If you work with industrial control panels, HVAC systems, or automation equipment, chances are you’ve met a compact little workhorse very similar to the Schrack RP420024 relay. This 24 V DC, DPDT power relay combines solid switching capacity, strong isolation, and a small PCB footprint, making it a favourite in countless legacy and new designs. In this blog, we’ll unpack what makes the Schrack RP420024 relay special, how the Eurotek support assembly fits into the picture, and how it compares to modern alternatives so you can decide if it still deserves a place in your projects.
What Is the Schrack RP420024 Relay?
At its core, the Schrack RP420024 relay is a general-purpose, PCB-mount power relay from the RPII/2 series by TE Connectivity (Schrack). It uses a 24 V DC coil to actuate two change-over contacts (DPDT, or “2 Form C”), giving you flexible switching for control, interlocking, and small-motor applications. Rated at 8 A per contact at 250 V AC (and up to 10 A per UL at +70 °C), this relay bridges the gap between small signal relays and bulkier power contactors, which is why the Schrack RP420024 relay has been so widely adopted in control panels and OEM equipment.
Unlike solid-state relays, the Schrack RP420024 relay provides true galvanic isolation using mechanical contacts. That means it physically separates the control side (coil) from the load side (contacts), which many designers still prefer for robustness and predictable failure modes. It’s flux-proof (IEC RT II), so it can handle wave soldering and occasional condensation on the PCB. For users handling repair or retrofit work, understanding what’s inside the Schrack RP420024 relay helps you source equivalent replacements and avoid mismatches in ratings or pin patterns.
Key Electrical Specifications of the Schrack RP420024 Relay
When choosing any relay, electrical ratings are the first stop, and the Schrack RP420024 relay delivers a balanced spec sheet. The coil is designed for a nominal 24 V DC with a resistance of roughly 1100 Ω, which translates to around 21.8 mA of coil current and about 0.5 W of coil power. That’s modest enough for low-power control circuits, yet strong enough to ensure reliable pull-in even in noisy environments. Pick-up typically occurs around 16.8 V, with drop-out near 2.4 V, giving good margin for brownouts and wiring losses.
On the contact side, the Schrack RP420024 relay provides two change-over (DPDT) contacts. Each pole is rated for 8 A at 250 V AC, with UL allowing up to 10 A at 70 °C in some use cases. The maximum making current is around 14 A for a short duration (typically 4 seconds at 10% duty), and the switch can handle up to roughly 2000 VA of load. AC switching up to 400 V is supported, while the recommended DC switching limit is much lower—around 30 V DC according to UL data—so higher DC loads may require a different relay or additional protection.
Contact material on standard versions of the Schrack RP420024 relay is usually silver-cadmium oxide (AgCdO) or silver-nickel, sometimes with a gold flash depending on the variant. AgCdO is known for excellent endurance with inductive loads, but cadmium is a substance of very high concern under EU REACH, which is one of the reasons some designers prefer newer AgNi-only variants. Operate and release times are fast enough for most control tasks—typical values are around 9 ms for pull-in and 3 ms for drop-out, with 2–3 ms of contact bounce.
Mechanical Design and Footprint of the Schrack RP420024 Relay
From a mechanical standpoint, the Schrack RP420024 relay is compact and easy to integrate. The package is a through-hole PCB module measuring about 29 mm in length, 12.6 mm in width, and 25.5 mm in height, with a typical weight of roughly 18 g. That small footprint allows you to pack several of these relays into a tight control board without resorting to bulky contactors or external wiring. The pins are arranged in a standard RPII/2 pattern, with two coil pins and six contact pins, forming the familiar DPDT layout.
The pinout of the Schrack RP420024 relay is straightforward: two terminals for the coil (commonly labelled A1 and A2) and two sets of COM, NO, and NC for the contacts. Designers can either solder the relay directly into the PCB or plug it into a compatible socket. Because the housing is flux-proof rather than fully wash-tight, it tolerates wave soldering and some cleaning processes, but you should still follow best practices to avoid trapping contaminants near the pins. Keeping enough creepage around the solder pads helps you preserve the relay’s high isolation rating in the finished assembly.
