A relay generally has five main terminals, though some models may have four depending on the type and design. In a standard Omron Relay, these terminals are divided into two parts — the coil terminals and the contact terminals — each performing a specific role in controlling electrical circuits.
The coil terminals are used to energize the relay. When voltage is applied across these two terminals, the magnetic coil inside the relay gets energized and causes the internal switch (contacts) to open or close. These terminals are typically connected to the control circuit, such as a PLC output or a switch.
The remaining terminals belong to the contact section, which controls the load side of the circuit. In a common relay with SPDT (Single Pole Double Throw) configuration, there are three contact terminals — Common (COM), Normally Open (NO), and Normally Closed (NC). The COM terminal is the central connection point that moves between the other two contacts. When the relay is in its normal (de-energized) state, the COM is connected to the NC terminal, allowing current to flow through that path. When the relay coil is energized, the COM switches to the NO terminal, completing a new circuit and allowing current to flow through a different path.
So, a typical Omron relay has five terminals — two for the coil and three for the switching contacts. Some simpler relays, such as SPST (Single Pole Single Throw) types, have only four terminals because they include just one switching contact (COM and NO).
In industrial automation, these relays are used for switching motors, heaters, and control devices. Omron relays are known for their reliability, long life, and precise switching performance, making them suitable for control panels, machinery, and protection circuits. The number of terminals and their configuration depend on the relay type, but the five-terminal design is the most commonly used in general-purpose applications.