You can still browse the site but some services may not work properly. This site requires Google Chrome, Firefox, Safari or Internet Explorer 10 and above. For mobile devices use an HTML5 capable browser.Download Chrome
If you look up the definition of multiwire circuit in Article 100, you won’t find it under “Multiwire Branch Circuits.” You’ll find it under “Branch Circuits, Multiwire.” So, what is it?
A multiwire circuit consists of two or more ungrounded conductors (with a voltage between them) and a grounded conductor (e.g., neutral). The grounded conductor has an equal voltage between it and each ungrounded conductor, plus it’s connected to the neutral (or grounded conductor) of the system.
Basically, a multiwire is two circuits that share a common neutral. The NEC permits you to consider it to be two circuits [210.4(A)].
The advantage of this wiring scheme is you save some wire by not running a neutral. The downsides include:
If you weigh the tiny bit of installation cost-savings against the increased risk of loss of operations, these circuits are not justified for industrial and commercial applications.
Source: Mark Lamendola | Mindconnection