circuit breaker

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An automatic switch that stops the flow of electric current in a suddenly overloaded or otherwise abnormally stressed electric circuit.
• noun An automatic halt or suspension in the trading on a stock exchange that takes effect in response to a specified amount of loss.

from The Century Dictionary.

• noun A device for opening or breaking an electrical circuit at regular intervals, usually a spur-wheel operated by clockwork; a rheotome.
• noun One of the best-known forms consists of a switch which is closed against the pull of a powerful spring. The lock by means of which it is kept closed is released by an electromagnet operated by the current.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Elec.) A device contained within an electrical circuit designed to interrupt the circuit when the current exceeds a preset value; it is sometimes called a contact breaker. Its function is to prevent fire or damage to the circuit or the devices on the circuit which could be caused by excess current, such as that caused by a short-circuit. It differs from a fuse in not having a conducting element which melts (see 2nd fuse, n.). Circuit breakers are designed to be easily reset, i. e. to reclose the circuit after it has been opened by the circuit breaker; this is usually accomplished by simply moving a switch back and forth. They are commonly used in buildings to protect individual electrical lines, and are often contained in groups within a box called a circuit breaker panel, which divides the current from a main electrical line into multiple circuits each protected by a separate circuit breaker. Less commonly they may be found on individual devices.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun electrical engineering An electrical switch capable of opening and closing an electrical circuit in all operating conditions, including fault situations.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a device that trips like a switch and opens the circuit when overloaded