Contactors and relays are switches that allow control of a system by opening and closing under power. There are two major components that make up these devices: a coil and contacts. When a small current is applied to the coil, it creates a magnetic field that pulls a contact into the opposite position. The contacts come as either normally open (NO) or normally closed (NC) and they allow different control states within a circuit. A normally open contact on a relay doesn’t allow current to flow in its natural, unactuated state; when power is applied to the coil, it then allows current to flow. A normally closed contact functions in the opposite way - it allows current to flow in its natural, unactuated state, and stops the flow of current when actuated. Contactors and relays can be purchased with many different configurations of contacts.
The contacts on relays are rated for lower currents, usually from 0.25-12 Amps. Contactors, however, are usually rated for a much wider range from 0.25 Amps (voltage dependent) up to many hundreds of Amps. Contactors are usually more rugged than relays but have cost and size drawbacks and can potentially be overkill for smaller applications.
In addition to standard relays and contactors, safety rated relays are used to reduce the risk of damage to a system in the event of a failure or hazard. In a typical application, emergency stop pushbuttons and other safety devices are wired directly into a safety relay. This allows an operator to instantly cut control power for a system in the event of an emergency, preventing the system from energizing any outputs and keeping operators safe.
We at Premier Automation have the expertise to design, service, and upgrade existing relay-controlled systems to meet your needs. Whether you need a new control system or a refurbishment of an existing application, our automation experts are available to help!