
So in the future, when a homeowner posts a pic of cloth wire, stop telling them it is knob and tube. Ask them to check and see if the wire is in conduit. If so, the house is either up to code or a lot closer to code than something built with first generation NM without proper grounding.