Interface module for PLC and DCS I/O: relay and system-cable interface modules on DIN rail
DIN-rail I/O interface modules · 6.2 mm relay and SSR interface modules, passive system-cable (IDC) breakout modules for PLC and DCS cabinets
An interface module is a DIN-rail device in a control cabinet that sits between a PLC or DCS I/O card and the field wiring: either a relay or solid-state relay module that isolates the controller from field loads and switches them, or a passive module that takes a multi-core system cable or ribbon cable from the I/O card and breaks it out to individual terminals. Ask three things first: whether each channel must isolate and switch or only connect, what load (voltage, current, AC or DC) each output switches, and how the module connects to the controller (single wires or a system cable).
DIN-rail interface modules for controller I/O in PLC and DCS cabinets: slim relay and SSR interface modules and passive system-cable or IDC breakout modules. Camera data interfaces (GigE, CoaXPress, Camera Link) are covered on the Line scan camera page; networked remote I/O on the Remote I/O module page; single terminal blocks on the Terminal block page; plug-in power relays on the Power relay page.
CNFX editorial research · Sources checked October 12, 2026 · 3 sources
Finder's 38 series relay interface modules are 6.2 mm wide on 35 mm rail (EN 60715), with integral coil indication and protection circuit, and are described by Finder as an interface for PLC and electronic systems. The 38.51/38.61 electromechanical version has one changeover contact rated 6 A (10 A peak) at 250 V AC (400 V maximum switching), AC1 1,500 VA, AC15 300 VA at 230 V, DC1 breaking capacity of 6, 0.2 and 0.12 A at 24, 110 and 220 V, and a minimum load of 500 mW (12 V/10 mA). [1]
The same module lists 10 million mechanical cycles and 60,000 electrical cycles at rated AC1 load, 5/6 ms operate/release time, 6 kV (1.2/50 µs) insulation between coil and contacts with 8 mm spacing, 1,000 V AC across open contacts, −40 to +70 °C for coils up to 60 V, and IP20. [1] The solid-state 38.81/38.91 versions offer outputs of 6 A at 24 V DC, 0.1 A at 48 V DC or 2 A at 240 V AC, with 2,500 V AC input-to-output dielectric strength and −20 to +55 °C. [1]
Editorial calculation: DC1 breaking capacity drops from 6 A at 24 V DC to 0.12 A at 220 V DC, a factor of 50, so a DC load above 24 V needs checking against the DC curve, not the AC rating; and 16 modules at 6.2 mm occupy about 99 mm of rail.
Give the supplier the controller (PLC or DCS model and I/O card), number of channels, input or output, control voltage, field load type, voltage and current per channel, AC or DC, switching frequency, isolation required, terminal type (screw or push-in), cabinet temperature, and whether a system cable connects the card.
02
Break out a system cable with a passive interface module
Hongfa describes its interface modules as housings with connectors and interfaces that connect external cables and convert between them, for easy installation and tidy wiring in DCS and industrial automation equipment. [3] ASI's IMRC20 is a DIN-rail module that takes a 20-pin IDC ribbon-cable connector with locking latches to two-level screw terminals, rated 2 A and 120 V AC, accepting 26 to 12 AWG wire, with six component holes in series between connector and terminals for resistors, diodes or MOVs. [2]
The ASI page also refers to a 10-pin cable and a 10-position connector in two places while naming the product as 20-pin; confirm the pin count with the supplier before ordering. [2] Editorial note: a passive breakout carries the I/O card's own signals and does not isolate them, so the card's channel rating, not only the module's 2 A, sets what each terminal may carry.
03
One relay interface family, five output builds
Finder's 38 series overview shows how far a single interface-module family stretches by width and output. [1]
Special versions of the 6.2 mm modules add coil or input leakage current suppression. [1]
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Controller: [PLC or DCS; I/O card]
Channels: [number; input or output]
Control side: [voltage; system cable or wires]
Field side: [load; voltage; current; AC or DC]
Isolation: [required; kV]
Terminals: [screw, box clamp, push-in; wire range]
Cabinet: [temperature; rail space]
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
How wide is a slim relay interface module?
Finder's 38 series modules are 6.2 mm wide, rated 6 A at 250 V AC with one changeover contact. [1]
Can a relay interface module switch DC loads?
Yes within its DC rating; Finder's 38.51 lists DC1 breaking capacity of 6 A at 24 V but 0.12 A at 220 V. [1]
What is a system-cable interface module?
A passive module that connects a multi-pin cable from the I/O card to terminals; ASI's IMRC20 takes a 20-pin IDC cable at 2 A and 120 V AC. [2][3]
Sources and what still needs a direct check
Sources checked 2026-10-12. Relay and SSR module data come from Finder's 38 series catalogue; the passive breakout data from ASI's product page; Hongfa's category page describes its system-cable interface modules. Values apply to the models named; confirm ratings for the module you buy.