Isolation, Safety, and Standards Compliance of the Schrack RP420024 Relay
One of the strengths of the Schrack RP420024 relay is its excellent isolation between coil and contacts. Dielectric strength is around 4 kV RMS between coil and contact set, with clearance/creepage distances of approximately 8 mm. That level of isolation means the relay can safely sit between low-voltage control logic and mains-rated circuits, a must for compliant industrial control panels and HVAC controllers. Additional dielectric ratings include about 1000 V RMS across open contacts and roughly 2500 V RMS between adjacent contacts, which helps reduce the risk of flashover in multi-pole switching situations.
The insulation system used in the Schrack RP420024 relay meets UL 94 V-0 requirements for flammability, and the relay is tested according to IEC 60664 and related standards for overvoltage category III and pollution degree 3. Approvals include VDE, UL, and cURus, making it suitable for installation in UL508A industrial control panels and similar equipment worldwide. When you specify the Schrack RP420024 relay in a certified panel, you’re relying on a device that’s been evaluated for creepage, clearance, dielectric performance, and environmental tests under IEC 60068.
Environmental Performance of the Schrack RP420024 Relay
In real-world environments, the Schrack RP420024 relay faces temperature swings, vibration, shock, and occasional moisture. The datasheet specifies an operating range from approximately –40 °C to +70 °C, which covers most industrial and building-automation scenarios, including cold plant rooms and warm electrical cabinets. Storage temperatures are not always explicitly stated, but similar devices typically handle –40 °C to +85 °C without issue, and the construction of the Schrack RP420024 relay is in line with that expectation.
Mechanical robustness is another strong point of the Schrack RP420024 relay. Functional shock resistance is around 30 g, while destructive levels can reach roughly 100 g, showing that the relay can survive transport and installation shocks as long as it’s properly mounted. Vibration resistance covers the 10–500 Hz range at about 11.5 g for functional use. That’s more than adequate for typical control panels, HVAC systems, small machinery, and similar installations. Flux-proof sealing to RT II protects the interior from solder flux and light condensation, although it doesn’t turn the relay into an outdoor-grade IP-rated device; you’ll still want proper enclosure design.
Soldering for the Schrack RP420024 relay is likewise straightforward: wave-solder processes up to around 260 °C for short durations are supported, with care taken to avoid excessive thermal stress. That makes the relay suitable for standard PCB assembly lines using through-hole soldering, whether automated or manual, and supports long-term reliability by keeping pin integrity intact.
Reliability and Lifetime Expectations of the Schrack RP420024 Relay
Reliability is critical if you’re using the Schrack RP420024 relay in 24/7 applications such as HVAC control, building automation, or industrial processes. Mechanical life is specified at well over 20 million operations, which means the moving parts can operate millions of times even under light loads. Electrical life is lower, as you’d expect: around 100,000 operations at 8 A, 250 V AC according to IEC test conditions, and about 6,000 operations at 10 A, 250 V AC at 70 °C under UL conditions. Those figures highlight why proper derating is so important in the design stage.
If you run the Schrack RP420024 relay at reduced current, avoid heavy inrush, and design with snubbers or varistors for inductive loads, you can extend the electrical lifetime significantly. While the manufacturer does not always provide a formal MTBF value, comparable relays show mean time between failures in the million-hour range for normal use. The combination of a robust coil system, quality contact materials, and tight manufacturing tolerances helps the Schrack RP420024 relay remain a dependable choice, especially in installed bases where thousands of these devices are already in service.
Typical Applications for the Schrack RP420024 Relay
The versatility of the Schrack RP420024 relay comes from its DPDT contact arrangement and solid 8 A rating. You can use the relay to switch single-phase AC loads, control small motors, actuate heaters, or route control signals between different parts of a system. In HVAC equipment, it often appears in air-handling units, fan-coil controllers, and compressor control boards, where its isolation and compact size are major advantages. The double-pole, change-over configuration also makes it ideal for reversing the direction of small DC motors or switching between redundant circuits.
In industrial automation, the Schrack RP420024 relay is common in PLC output boards, signal interlocking, and alarm circuits. It can be used to drive pilot lamps, interpose between low-power logic and higher-current devices, or switch between normal and emergency power feeds for small auxiliary circuits. Security systems, building-management systems, and power supplies also benefit from the relay’s combination of coil voltage, isolation, and manageable size. Since many older panels were built around this device, knowing its characteristics helps technicians select compatible replacements during maintenance.
