The National Electrical Code defines a switching device as, "A device designed to close, open, or both, one or more electrical circuits." The devices that fall under this classifcation are circuit breakers, cutouts, disconnecting means, disconnecting (or isolating) switch (disconnector; isolator), interrupter switch, oil cutout (oil-filled cutout), oil switch, or a regulator bypass switch. Let's look at the definition of each of these in detail.
1. Circuit Breaker
The 2008 National Electrical Code book defines a circuit breaker as ,"A switching device capable of making, carrying, and interrupting currents under normal circuit conditions, and also of making, carrying for a specified time, and interrupting currents under specified abnormal circuit conditions, such as those of short circuit."
2. Cutout
The 2008 National Electrical Code book defines a cutout as, "An asembly of a fuse support with either a fuse holder, fuse carrier, or disconnecting blade. The fuseholder or fuse carrier may include a conducting element (fuse link) or may act as the disconnecting blade by the inclusion of a nonfusible member.
3. Disconnecting Means
The 2008 National Electrical Code book defines a disconnecting means as, "A device, group of devices, or other means whereby the conductors of a circuit can be disconnected from their source of supply."4. Disconnecting Switch
The 2008 National Electrical Code book defines a disconnecting switch as, "A mechanical switching device used for isolating a circuit or equipment from a source of power."5. Interrupter Switch
The 2008 National Electrical Code book defines an interrupter switch as, "A switch capable of making, carrying, and interrupting specified currents."6. Oil Cutout
The 2008 National Electrical Code book definesan oil cutout as, "A cutout in which all or part of the fuse support and its fuse link or disconnecting blade is mounted in oil with complete immersion of the contacts and the fusible portion of the conducting element (fuse link) so that arc interruption by severing of the fuse link or by opening of the contacts will occur under oil."7. Oil Switch
The 2008 National Electrical Code book defines an oil switch as, "A switch having contacts that operate under oil (or askarel or other suitable liquid)."8. Regulator Bypass Switch
The 2008 National Electrical Code book defines a regulator bypass switch as, "A specified device or combination of devices designed to bypass a regulator."
