"The wire is called "Type R" or "rubber covered building wire". I have hundreds of feet of the single conductor type to do the openwork wiring in my museum trailer. openwork is like K & T, but with the wires on the surface, and on 2 wire cleats, with knobs used at corner bends to keep spacing 2.5 inches--if you put a cleat at an angle for a 90 degree turn the wires from the last cleat and first after the one on the corner will be at less than 2.5" apart and this is a no no. Using single knobs at the corner allows spacing to be maintained. They will raise the wire up a little because they are 1 inch tall, that is they hold the wire 1 inch from the surface wired over, wile cleats ate 1/2 inch and hold the wires a half inch above the circuits wired over, for that reason, cleats are NOT allowed inside walls, etc, in other words, for "concealed Knob and tube wiring" which MUSE be 1 inch minimum above the surface wired over. Wherever wires come closer together than 2.5" for openwork wiring or 3" for concealed wiring, and also enter switch boxes, or pass through the walls and ceilings to be spliced in the canopies of fixtures (yup no box!), they must be encases either in "circular loom" which is a special fabric tubing that adds extra insulation to the wire, or in tubes daisy chained on the wires to the termination point. Wires of opposite polarity or from different circuits, or switch loops etc, where they cross must have either loom or a tube on one of the 2 crossing wires to isolate them. Unless boxes (wall cases) have knockouts and internal built in clamps made especially to accommodate circular loom, the boxes MUST have porcelain bushings with center openings large enough to allow the loom to pass into the box, unless in open wiring where the hole only needs to be large enough to take the wire itself, and the loom can be run up against the bushing. the loom must be continuous from the last knob or cleat to the box, bushing, or terminal of cleat sockets and rosettes. Rosettes made to be installed in cleat work that have open or covered "pass through" terminals that maintain spacing of 2.5" and 1/2" above the surface can be installed between said conductors without any loom or tubes installed, and only enough insulation need be removed from the rubber wires to fit under the terminal screw--passing straight through and NOT looped around. This allows installation of more rosettes on existing openwork wiring, or relocating them elsewhere, all that is needed it to tape up the bare spots with rubber followed by friction tape at the former location of the rosette. Such c;eats may also be considered as regular support points like a regular cleat when installed as above. If a clear rosette or receptacle (bulb socket) is removed and is a regular spacing support, after taping up the bared spots, a regular 2 wire cleat MUST be installed just aside of the taped over spots, to provide continued support of the wires at that point. Where wires cross under or over pipes , etc, they MUST be in circular loom or tubes. If said pipe is liable to sweat and drip in summer, or leak, it is better to cross the pipe OVER than under, and to be sure the loom does not contact the pipe, as if it gets wet it's insulating properties are vastly reduced, and it can rot. At the end of a run, where a cleat is within the required 6" to 8" of the last rosette or cleat receptacle, the wires between the last cleat and the rosette or receptacle MUST be in circular loom or tubes despite the terminals maintaining proper spacing and clearance, for extra safety at the end of a run. (and good workmanship and appearance) Where rosettes are unavailable, a standard split knob will serve as a rosette, as will a "cord button" which is normally used to offset a lamp drop cord from the current rosette location to one to one side or in any direction aside of the main rosette, and can be placed between the 2 wires of the openwork run, and after securing the cord in the case of a cord button by tying the "underwriter's knot" in the wires of the cord, or in case of a split knob bu merely placing each wire in a separate groove of the knob and tightening the wood screw up, firmly clamping the cord's wires in place, keeping them separate as well.Small pieces of loom may be placed over the cord wires before tapping by soldering and taping, into the main openwork run, but as long as the cord wires are kept apart loom here is not essential but is good workmanship, and such a rosette is substantial and safe." I can go on all night because I LOVE this type of wiring, and working with it is pure "zen".