Understanding the Eurotek Support Assembly for the Schrack RP420024 Relay
The phrase “Eurotek support assembly” can be confusing if you encounter it on a label or parts list alongside the Schrack RP420024 relay. In practice, this usually refers to a relay mounted on a dedicated base or socket—often a DIN-rail or PCB support assembly that makes wiring and replacement easier. TE Connectivity offers compatible Schrack sockets such as the RT78625, an 8-pin DIN-rail socket with screw terminals that matches the RPII/2 relay footprint. Eurotek may supply an assembly that combines this socket with the relay as a single unit.
By using a socketed Schrack RP420024 relay instead of soldering it directly to the board, you gain several advantages. Maintenance becomes simpler, because a failed relay can be swapped without desoldering; only the relay is replaced, not the entire PCB. Wiring is also more flexible—technicians can land field cables directly on the socket terminals, while the PCB holds only low-voltage logic. This makes the Eurotek support assembly a handy option for panel builders who need rapid field replacement and clear terminal labelling.
When ordering, make sure that your Eurotek or TE socket matches the pin pattern and current rating of the Schrack RP420024 relay. Some sockets are manufacturer-specific and may not accept alternative brands with slightly different dimensions. Checking the datasheet for pin spacing, terminal tightening torque, and mounting method (snap-on DIN-rail vs. screw-fixed) ensures that your support assembly is safe and long-lasting in the final installation.
Alternatives and Cross-References to the Schrack RP420024 Relay
Because the Schrack RP420024 relay is now considered obsolete or “not recommended for new designs” by many distributors, it’s wise to know which alternatives can step into the same role. The original document compares the RP420024 with several DPDT 24 V DC relays, including TE’s own RP421024, the Finder 40.52.9.024.0000, the Omron G2R-2 DC24, and a Panasonic DK2A-24V unit. All of these share 24 V DC coils and DPDT contacts, but their ratings, sizes, and materials differ.
The RP421024 is essentially a modern twin of the Schrack RP420024 relay, using silver-nickel contacts instead of silver-cadmium oxide. It keeps the same 8 A rating at 250 V AC, the same 0.5 W coil, and identical mechanical dimensions, which makes it ideal if you want a drop-in replacement with more environmentally friendly contact material. The Finder 40.52 series relay is another strong candidate; it also offers 8 A DPDT contacts and 24 V DC coils, but includes higher impulse isolation (around 6 kV) and slightly different physical dimensions, including a 5 mm pin pitch.
For lighter loads, the Omron G2R-2 DC24 can replace the Schrack RP420024 relay in designs that only require around 5 A per contact. It is narrower and may fit more easily into tight spaces, though it may not align with existing sockets. Panasonic’s DK2A-24V provides another 8 A DPDT option in a smaller form factor; however, you’ll likely need a different socket and may have to adjust PCB footprints. Whenever you substitute for the Schrack RP420024 relay, always confirm contact rating, coil power, pin layout, and socket compatibility before committing to a redesign or field replacement.
Wiring and Design Tips for the Schrack RP420024 Relay
Good wiring practice is essential to get the most out of the Schrack RP420024 relay. Start by feeding the coil with a stable 24 V DC supply, preferably from a regulated source. If you drive the coil from a transistor or PLC output, remember to use a flyback diode, RC snubber, or TVS device across the coil, depending on the nature of your driver. This protects both the switching device and the relay coil, while reducing EMI. Proper suppression also contributes to longer contact life and fewer nuisance resets in nearby electronics.
On the load side, treat the Schrack RP420024 relay like any other power switch. Inductive loads such as motors, solenoids, and contactor coils create voltage spikes when turned off, so they also benefit from snubbers, MOVs, or RC networks to tame transients. Keep the high-voltage and low-voltage wiring physically separated as much as your enclosure allows, preserving the 8 mm creepage from coil to contact that the relay offers internally. It’s also good practice to torque terminal screws correctly when using a DIN-rail socket, preventing hot spots or intermittent contacts over time.
Labelling each pole of the Schrack RP420024 relay clearly in your schematics helps technicians during commissioning and troubleshooting. For example, dedicate one pole to live switching and the other to a feedback circuit, or use both poles in series for additional isolation when working with higher-risk loads. Designing with clear function blocks and noting the relay’s ratings near the symbol keeps future maintenance in mind, especially in large panels where many similar relays coexist.
