NEC in the Facility, Nov. 22, 2011

Commonly misunderstood/misapplied terms, part 11

Commonly misunderstood/misapplied terms, part 11.

Article 100 defines six kinds of switches, but it doesn't define the word "switch." Several major dictionaries define a switch as a device that opens or closes a circuit, or changes the connections from one circuit to another. That makes a circuit breaker a special kind of switch.

Here's a list of six different types of switches:

  1. General use. It's for distribution and branch circuits, except where you need a special switch.
  2. General use snap. The "snap" part means you can install it in device boxes or covers.
  3. Motor circuit. It's rated in horsepower; you use it with a motor of the same rating.
  4. Isolating. It isolates a circuit from the power source but not by interrupting the power. It has no interrupt rating. You first open the circuit (via breakers, for example) and then open the isolating switch. Lock it out, and the circuit can't be accidentally energized.
  5. Transfer. It "moves" the load conductors from one supply to another supply. It may be automatic or manual. If you have sources A and B, the switch allows you to connect to B and disconnect from A, or vice-versa.
  6. Bypass isolation. Manually operated, it allows you to cut the transfer switch out of the circuit and connect the load to the source.
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