Industrial Relays Explained: Types, Applications & How to Choose the Right One
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What Is an Industrial Relay?
A relay is an electrically operated switch. When an input signal (typically a voltage or current) is applied to the coil, the relay opens or closes one or more contacts — allowing or interrupting the flow of current in a separate circuit. This makes relays ideal for controlling high-power loads with low-power signals, and for isolating control circuits from power circuits.
Main Types of Industrial Relays
1. Thermal Overload Relays
Thermal overload relays protect motors from damage caused by sustained overcurrent. They work by measuring the heat generated by excess current through bimetallic strips, which trip the relay when a set threshold is exceeded.
Typical applications: Motor starter protection, pump and conveyor control.
Examples from our stock:
- Telemecanique LR2 D1307 Thermal Overload Relay 1.6–2.5A
- Telemecanique LR2 D1321 Thermal Overload Relay 12–18A
- Telemecanique LR2 D3357 Thermal Overload Relay 37–50A
2. Safety Relays
Safety relays are designed for use in functional safety applications according to standards such as IEC 62061 and ISO 13849. They feature redundant internal contacts and self-monitoring to ensure fail-safe operation, making them mandatory in many machine guarding and emergency-stop circuits.
Typical applications: Emergency stop, light curtain monitoring, two-hand control, door interlocking.
Example from our stock:
3. Timer Relays (Time Delay Relays)
Timer relays add a configurable time delay to relay switching. They can be set to operate on-delay, off-delay, interval, or multifunction modes depending on the application.
Typical applications: Star-delta motor starters, sequential process control, lighting control.
Examples from our stock:
- Brodersen UNIC XM Timer Relay 12–240V AC/DC Multifunction
- Brodersen UNIC XMW Timer Relay 12–240V AC/DC Multifunction
4. Control Relays (Monitoring Relays)
Control and monitoring relays supervise electrical parameters such as voltage, current, phase sequence, and phase loss. They trip the circuit or send an alarm signal when values fall outside acceptable limits.
Typical applications: 3-phase motor protection, generator monitoring, HVAC systems.
Example from our stock:
5. Motor Overload Relays
Similar to thermal overload relays but often designed as standalone units for motor protection without a contactor assembly.
Example from our stock:
How to Choose the Right Industrial Relay
When selecting a relay for your application, consider these key parameters:
- Coil voltage: Match the relay coil voltage (e.g., 24VDC, 230VAC) to your control circuit.
- Contact rating: Ensure the contacts can handle the load current and voltage in the switched circuit.
- Number of contacts: Select NO (normally open), NC (normally closed), or changeover contacts as required by your circuit design.
- Application type: Safety-critical applications require certified safety relays; general automation can use standard control relays.
- New vs. used: For critical applications, new relays are preferred. For non-critical or retrofit projects, tested used relays offer significant cost savings.
New and Used Industrial Relays at KLJ Trading
At KLJ Trading, we stock both new/unused and used/tested industrial relays from leading manufacturers including Telemecanique, Schneider Electric, Pilz, Brodersen, and Moeller. All used items are tested before listing.
Browse our full range: Relays & Contactors Collection
Looking for a specific relay not listed? Contact us — we source components across Europe.