Availability, Pricing, and Lifecycle of the Schrack RP420024 Relay
As with many long-running components, the Schrack RP420024 relay has gradually transitioned into an “obsolete” or limited-availability status at mainstream distributors. Major catalogues list it as NRND (Not Recommended for New Designs), and stock tends to show up at surplus suppliers or specialist distributors rather than the usual big-box component houses. Prices vary depending on region and condition, but documented examples show new old stock in roughly the US$15–20 range per piece, with bulk purchases occasionally lowering the unit cost.
For panel builders working with existing equipment, sourcing genuine Schrack RP420024 relay units can still make sense, especially when the cost of redesigning PCBs or sockets is high. In new designs, however, it’s often smarter to choose a current production relay like the RP421024 or an equivalent from Finder, Omron, or Panasonic. These alternatives provide similar performance without depending on dwindling stock. Comparison tables in technical references give a helpful side-by-side view of coil power, contact material, isolation, and dimensions, making it easier to select a compatible part.
When you decide whether to continue using the Schrack RP420024 relay, consider more than just price. Lifecycle status, regulatory requirements (for example, around cadmium content), spare-parts availability, and socket compatibility all play a role. Planning your transition from legacy relays to modern equivalents ahead of time avoids rushed replacements, unexpected downtime, or mismatched parts when a large batch of relays reaches end-of-life simultaneously.
How the Schrack RP420024 Relay Fits Into Modern Designs
Even though the Schrack RP420024 relay is not a “latest-generation” part, it still fits comfortably into many modern control strategies. Its 24 V DC coil integrates well with PLC logic levels and distributed I/O systems, and its 8 A DPDT contacts are ample for pilot loads, small motors, and control transformers. The relay can act as a reliable interface between sensitive electronics and the harsher world of mains circuitry, and its mechanical life rating means it can survive frequent switching in energy-management or alarm systems.
However, designers today must also account for evolving safety standards and environmental regulations. Where cadmium-based contacts are a concern, an AgNi alternative is often preferred. That’s where cross-compatible parts like RP421024 come in, offering nearly identical behaviour to the Schrack RP420024 relay but with updated materials. In systems where higher isolation, wash-tight sealing, or surface-mount options are needed, on the other hand, it may be worth migrating to a newer relay platform entirely, using the Schrack RP420024 relay as a benchmark for required ratings while exploring more advanced families.
Related Product Collections
If you’re exploring the Schrack RP420024 relay and similar devices, these related product collections from Industrial Electrical Warehouse can help you find compatible and complementary parts:
- Control Relays (Motor Control Equipment) →
Browse control relays specifically geared toward motor control, interlocking, and logic functions—including assemblies that feature the Schrack RP420024 relay and comparable units for new designs and retrofits. - Relays for Power Distribution →
A broad collection of general-purpose, solid state, and plug-in relays designed for power distribution, control, and signalling applications, well suited to projects where the Schrack RP420024 relay might be one of several relay types in the same panel. - Safety & Control Relays →
Safety relays, safety contactors, and associated control devices that integrate with or complement standard control relays when you’re building emergency-stop circuits, interlocks, and machine safety systems.
Conclusion: Is the Schrack RP420024 Relay Right for Your Panel?
If you’re maintaining existing equipment that already uses the Schrack RP420024 relay, keeping a small stock of genuine units—or carefully vetted equivalents—remains a practical strategy. Its combination of 24 V DC coil, 8 A DPDT contacts, solid 4 kV isolation, and proven field history makes it a dependable component, especially when paired with the Eurotek support assembly or compatible DIN-rail sockets. In new designs, though, it’s usually wise to treat the Schrack RP420024 relay as a reference point and consider modern, RoHS-friendly relatives with the same footprint and ratings.
Ultimately, the choice comes down to your application, regulatory needs, and long-term service plans. Reviewing the detailed specifications, environmental data, and alternatives outlined here should help you decide whether to keep the Schrack RP420024 relay in your BOM or shift to a newer family. When you’re ready to compare options, visit the product page for the Schrack RP420024 relay and its Eurotek support assembly so you can confirm compatibility, review live stock, and make a confident decision for your next build or retrofit.
