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Type of electrical circuitry Knob-and-tube circuitry in a 1930 home. View looking upwards at upper wall stud bays and close-by ceiling joists Knob-and-tube electrical wiring used in a commercial textile factory.
Where conductors went into a wiring gadget such as a light or switch, or were pulled into a wall, they were protected by versatile cloth insulating sleeving called loom. The first insulation was asphalt-saturated cotton cloth, then rubber ended up being common. Wire entwines in such setups were twisted together for great mechanical strength, then soldered and wrapped with rubber insulating tape and friction tape (asphalt saturated cloth), or made inside metal junction boxes.
, such as specific commercial and farming environments. Most had a circular groove running around their circumference, although some were constructed in 2 pieces with pass-through grooves on each side of the nail in the middle.
By wrapping electrical wires around the knob, and securing them with tie wires, the knob might be used to securely and permanently anchor the wire. The knobs separated the wire from potentially combustible framework, helped with modifications in instructions, and ensured that wires were not subject to excessive tension. Due to the fact that the wires were suspended in air, they could dissipate heat well (knob and tube removal in Ottawa).
This kept the wires from coming into contact with the wood framing members and from being compressed by the wood as your house settled. Ceramic tubes were sometimes also used when wires crossed over each other, for security in case the upper wire were to break and fall on the lower conductor.
Not all knob and tube setups used cleats. Ceramic bushings secured each wire going into a metal device box, when such an enclosure was utilized. Loom, a woven versatile insulating sleeve, was slipped over insulated wire to provide additional security whenever a wire passed over or under another wire, when a wire got in a metal gadget enclosure, and in other circumstances prescribed by code.
Circuitry gadgets such as light switches, receptacle outlets, and lamp sockets were either surface-mounted, suspended, or flush-mounted within walls and ceilings. Just in the last case were metal boxes always utilized to enclose the electrical wiring and device.
Knobs supporting long runs of wire Knobs serving multiple functions Ceramic tubes protecting wires passing through ceiling joists. Circuitry running through tubes, and turning a corner supported by a knob.
, and a junction box should have been utilized. In many older K&T installations, the supply and return wires were routed independently from each other, rather than being located parallel to and near each other. This direct routing method has the advantage of lowered expense by allowing use of the shortest possible lengths of wire, but the major downside is that a detailed building circuitry diagram is required for other electrical contractors to comprehend several interwoven circuits, especially if the wiring is not completely noticeable throughout its length.
Electricians must be mindful of this older system, which is still present in many existing older electrical installations. (return) wire of an electrical circuit.
Because of the presence of a neutral fuse, and on the occasion that it blew, the neutral conductor could not be counted on to remain near ground capacity; and, in truth, might be at full line potential (through transmission of voltage through a switched-on light bulb, for example). Modern electrical codes generally do not require a neutral fuse.
In the early 1900s, K&T wiring was less pricey to set up than other circuitry techniques. For numerous years, electricians might choose in between K&T electrical wiring, avenue, armored cable, and metal junction boxes. In 1909, versatile armored cable expense about twice as much as K&T, and channel cost about 3 times the cost of K&T.
Modern circuitry approaches assume two or more load-carrying conductors will lie very near each other, as for circumstances in basic NM-2 cable. When installed properly, the K&T wires are held far from the structural products by ceramic insulators. K&T wiring was typically insulated with cotton cloth and soft rubber, in addition to the porcelain standoffs.
Today, porcelain standoffs are still commonly used with bare-wire electric fencing for livestock, and such porcelain standoffs carry far greater voltage rises without risk of shorting to ground. In short, K&T wiring that was set up properly, and not damaged or incorrectly modified since then, is fairly safe when used within the initial current-carrying limitations, about ten amps per circuit.
Compared to modern electrical wiring requirements, these are the primary technical drawbacks of knob-and-tube electrical wiring techniques: never consisted of a safety grounding conductor did not restrict changing to the hot conductor (the so-called places electrical loads across the typical terminals of a three-way switch pair) permitted using in-line splices in walls without a junction box (however, this disadvantage is offset by the strong nature of the soldered and taped junctions used at the time).
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