The cable shown here is old Non-Metallic Sheathed cable, known by it's trade name as "Romex cable", and I have seen some with type R cloth braided wire, and also some slightly newer stuff with PAPER braided wires! YUP PAPER braid over the rubber! I also have seen some rare stuff with the overall outer cloth braid, and no braids on the wires, just neoprene insulation with painted on or dyed in colors. I have some armored cable, trade name "BX" with this rubber only insulation, and the rubber was VERY high quality, because I have yet to see this stuff with cracked or brittle insulation, even though it is rare. seems most of this stuff was made immediate post war (WW2) when materials were still in shirt supply, and most of this rubber only stuff was made by GE. The compound is called GE-O-Prene. I have some I actually installed in my shop out back, just because I had some and wanted to use it, and it is fine. In many cases this type can be used in place of ACL cable which has lead-sheathed type R wires inside for outdoor and wet location use, like feeding signs outdoors--as the neoprene is totally waterproof, won't rot like cloth braids do, and is MUCH lighter to handle than ACL. Today you'd just use liquitite flex or even type MC cable with aluminum armor, and THHN wires inside with the separate green ground. "Modern" vinyl insulated wire was originally type T, for thermoplastic insulated (plasticized vinyl) The type TW came out--type T, but water resistant, with a better plasticizer that won't migrate out and leave the insulation dry and stiff in water. Then type THW came along, this is also called "machine tool wire" and is often finely stranded for high flexibility, hence machine tool wire. Some is moderately flexible 7-strand, some is single strand solid wire. The THW means Thermoplastic, heat and water resistant. The old T and TW was rated at 60 degrees centigrade max running temperature. The THW is rated at 75 degrees C. Please note that when wet, these are all 60 C. max, as water lowers heat resistance. Then, the "modern" (it is not--it started coming around in the mid 1960's) wore is THHN/THWN. Thermoplastic insulated, the 2 T's mean a maximum operating temperature of 90 degrees Celsius, about 158 fahrenheit. In the THWN part of the type, both of which are usually used on this type of wire, you can see the heat rating is derated back to 75 C. like THW, and the W is water resistance. The N means Nylon over covering, a modern "braid" so to speak. This nylon is what makes THHN/THWN so shiny. So, like the old type R, it is insulation with an outer "braid" so to speak. Type R is rated at 60 C. It can be used in damp locations but should never be allowed to get wet, as the fabric braid will rot off. Type RW is like TW, but rubber (neoprene) insulated, with a fiberglass outer braid, so water resistant, and still 60 C temp rated. The unbraided stuff mentioned above is also type RW, but called RWU--because it is unbraided, hence the U. Type RHW can be 2 types of insulation actually. The older version is like RW--neoperne rubber with a fiberglass braid, and rated higher at 75 C (60 C. wet.) and a second type, mainly made by GE under the "Vulkene" branding, which is actually type RHW/XHW. It is NOT rubber covered, but cross-link ployethylene covered, and was marked RHW because it was the new replacement for this wire. XHW is what it really is, X for cross-linked polyethylene, H for 75 C. heat rating dry, 60 C wet, and W for water resistant. HXXW is the 90 C version of XHW, and in fact, most HXXW is actually good for up to 150-170 C dry, hence why you see it alot on HID fixtures to wire the units, especially GE stuff. They use the fixture wire equivalent, which is XXF or XXXF fixture wire. One last wire type I have on hand and also encounter alot is used alot in fluorescent fixture from years ago, even on older ballasts and on incandescent socket lead wires, which is made in up to #12 size--type AF, or type AFB. This is asbestos insulated, and type AF is good for up to 150-180 C, was also used alot in stoves and heating appliances, and uses a special wax to make it soft. This wax dries out and it often gets stiff and brittle. It is safe to handle unless badly falling apart, and even then wetting it with a solution of soapy water will allow safe handling if it scares you (it does NOT scare me) Type AFB, often seen ol early GE ballasts, and on chain hing high wattage incandescent fixtures up the chain, is type AF with an outer decorative and protective braid, which is usually silk, or rayon, and in some cases heavier and more durable but not as good looking mercerized cotton like type R uses. when in good shape these wires have a soft, pliable feel not too unlike firm leather lacing. Hope you all enjoy this posting! Rick "C-6" Delair. BTW--type T wire is really hard to find, I have a little in my collection, but type TW and the newer types mentioned are common as are all the rubber types except the cables with the unbraided type RW. Also, some of the type RW and RHW, especially in BX cables had a simple spiral wrapped braid, that tended to unravel and look all frayed and crappy. it is no issue as long as the rubber is good, and usually is unless exposed to alot of heat, and once you know what color is what you can use colored phase tape or paint the rubber, and just leave the unraveled braid in the box. These fiberglass braids can stick fibers into your skin and can hurt and itch, so wear light gloves if it bothers you. Otherwise it is good stuff!