What Is a Relay Board? Types and Selection Criteria
A relay board is a DIN rail board that isolates and boosts the low-current outputs of a PLC or controller through its relays, bringing several channels into one housing.
A relay board (relay module) is a DIN rail board that brings several relays together on one printed circuit and isolates and boosts the outputs of a PLC, controller or sensor through the contacts of these relays. Each channel is a relay: the control input drives the relay coil, and the contact output switches loads such as contactor coils, signal lamps or valves. It does the same job as individually socketed relays with less space and wiring.
Types
| Type | Construction | Model in the catalog |
|---|---|---|
| Open rail-mounted board | Board and relays are exposed; mounted on the rail with a carrier | Isıso ITRS8 |
| Enclosed rail-mounted board | Board inside a plastic housing; protected against touch and dust | Isıso ITRSK8 |
| Enclosed board with test | Enclosed housing plus a test feature for trying channels by hand | Isıso ITRSKT8 |
All three boards in the catalog have 8 channels and a 24 V DC supply.
Selection criteria
- Number of channels: Add spares to the number of outputs to be switched. The boards in the catalog have 8 channels; for more outputs, several boards are used.
- Coil voltage and input type: The board's supply and control voltage must match the output voltage of the driving device (24 V DC for those in the catalog). Check in the datasheet whether the PLC output is PNP or NPN and which common the board works with.
- Contact load: Take the contact current and voltage ratings from the datasheet. Switch motors, heaters and large coils through a contactor, not directly with the relay on the board.
- Housing: If there is a risk of touch or dust inside the panel, choose an enclosed type (ITRSK8, ITRSKT8).
- Testing and maintenance: If channels need to be tested independently of the PLC during commissioning and fault finding, the ITRSKT8 with test makes this easier.
Common mistakes
- Driving a 24 V board from an output at another voltage: The relay does not pull in or the coil is damaged.
- Switching inductive loads without suppression: The contact arcs and wears early; fit a suitable RC element or diode across the coil.
- Mixing up channel commons: If the common (COM) groups in the wiring diagram are not respected, loads at different voltages get connected together.
Relay boards at Welibaba
The Relay Boards category has 3 active products from Isıso, all listed with prices: ITRS8, ITRSK8 and ITRSKT8. Individually fitted slim coupling relays are in the Slim Relays category, and relay types are compared in the relay guide.
Frequently asked questions
What does a relay board do?
It isolates the low-current outputs of a PLC or controller with relays and lets them switch higher-current loads, bringing several relays into one housing.
Relay board or individual slim relays?
If there are many outputs in one place, a relay board reduces wiring and space. If channels are needed in different places or of different types, individually fitted slim relays give flexibility.
Can a relay board run a motor?
Not directly. The relay on the board drives a contactor coil, and the contactor switches the motor.