"Rag" wire was a loose nickname for cloth covered 2-conductor ungrounded wire manufactured mostly during World Wars I & II. Since most copper was diverted to war munitions during wartime, the wires produced during these times were made without Ground wires in them. The wires were cloth wrapped (and the 1920s version had additional cloth and/or paper wrapped around the internal conductors for safety. These wires are typically black, with the 1920s version being oversized due to all the extra paper and cloth inside it. The below photos are of some of my historical wire collection. 1920s "Rag" Wire - "unravelled" to expose the cloth/paper coverings:
Note that the tar paper thin inner wrap and the paraffin soaked spiral paper in this wire shown below were quite flammable - they were added to aid in making the wire more water tight - instead they made it more combustible!
We have encountered versions of this wire that: appeared to have an inner thin woven asbestos layer, had added aluminum ground wire, and had loose cloth wrapping on the wires instead of the paper wrap seen here.
The 1940s version looks much like black cloth covered romex - except it has no internal ground wire. (This can only be determined by checking the connections at panels and boxes - and looking for the ground wires at the wire's end - the ground wires when present were often undersized)
Below - Rag "Romex" from the 1940s (It was used in some areas up till the 50's) - Note the lack of ground wire inside the panel. (Be sure to look for the ground under the wire connector wrapped in a spiral around the wire - older systems often used this inferior and improper grounding method -- this wire had no ground at all)
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