Overview
What are Relays & Timing Relays?
Relays are electrically operated switches used to control a high-power circuit with a low-power signal. They provide essential electrical isolation between control logic (such as a PLC output) and field devices like motors, heaters, or solenoid valves. Timing relays expand on this functionality by adding a time-delay element, allowing for precise control over when a circuit opens or closes relative to a trigger signal.
In industrial automation, these components are the fundamental building blocks of hardware logic. While PLCs handle complex software-based logic, relays are often used for physical interlocks, emergency stop circuits, and signal amplification where direct PLC output current is insufficient.
Main Manufacturers
PALM Parts Solution carries a comprehensive inventory of relays and timing relays from the industry's most trusted brands:
- Allen-Bradley: Known for high-durability industrial relays and specialized safety components.
- ABB: Offers a wide range of electronic timers and measuring/monitoring relays.
- Siemens: Provides integrated solutions for cabinet mounting with high switching reliability.
- Schneider Electric: Highly versatile ranges suitable for both infrastructure and industrial machines.
- Omron: Specialists in high-speed solid-state relays and miniature PCB-mount relays.
- Bosch Rexroth: Focused on high-performance relays for hydraulic and motion control systems.
- GE Fanuc: Reliable legacy and modern relay components for CNC and PLC systems.
Typical Applications
Relays and timing relays are found in almost every automated electrical system:
- Motor Control: Using timing relays for Star-Delta starting to reduce inrush current.
- Safety Interlocks: Ensuring a machine cannot start unless all guards are closed (Safety Relays).
- Sequencing: Staggering the activation of multiple pumps or fans to prevent power surges.
- Isolation: Protecting sensitive PLC outputs from high-voltage transients in the field.
- Lighting Control: Utilizing timing relays for scheduled or delayed-off illumination in industrial facilities.
Popular Product Families
We stock several industry-standard product lines to ensure your systems remain operational:
- Allen-Bradley: 700-HL Terminal Block Relays, 700-HP General Purpose Relays, and 700-FS Timing Relays.
- Siemens: SIRIUS 3RP Timing Relays and SIRIUS 3RQ Coupling Relays.
- Schneider Electric: Zelio Relay (RXM, RUM, RPB) and Harmony Timer Relays.
- ABB: CT-S and CT-D Range electronic timers and CR-M Miniature Interface Relays.
- Omron: MY Series (General Purpose), G2R Series, and H3CR Series Timers.
Replacement & Compatibility
Finding replacements for relays is generally efficient due to standardized mounting and pinout configurations. Many 'Ice Cube' relays (8-pin or 11-pin) are interchangeable across brands like Allen-Bradley, Omron, and Schneider, provided the coil voltage and contact ratings match.
When migrating from legacy GE Fanuc or older Bosch Rexroth systems, it is vital to check the footprint of the relay socket. If a direct drop-in is not available, modern DIN-rail mounted slimline relays (6mm width) from Siemens or ABB are often used to modernize panels and save significant cabinet space. Always verify terminal labeling, as NO/NC positions can vary between budget and premium manufacturers.
Selection Guide
To select the appropriate relay or timing relay, verify the following technical specifications:
- Coil Voltage: Common industrial standards include 24VDC, 120VAC, and 230VAC.
- Contact Configuration: Determine if you need SPDT (1 C/O), DPDT (2 C/O), or 4PDT.
- Load Rating: Ensure the contact current rating (Amps) exceeds the maximum steady-state and inrush current of the load.
- Timing Function: Identify if the application requires On-Delay, Off-Delay, Flasher, or Multi-function timing.
- Mounting Style: Specify DIN rail, Panel Mount, or PCB Mount.
- Environmental Factors: For high-vibration or corrosive environments, consider sealed or hermetically protected relays.
62 products · Allen-Bradley
Frequently asked questions
What is the difference between an electromechanical relay and a solid-state relay?
Electromechanical relays use a physical coil to move mechanical contacts, whereas solid-state relays (SSRs) use semiconductor devices like thyristors or transistors. SSRs offer faster switching speeds, silent operation, and a longer lifespan due to no moving parts, making them ideal for high-frequency switching. However, electromechanical relays are generally more robust against voltage surges and provide physical isolation between the control circuit and the load.
How does a timing relay differ from a standard control relay?
Timing relays incorporate an internal timer to delay the opening or closing of contacts. Functionalities include 'On-Delay' (timer begins when power is applied, contacts switch after a set duration) and 'Off-Delay' (timer begins when power is removed, contacts remain switched for a set duration). These are essential for sequencing motors, managing conveyor start-ups, and preventing simultaneous high-inrush current loads.
What is the difference between SPDT and DPDT relay configurations?
Single-pole, double-throw (SPDT) relays have one common terminal and two contact positions (one normally open, one normally closed), allowing the switching of one circuit between two paths. Double-pole, double-throw (DPDT) relays consist of two identical SPDT sets controlled by a single coil, allowing the simultaneous control of two independent circuits. This is useful for reversing motor polarity or controlling separate signal and power lines.
How do I choose the correct contact rating for a relay?
When selecting a relay, you must match the coil voltage (e.g., 24VDC, 120VAC) to your control system output. Equally critical is the contact rating, which must exceed the load current (Amps) and voltage. For inductive loads like motors or solenoids, ensure the relay is rated for high inrush currents, or use a snubber circuit to prevent contact arcing and premature failure.
Can I replace an Allen-Bradley relay with a Schneider Electric equivalent?
Replacing a relay from a different manufacturer is generally straightforward if the pinout configuration (e.g., 8-pin or 11-pin circular, or blade-style) is identical. Standards like the DIN rail mounting system make physical compatibility easy. However, always verify that the coil power consumption and the contact's AC/DC breaking capacity match or exceed the original specifications to ensure system safety.
What do NO and NC mean in relay contacts?
A 'Normally Open' (NO) contact stays open and prevents current flow until the relay coil is energized. A 'Normally Closed' (NC) contact remains closed and allows current to flow until the coil is energized, at which point it opens. NO is typically used for start buttons/triggers, while NC is often used for stop buttons or safety interlocks.
What are the common signs of relay or timing relay failure?
Relay failure is often indicated by an audible 'clicking' sound without the load engaging, charring on the plastic casing, or visible pitting on the contacts. In timing relays, failure may manifest as inconsistent delay periods or a failure to reset. Using a multimeter to check for continuity across the contacts while the coil is energized is the standard diagnostic method.
Why should I use a safety relay instead of a general-purpose relay?
Safety relays use redundant internal circuits and force-guided contacts to ensure that a single component failure does not lead to a loss of safety function. Unlike standard relays, which can weld shut and remain 'on,' a safety relay is designed to detect such faults and prevent the machine from restarting until the fault is cleared.
Do timing relays support industrial communication protocols like Modbus or IO-Link?
Modern 'smart' timing relays and monitoring relays often include communication ports (such as IO-Link or Modbus) that allow them to transmit status data to a PLC. Standard electromechanical relays do not communicate via protocols; instead, their status is read by the PLC through digital inputs wired to the relay’s auxiliary contacts.
What are the benefits of DIN rail mounted relays?
DIN rail relays are designed to snap onto standard 35mm metal rails found in industrial control panels. This standardized mounting allows for high-density packing of components and simplifies the wiring and replacement process. Most industrial relays from ABB, Siemens, and Allen-Bradley utilize this format.