Phoenix Contact / Interface relays

PLC-INTERFACE is three separate order numbers. Knowing which one you need turns a module replacement into a relay replacement.

PLC-INTERFACE relay modules sit between PLC outputs and field devices in most New Zealand panels. They are 6.2 mm wide, DIN rail mounted, and they wear out on operation count like any relay.

The part you probably need is the cheapest one

This is the most useful thing on the page. A PLC-INTERFACE module is a base terminal block plus a plug-in relay, and each has its own order number.

If the relay has worn out, you need the REL-MR, not the whole module. The base stays on the rail with all its wiring intact and the relay unplugs from the top.

That is the difference between a quick swap and reterminating a wired module. On a panel with thirty interface relays it is a substantial saving.

And the reverse warning. Phoenix flags that the PLC-BSC needs further products for operation. Order the base alone expecting a working module and you have a terminal block with no relay in it.

How the designation decodes

Take PLC-RSC-24DC/21.

The coil voltage is in the number and it is a separate selection. 24DC is the common one but 120AC, 230AC and 24AC/DC versions exist. Fitting a 24 V DC relay where a 230 V coil was does nothing at all.

Screw versus push-in

The PLC-RPT-24DC/21 is the push-in equivalent: 24 V DC coil, 5 to 250 V AC/DC output load voltage, 6 A load, single pole double throw, with an operating voltage LED.

Match the base you already have. A push-in relay does not go into a screw base.

Confirmed specifications

The 6.2 mm width matters when planning rail space. It is the same width as a UT 4 terminal block, which makes mixed strips easy to lay out.

Bridging between modules

Where several interface relays share a common potential, Phoenix uses plug-in bridges rather than loop wiring.

Phoenix specifies that potential bridging between identical terminal blocks in adjacent modules is done with FBST 8-PLC or FBST 500 bridges.

Bridges are a separate order and always forgotten. If you are quoting a bank of interface relays, the bridges are part of the job.

Accessories

The ZB 6 markers are sized to the 6.2 mm width and snap into the tall marker groove. They can be printed on a plotter, so a panel builder can produce a labelled strip rather than hand-writing.

The SZF 1-0,6X3,5 doubles as the actuation tool for ST spring-cage terminals, so it is worth having in the toolkit if the panel has both.

Why interface relays exist

Worth stating because it explains what to check when they fail.

A PLC output typically switches a few hundred milliamps at 24 V DC. A contactor coil, solenoid or lamp often needs more, or a different voltage entirely. The interface relay bridges that: PLC-level coil, power-level contact.

It also protects the PLC output. The relay takes the inductive kick from the load instead of the output driver.

Which is why, if you are replacing both an interface relay and a PLC output module on the same circuit, the load probably needs suppression. Same argument as on our SM 322 and Omron relay pages.

What usually fails

The relay, not the base. Contacts erode on operation count. The base is a passive terminal block and rarely fails.

So hold relays, not modules. A box of REL-MR-24DC/21 is cheaper than a box of complete modules and covers the same failures.

If you run a maintenance store with Phoenix interface relays in the panels, that is the stocking decision worth making.

The wider Phoenix relay range

Solid-state versus relay is a real choice. The PLC-OSC and PLC-OPT solid-state modules have no contacts to wear, which suits high switching frequencies. A relay handles higher inrush and gives genuine isolation with a physical air gap.

If a mechanical interface relay is failing frequently, switching frequency is worth checking before fitting another one. A solid-state module may be the better answer.

What we can supply

Current production. The full PLC-INTERFACE range in screw and push-in, REL-MR relays, solid-state modules, bridges, markers and tools. Quoted with a delivered lead time.

Relays separately. If you only need the plug-in relay, say so and we will quote that rather than complete modules.

Bulk quantities. Interface relays are a consumable. Send us the list and we will quote the lot including bridges and markers.

Related

Phoenix Contact overview. Terminal blocks. Power supplies.

For relays from other brands see Omron MY and LY.

Send us your order numbers

Tell us whether you need the complete module, the base, or just the plug-in relay, because they are three different order numbers. Include the coil voltage. Quotes in NZD including GST.

Request a quote

Industech is an independent supplier of new, surplus and used industrial automation equipment. We are not an authorised distributor of, approved by, sanctioned by, or affiliated with Phoenix Contact GmbH & Co. KG. Phoenix Contact, PLC-INTERFACE and CONTACTRON are trademarks of Phoenix Contact. All trademarks, brand names and order numbers are the property of their respective owners and are used here for identification purposes only.