Relays, Timers & Counters
Different types of relays, such as electromagnetic relays, solid state relays, and time delay relays, have specialized components or functions for specific applications.
Click here for more about what a relay is and how it works.
Click here for things you must know about relays.
Click here for more about the differences between relays and contactors.
Click here for more about the differences between single-throw and double-throw relays.
Click here for instructions on how to wire a relay.
Click here for more about the differences between electromechanical and solid state relays.
FAQ
What are poles in a relay?
Poles refer to the number of isolated, energizing circuits that can pass through the switch. A single-pole contact (SP) can carry current though one energizing circuit at a time, while a double-pole contact (DP) can simultaneously carry current through two energizing circuits. Three-pole contacts (3P) and four-pole contacts (4P) are also common, but relays with up to 12 poles are possible.
What are throws in a relay?
Throws refer to the number of closed contact positions that are available per pole on a switch. A single-throw contact (ST) controls one contact circuit, while a double-throw contact (DT) controls two. Throws that are normally open (NO) are open by default. This means that until a current passes through the pole (the energizing circuit) the throw (the contact circuit) is not closed and no current is passing through it. When the contact circuit is closed the current passes through the now completed circuit. Throws that are normally closed (NC) are closed by default. This means that a until a current passes through the pole (the energizing circuit) the throw (the contact circuit) is closed and the current is passing through it. When the contact circuit is open the current no longer passes through the incomplete circuit.