I have seen circuit breakers being employed as on-off switches to control electrical equipment. Just recently I was in a room that had a single-pole circuit breaker on the wall to control a window type air-conditioner. The breaker was just a couple of feet below the air-conditioner. The air-conditioner circuit should be originating from a circuit breaker in a distribution panel, otherwise the electrical code was violated. If the circuit did originate from a circuit breaker in a distribution panel somewhere in the building, then why was a second circuit breaker used as a switch? A regular switch, properly rated, could have been used as on-off control for the air-conditioner.
There are also cases where equipment is being turned on and off using the circuit breaker where the circuit originates. In other words, someone goes to the distribution panel and switches the breaker every time the equipment is to be turned on or off. The question now is: should circuit breakers be used as switches?
The National Electrical Code (NEC) - [2008 Edition], defines a circuit breaker as “a device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating”.
By stating that a circuit breaker is designed to open and close a circuit by nonautomatic (manual) means, the definition above is indicating that a circuit breaker can be used as a switch. This is so but, generally, circuit breakers are not designed as replacements for switches, or for contactors and motor starters. They are not intended for frequent, repetitive, manual on-off type control of electrical equipment. The main purpose of a circuit breaker is to protect a circuit from overload and short-circuit currents. The continual turning off and on of a breaker could weaken or damage the internal mechanism and reduces its protection capability. In most cases, circuit breakers are only expected to be manually operated to facilitate maintenance and repair type activities.
There are some circuit breakers, however, that are designed for routine on-off control of fluorescent lamps. These breakers are marked “SWD”, for switch duty. A circuit breaker with a switch duty rating does not mean that it should be used for manual high-frequency, switching-control operations. They are usually used in places where the lights are turned on in the morning and shut off at nights, such as in large warehouses.
So, yes, a circuit breaker is a switch but it should not be used as an on-off control switch for electrical equipment unless specifically designed for that purpose. A regular switch should be used instead. A regular switch is designed for high duty cycles, and it is usually cheaper than a circuit breaker of a similar load rating, since the circuit breaker has to be used with an appropriate panel.