Beckhoff / EtherCAT junctions and Ethernet switches

You cannot branch an EtherCAT line with an Ethernet switch. EtherCAT is processed on the fly along a line, and a standard switch breaks that. Branching needs a junction: a CU1128, an EK1122, or a coupler with junction ports.

The Beckhoff CU range is the infrastructure between the controller and the I/O. Junctions, media converters, and the ordinary Ethernet switches that sit on the other network entirely.

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Two different networks, two different parts

The single most useful distinction on this page, and the reason wrong parts get ordered.

Both use RJ45 connectors and ordinary CAT cable, which is exactly why the mistake happens. A CU2008 fitted into an EtherCAT line looks like the right sort of device and the network simply does not come up.

Tell us which network the part sits on and we will not send the wrong one.

EtherCAT junctions

A junction lets an EtherCAT line split into branches while keeping the on-the-fly processing intact. Each branch is still a line; the junction manages where the frame goes and where it comes back.

CU against EK is where it mounts, not what it does

A CU1128 is a standalone box on the DIN rail. An EK1122 is a terminal that clips into a station between other terminals.

So the choice was usually made by cabinet layout. They are not substitutes for each other mechanically, even where the port count would suit.

If the existing part sits in the middle of a terminal rail, you need the EK. If it is a separate box with its own mounting, you need the CU.

EK1110 is an extension, not a junction

Easy to confuse and it does something different.

An EK1110 goes on the end of a station in place of the bus end terminal and carries the EtherCAT onward to the next station over a normal Ethernet cable.

A junction branches. An extension continues. If a rail ends in an EK1110 rather than an EL9011, that is why there is no end terminal on it and nothing is wrong.

Hot Connect

Worth knowing because it changes what a junction is doing on the machine.

Junction ports can be configured as Hot Connect groups, so a branch can be disconnected and reconnected while the rest of the system runs. That is how tool changers, removable stations and interchangeable format parts are done.

The behaviour is configured in TwinCAT, not set by the hardware. So a like-for-like junction goes in and works, and the configuration stays in the project where it belongs.

Media converters, and why an ordinary one will not do

The part most often substituted badly.

A generic Ethernet media converter is not an EtherCAT media converter. A generic one buffers the frame, which adds latency and disrupts the distributed clock synchronisation that EtherCAT motion depends on.

The symptom is not a dead network. It is jitter, clock warnings and motion that will not synchronise, which sends people looking at drives.

Multimode and singlemode are not interchangeable

CU1521 and CU1521-0010 differ by four characters and by the fibre they drive. Multimode covers a few hundred metres; singlemode covers kilometres.

Fit the wrong one and either the link does not come up at all, or it comes up and behaves badly over distance.

Tell us the fibre type and the run length.

Why fibre at all

Two reasons, and both come up in New Zealand plant.

The 100 m limit is per hop, not per network. A long line of devices each 100 m apart is fine. One 150 m run between two of them is not, and it will work intermittently rather than failing cleanly, which is worse.

If a link drops under load or in wet weather and the run looks long, measure it before replacing hardware.

Standard Ethernet switches

For the other network. These are ordinary unmanaged switches in industrial packaging.

These carry no configuration. A shelf unit is a working unit, and any equivalent industrial switch will physically do the job if the mounting suits.

The reason to buy the Beckhoff part is usually that the cabinet was built around its footprint and its 24 V connector, not because the switching is special.

Connectivity boxes

The CU8802 belongs to the display chain rather than the fieldbus, and it is covered on our industrial PC and panel page. It appears here because it carries a CU number and gets searched alongside the rest.

Cellular modules are band-specific. A unit sourced for another market may not work on New Zealand networks. Tell us it is going onto a local network and we will check the variant.

Before ordering a replacement

What to send us

The full part number. CU and EK numbers are short and unambiguous.

Which network it sits on. EtherCAT fieldbus or standard Ethernet.

Whether it is a standalone box or a terminal in a rail. That decides CU against EK.

For fibre, the mode, the connector and the run length.

The number of branches, if you are sizing a junction.

A photo of the cabinet. Beckhoff labels the front clearly and one photo usually identifies the whole arrangement.

What we can supply

Current production. CU1121, CU1123, CU1124 and CU1128 junctions, EK1122 junction terminals, EK1110 extensions, CU1521 and CU1561 media converters, EK1521 fibre terminals, CU2005, CU2008 and CU2208 switches, CU8802 transmitters and CU8210 adapters. Quoted with a delivered lead time.

Discontinued. Earlier CU and EK infrastructure variants. Surplus and tested used.

Cable and connectors. The ZB and ZK ranges, plus fibre patch leads made to length.

These are easy spares to hold

Worth stating because it is unusual for network infrastructure.

Junctions, extensions and media converters carry no user configuration. The topology lives in the TwinCAT project, and the hardware is addressed by where it sits.

So a like-for-like part goes straight in with no laptop and no software. One of each type you run covers every station on the site, which makes this a genuinely cheap thing to be covered on.

The exception is the fibre converter, where multimode and singlemode are different parts. Hold whichever your plant actually uses.

We buy Beckhoff infrastructure

CU and EK parts resell readily because they are self-identifying and carry no configuration. They are small, they are easy to overlook when a panel is stripped, and they are worth considerably more than scrap.

Keep junctions and converters with the station they served, and keep fibre converters in matched pairs. See Sell To Us.

Common questions

Can you get a part that is not listed on your site?
Usually. The site shows what we hold, not what we can source.

Can I use an ordinary switch to split my EtherCAT?
No. EtherCAT needs a junction. A switch breaks the on-the-fly processing.

What is the difference between a CU1128 and an EK1122?
Where it mounts. The CU is a standalone box, the EK is a terminal in a rail. Both are junctions.

Can I use a generic fibre converter?
Not on EtherCAT. It adds latency and disturbs distributed clocks, which shows up as motion faults rather than network faults.

Do you supply used equipment?
Yes, where new is not available, tested and clearly described.

What is the lead time?
Ex stock items ship the next working day within New Zealand. We give you a firm lead time with the quote.

Do you quote in NZD?
Yes, in NZD including GST for New Zealand customers.

Related

Beckhoff overview, EtherCAT Terminals, KL Bus Terminals and industrial PCs and panels.

For industrial networking from other brands see Siemens SCALANCE, Allen-Bradley Stratix and Phoenix Contact Factoryline.

Send us your part numbers

Tell us whether the part sits on the EtherCAT segment or on the plant network. Both use RJ45 and they need entirely different hardware. Quotes in NZD including GST.

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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 Beckhoff Automation. Beckhoff, TwinCAT, EtherCAT and CP-Link are trademarks of Beckhoff Automation. All trademarks, brand names and part numbers are the property of their respective owners and are used here for identification purposes only.