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There are many different wiring diagrams for switched circuits, including three-way and four-way switching, and these diagrams have guided electricians and others for decades. They’ve also remained largely unchanged for decades. But with many switch and device arrangements, complicated with jargon such as “travelers” and “switch legs,” these installations have been known to go sour after the fixtures and switch trim are installed; for example, when a three-way switch won’t respond to the second switch being tripped. With the 2011 National Electric Code, these ubiquitous but often misunderstood wiring arrangements were tweaked, and in 2014 they were revised, rendering many of the old diagrams obsolete—particularly when a switch is placed at the end of a circuit.
So why the changes? Codes are regularly updated to stay in step with society’s changing expectations of safety, affordability, and convenience. Codes also adapt to changes in technology.