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This article describes the electrical wiring color code conventions for 120V or 240V AC circuit wiring in buildings in Canada, the U.S., the U.K. and the I.E.C. Quoting from authoritative codes & standards for each region we provide a table summarizing the current and prior wiring color code conventions used by electricians in building wiring. For each color code table we include authority citations and links to sources of codes, books, standards and wiring guidelines. We point out with photo-examples that while wire color code theory is nice and all that, in the real world of working on existing buildings, wires are not always reliably color-coded and colors may in fact be impossible to discern. Some of the wire color images here were adapted from data provided by the Malta Resources Authority's excellent document on Harmonisation of Wiring Colour Codes - cited below.
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But as we illustrate below, on some older buildings spotting any color at all in the wiring insulation or jacket can be difficult or even impossible.
On older wiring such as this rubber and fabric-jacketed household wiring from a U.S. home, figuring out what the heck the wire colors are can itself be a challenge.
Look closely at the fabric covering of the two wiring strands in our photo.
The upper wire is the "white" or neutral wire.
The lower wire, whose fabric insulation is black with red and white tracer threads is the "black" or hot wire.
But sometimes there is no clear color distinction between the two wires: you'll need to trace the wiring and use a DMM or VOM to figure out which wire is "hot" and which is neutral or ground.
First we can see that if we're in luck, the fabric portion of the wiring insulation may be intact and may clearly show that one conductor is white (neutral) and the other black (hot). With age the white insulation may have become tan or even brownish in color.
Second I'm a bit nervous about how that white wire is stripped back and is in contact with the hot black wire (arrow).
Finally, of course there is no protective ground on this circuit - we've got just two wires with which to contend.
This wiring shown above - well don't even think about figuring this out by color codes. Someone has just grabbed a piece of yellow wire and a blue wire, left an open splice, and jury-rigged something (not shown in our photo).
But when you see obviously amateur electrical--wiring like this it's a red flag to watch out, asking "what else did this fellow wire in this building?"
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