ABB CR-P, CR-M and CR-U Interface Relays Review

What is the ABB CR interface relay range? The ABB CR range covers pluggable interface relays for control-circuit switching, organized into three families — CR-P, CR-M and CR-U — each covering a different mix of mounting format, contact count and current class, built to IEC 61810 and IEC 60947-5-1. Pick the wrong family and a panel builder either pays for contact current the design will never use, or under-specs a relay driving a contactor coil that actually needs the extra headroom. This review works through CR-P's compact pluggable format, CR-M's step up in contact current, CR-U's universal-socket positioning, the shared LED and suppression accessories, and a straight comparison to help pick between them for a PLC-driven control panel.

The ABB CR Range at a Glance

ABB groups its pluggable interface relays under the CR prefix. CR-P, CR-M and CR-U are the current members, and all three plug into a matching DIN-rail socket rather than terminating field wiring directly on the relay. That single design choice is why interface relays exist as a category: a technician pulls a failed CR-P out of its socket and clips in a replacement in under a minute, no rewiring, no re-torquing of field terminals. CR-P is the compact format aimed at panel density — PCB and DIN mounting, 1 to 4 CO contacts. CR-M carries a higher contact current for loads a step above small pilot duty, contactor coils and solenoid valves among them. CR-U sits alongside both as a broader-compatibility universal range, built for jobs where socket footprint and cross-family replacement matter as much as the relay's own spec. All three sit under the same standards and terminology the interface and coupling relay engineering guide covers in more depth.

CR-P — Pluggable Interface Relays for PCB and DIN Mounting

CR-P is ABB's compact pluggable interface relay, offered from 1 CO up to 4 CO on a matching CR-P socket. It targets the same job most interface relays handle: taking a 24 VDC signal off a PLC output card and switching a load the PLC output itself cannot carry directly. Coil options run 24 VDC as the workhorse rating, with AC coil variants available where the control circuit is already AC. Contact ratings sit in the small-pilot-duty range typical of interface relays — a few amps AC1 — which is enough for a contactor coil or an indicator lamp but not for switching a motor branch circuit.

That coil power number matters at panel design stage, not just at commissioning. A CR-P coil draws a few hundred milliwatts continuously once energized, and on a densely packed DIN rail with thirty or more relays that adds up as heat inside an enclosure with no forced ventilation. Slim-format panels running high channel counts feel this more than a sparsely populated cabinet does.

CR-M — Industrial Plug-in Relays for Higher Current Control

CR-M moves up from CR-P's small-pilot-duty contacts to a heavier contact current class, still in 2 to 4 CO arrangements, still on its own dedicated socket. This is the family to reach for when the load is not a small indicator or a low-power sensor input but a genuine contactor coil with real inrush, or a solenoid valve bank drawing more than CR-P's contacts are rated to break. Breaking capacity on the DC side falls off sharply as voltage climbs — there is no natural current zero-crossing on DC to help the arc self-extinguish — so a CR-M contact rated comfortably at 24 VDC is not rated the same way at 110 VDC. Check the DC breaking curve, not just the AC1 number on the label.

What we see in the field: teams size CR-M by the load's steady-state current and then get caught out by contactor coil inrush, which for AC contactor coils can run several times the holding current for the first cycle. A CR-M relay that handles the holding current fine can still see its contacts pitted over enough switching cycles if it is sized against the coil's holding rating rather than its inrush rating.

CR-U — The Universal Plug-in Range

CR-U is positioned as ABB's broader-compatibility plug-in range, built around socket footprints intended to cover more replacement scenarios than a single CR-P or CR-M line. It fits where a panel builder is maintaining a mixed installed base — some legacy sockets, some newer CR-family sockets — and wants one relay family that closes more of the gap without stocking three separate part sets. The functional building blocks are the same as CR-P and CR-M: an electromechanical relay, a socket carrying screw or push-in terminals, an optional LED status module, and a coil-suppression module for DC coils.

This depends on what a given panel actually needs replaced. If a shop is opening new cards on a clean sheet, CR-P or CR-M — whichever fits the contact current — is usually the simpler spec because it is the narrower, better-documented range. CR-U earns its place on retrofit and maintenance jobs where socket compatibility across an existing installed base outweighs picking the theoretically tightest-fit relay.

Sockets, LED Modules and Coil Suppression Across the CR Family

Every CR-P, CR-M and CR-U relay ships as a pair with its socket, and the socket carries the terminal type, the retaining clip and, in some cases, the current rating ceiling for the pair — not the relay alone. Screw terminals are the familiar option: cheap, re-torquable, easy to inspect during a panel audit. Push-in terminals wire faster and hold up better under vibration, which matters on skid-mounted or mobile equipment where a screw terminal can work loose over time. Both terminal styles are available across the CR range depending on the specific socket part chosen.

Skip the diode on a DC coil driven by a PLC transistor output and the transistor takes the hit instead. The coil's collapsing magnetic field generates a reverse voltage spike well above the supply rail the instant the drive current stops, and a transistor output with no clamping path across the coil absorbs that spike until it fails, sometimes on the first cycle, sometimes weeks in. ABB's suppression modules clip into the socket alongside the LED module, so adding one to an already-installed CR-P or CR-M does not require rewiring the coil circuit. This is one part of the broader isolation job interface relays do between a PLC output card and the field load it drives.

Choosing Between CR-P, CR-M and CR-U

The three families overlap enough in contact count that the deciding factor is usually current class and installed-base compatibility rather than contact arrangement alone.

Cross-check the socket rating against the relay before finalizing a bill of materials; the socket, not the relay datasheet alone, sets the real ceiling once the pair is assembled. For guidance on matching coil voltage and contact count to a specific PLC output card, see how to select an interface relay for PLC outputs, and for the underlying contact layouts across CO counts, SPDT, DPDT and 4PDT contact configurations covers the trade-offs directly. Stocked CR-family relays and sockets sit in Stoklink's interface and control relays collection; where the switched load is a motor branch rather than a coil, pair the interface relay with a contactor sized for the motor current, not the CR relay's own contact rating.

Conclusion

CR-P, CR-M and CR-U cover the same interfacing job at three different points: compact high-density PLC panels, higher-current contactor and solenoid loads, and mixed-installed-base retrofit work. Match the family to the load's actual current class and inrush behavior, fit the correct suppression module on every DC coil, and check the socket rating alongside the relay before the bill of materials is final. For the broader interfacing concepts these three families share with other brands' equivalents, the interface and coupling relay engineering guide lays out the shared standards and terminology in one place.