The overloading of an electrical circuit is dangerous and can cause a fire.
One mechanism in the prior art for preventing an electrical circuit from overloading is a “fuse.” A fuse is a conductor that is placed in series with the electrical circuit that it protects. When the current through the fuse exceeds a threshold, the fuse heats up, burns, and opens the circuit. This protects the circuit and prevents a fire. A fuse is disadvantageous, however, in that it cannot be reused.
A second mechanism in the prior art for preventing an electrical circuit from overloading is a “circuit breaker.” A circuit breaker is an electro-mechanical apparatus that is placed in series with the electrical circuit that it protects. When the current through the circuit breaker exceeds a threshold, a switch in the circuit breaker is opened. The opening of the switch opens the circuit, stops current from flowing, and prevents a fire. The circuit breaker is advantageous because the switch can be closed and the circuit breaker can be reused.
FIG. 1 depicts a schematic diagram of the salient components of circuit breaker 100 in accordance with the prior art. Circuit breaker 100 comprises: terminal 101, terminal 102, first switch 103, electromagnet 104, and second switch 105, interconnected in series.
First switch 103 is a single-pole, single-throw relay switch that is opened by electromagnet 104 when the current I flowing through electromagnet 104 exceeds a threshold current IT (i.e., I>IT). When the threshold current through electromagnet 104 exceeds the threshold current, electromagnet 104 opens first switch 103, which prevents all current from flowing through circuit breaker 100. This protects the circuit and prevents a fire.
Second switch 105 is a single-pole, single-throw thermally-activated switch (e.g., a bi-metallic strip, etc.) that bends and opens when the current I flowing through electromagnet 104 exceeds the threshold current IT. When the current through second switch 105 exceeds the threshold current, second switch 104 opens, which prevents all current from flowing through circuit breaker 100. This protects the circuit and prevents a fire.
First switch 103 and electromagnet 104 are designed to protect the circuit from sudden increases in current (i.e., current “spikes”), which might be caused, for example, when an electrical appliance is dropped into water. In contrast, second switch 105 is designed to protect the circuit from slowly-changing, but also dangerous increases in current, which might be caused, for example, when an electrical appliance awakes from sleep mode (i.e., an electric heater controlled by a thermostat).
Switch 103 and 105 can be combined into a single switch that can be acted on by an electromagnet, and can also be activated thermally.
One advantage of a circuit breaker over a fuse is that the circuit breaker can be re-used after it trips and is reset. One disadvantage of a circuit breaker over a fuse is that the circuit breaker is more expensive.