A contact breaker is an electrical device generally used in the ignition system of an internal combustion engine. Contact breakers are sometimes referred to as "points" and are typically used to temporarily interrupt the electrical current passing through an ignition coil. This device is often utilized in combination with an electrical capacitor and is usually located in the distributor component of an engine. Contact breakers generally require frequent readjustments to perform properly, and their use has declined in recent years. Most modern internal combustion engines utilize an electronic ignition system that does not contain a contact breaker.
Older internal combustion engines typically have an ignition system consisting of a battery, distributor, ignition coil, and spark plugs. The ignition coil consists of a shared magnetic core surrounded by two sets of copper transformer windings. The primary set of windings creates a magnetic field in the shared core. The secondary windings create a step-up transformer which produces the high voltage electrical current needed for the spark plugs to ignite the engine’s fuel. A contact breaker is used both to conduct and interrupt the flow of electricity to the ignition coil.
During the ignition procedure, electrical current from the battery passes through the contact breaker en route to the ignition coil, distributor, and spark plugs. Inside the distributor is a rotating cam that opens and closes the contact breaker. When the breaker is closed, a short burst of electricity is sent to the ignition coil. When the breaker is opened, the electrical current is suddenly stopped, and a large amount of electricity is built up in the secondary winding of the ignition coil and sent to the spark plug. This process is repeated sequentially for each combustion cylinder of the engine.
A small gap between the contact points of the breaker allows an electrical arc to occur when it is in the closed position. This arc can cause the breaker’s contact points to become damaged over a short period of time. To reduce the damage to the breaker, an electrical capacitor is often used as one of the breaker’s contact points to suppress the arcing and increase the output of the ignition coil. Contact breakers have a tendency to become misaligned during use and often require readjustment between regular service intervals.
The use of contact breakers in ignition systems has been greatly reduced in recent years. Electronic ignition systems utilizing magnetic or optical sensing devices are now commonplace in most engines. These sensing devices have proven to be more precise and offer better high speed engine operation. Contact breaker ignition systems continue to be used in aircraft engines, however, because they are not as prone to sudden catastrophic failures as electronic sensors.