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Special wiring rules apply to wet or corrosive locations, [13] and to locations which present an explosion hazard. [14] Wiring materials for use in the United States must generally be made and tested to product standards set by NEMA and Underwriters Laboratories (UL) and must bear approval marks such as those set by UL.
A 2.26 kΩ, 1%-precision resistor with 5 color bands (), from top, 2-2-6-1-1; the last two brown bands indicate the multiplier (×10) and the tolerance (1%).. An electronic color code or electronic colour code (see spelling differences) is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes and others.
The color combinations are applied to the insulation that covers each conductor. Typically, one color is a prominent background color of the insulation, and the other is a tracer, consisting of stripes, rings, or dots, applied over the background. The background color always matches the tracer color of its paired conductor, and vice versa.
However, it is a common misconception that "hot" conductor colour-coding is required by the Code. In the United States, colour-coding of three-phase system conductors follows a de facto standard, wherein black, red, and blue are used for three-phase 120/208-volt systems, and brown, orange or violet, and yellow are used in 277/480-volt systems.
A somewhat similar system called "concentric wiring" was introduced in the United States around 1905. In this system, an insulated electrical wire was wrapped with copper tape which was then soldered, forming the grounded (return) conductor of the wiring system. The bare metal sheath, at earth potential, was considered safe to touch.
Colour code [8] voltage range 20–25 V 40–50 V 100–130 V 200–250 V 300–480 V 500–1000 V common color violet white yellow blue red black common application 24 V single-phase AC/DC power single-phase AC/DC power 125 V single-/split-phase AC power 250 V single-/split-phase AC power 400 V 3-phase AC power 500 V on marine vessels
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NEMA 1-15P (two-pole, no ground) and NEMA 5-15P (two-pole with ground pin) plugs are used on common domestic electrical equipment, and NEMA 5-15R is the standard 15-ampere electric receptacle (outlet) found in the United States, and under relevant national standards, in Canada (CSA C22.2 No. 42 [1]), Mexico (NMX-J-163-ANCE) and Japan (JIS C 8303).