Problem with the wiring?


I have problems to connect in the Velbus Link.
It takes about 40 minutes to connect/scan the modules. Then working in the user interface is also very slow.
In some cases, when it is connected, the modules are still with a red cross and when I scan no module is discovered (they keep the red cross).

It was getting 'worse and worse" with the time… and I have the impression that it has become really much worse with the addition of the Home Center last week.

Can someone tell me what the problem might be?

Thank you


Are you connecting through USB or Home Center?

Indeed if no module is getting scanned there is usually a fault in wiring. Do you have exactly 2 terminators in your installation? Is there ashort between H and L in the bus wiring?

Aside from the Home Center have you changed anything else and does removing the Home Center help at all?

As a last resort, try splitting up your installation into smaller parts to check where a problem might be.

Best regards


The 40 minutes is with the USB connection.
It is slightly faster with the Home Center connection… but connecting with the Home Center, I get error messages telling that incorrect packages are received, which is surely due to a problem of wiring.

I don’t think the electrician put any terminator at all. I will try to put 2.
This would explain the slowliness of the connection… but would it explain also the incorrect packages received?

A short between H and L… I hope not… Would it still work even with a short between H and L ? I don’t notice any problem with any lamp or switch…

Thank you

Oh yes indeed.

You’d be amazed at the problems that echos and standing waves can cause.

Put at least 2 terminators in, as far apart as possible and if you have a long third leg (for example) it’s worth putting a terminator at the end of that too.

You might have to move terminators around until the delay time per message comes right down.
(The furthest right column in the VelbusLink log panel)

Good luck

Thank you

Where should I put terminators if the bus is a loop?

For the delay time, around what value is it acceptable?
I have a lot of messages with +300, +400 … and I have one module (a mini motion detector) for which the delay is very high +1300 sometimes +3000.


Good morning,

The rule still applies that the terminators should be “far apart”.

So one might suggest…

1 in your main cabinet and the other roughly half way around the loop?

As for delay times.

~400 ms is okay, it’s big but it’s okay.

Anything more is unusual.

Does that help?



Good afternoon Stuart,

Of course that helps. Thanks a lot.

Now I put terminators (always on an end of the bus). Some modules were discovered again. But screens started not to work. I put the terminator elsewhere, screen worked again. Etc…
I’m now in a situation where all modules work and are discovered again. But I still have very high value but for some modules (in the thousands… I even saw a 9999).
As you said, I will try to move the terminators around until it works… Not an easy thing…
If I don’t succeed, is there someone who could help me on-site (near Brussels) ?

Good morning,

That sounds a lot better already.

It may take some time for modules to calm down, especially if they have been waiting for a free slot on the bus for a while. (That sounds like public transport advice, rather than building control.)

As for someone you can call upon for ‘in person’ assistance, I’m certain you’ll be able to find someone local to you.

I only manage the UK, but there are plenty of people / companies listed on the Sales page for Belgium.

Good luck,


Good morning,

Thank you again for your reply.

You said that the terminators should be as far apart as possible. Is it in distance, or in number of modules in between? Indeed, I have a long loop. Half of the loop has modules. And then the other half is actually the return to the electric cabinet. So, between the last modules and the cabinet, the distance is long (probalby 30m) but there are no modules… If I put a terminator on the last module and in the cabinet, then I have no module in between.
How are the terminators used by the modules/the bus?

More generally my question would be to understand what is the effect of the terminator. I guess it does not mean that the messages are not propagated after that module… otherwise it would not work in a loop…

And when you say that it takes some time for the modules to calm down, how long do you have in mind? Does it mean that when I try to change a terminator, I have to wait some time to test the connection in VelbusLink? and also I should not test another terminator configuration before a certain time (1h?)?

My problem is that I have a lot of branches… for sure a loop… and I did not do the wiring myself, and I don’t have the plan… Does not sound good, right…

Have a nice day

Hello, I’ve been on a promotional event all day, so this is my first chance to look at my phone, for anything other than demonstrating a Velbus demo rig.

There are no hard and fast rules as to where the terminators have to be, or even how many (other than a minimum of 2).

Everyone has to play around a little to see what works best.

You could try removing the return leg and just run with a long cable run.

A loop is only a safety net in case part of the loop gets damaged.

In fact, the guidance states that a return section shouldn’t be added / connected until everything is working perfectly, just in case there is a loose / missing connection that wouldn’t be obvious in a closed loop.

(Which might well be the cause of an issue)

This is more specifically to do with terminating balanced lines, so the receiver components are presented with balanced voltages.

This article might help…

Now this bit I’m not totally clear on, maybe a Velbus tech can explain a bit better.

My understanding is that if a module can’t see a gap on the bus to transmit it’s message, it will wait for n ms and try again.

Then if it fails, wait for n2 ms.

If it fails again, n4 ms.

And so on.

So it’s quite possible for it to wait quite a while, but it will calm down.

And finally regarding the wiring plan, it’s not essential to know, I’m not entirely sure of my own Velbus cable route / layout these days, only because it’s not really a major issue.
Once the terminators are in the right time zone, the future will be protected from the rise of the machines.

Whoops, sorry I meant, once the terminators are in the right place, you should never have to think of them again.

Good luck,


You should know that checking the delay column in VelbusLink might not always be a good indicator; it is calculated on when the previous packet was received or sent.
The only reliable way to use this if your bus is quiet and you would send a single scan packet and measure the response from that.

The terminators should be as far between each other as possible distance wise (longest cable), but it isn’t an exact science.

As for the ‘module calm down’, it is based on the module’s address and only when there are bus errors. Generally you shouldn’t have to worry about that.

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Good evening and thank you both for your replies.

I’m still playing with the terminators.
It is now connecting in 25 minutes.

Could you please indicate me roughly what it is a normal connection time in the VelbusLink for an installation like mine? It is a relatively big installation I think, and maybe 25 minutes is normal?
I have :

Thank you


Just to be clear

Do you mean it takes 25 minutes to make the initial connection and complete the scan to see all the devices.

Or do you mean that it takes 25 minutes to connect, scan and read all the modules?

Either way, 25 minutes seems a long time.


It was 25 minutes to connect + scan. Not reading the modules (I work with my saved project).

I removed the return leg from my loop, it decreased to:

  • 20 minutes connecting with USB
  • 2 minutes connecting with the HomeCenter (with error messages that disappear by themselves)
    Is this normal to have such a difference?

Thank you

Even 2 minutes would be considered relatively long through USB.

By connecting do you mean VelbusLink is showing a window “Gathering statusses from modules” and you’re unable to do anything until the window is gone?

Yes, that’s it.
There is a popup window with the message that it’s gathering statusses from all modules.
And I’m not able to do anything until it’s completed.

There should be something wrong in the installation then…
Or do you still believe that moving the terminators elsewhere could solve this problem?

That would indicate that the bus is saturated and VelbusLink doesn’t get the opportunity to gather said statuses, and is why you’re also getting bus errors.

Some other pointers you can try:

Try measuring the voltage between + and - at your furthest point in the loop, this should be between 12 and 18 V.

With the power supply of the bus off, measure resistance between H and L, with 2 terminators this should be around 120 Ohms.

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If the bus would be saturated, wouldn’t I see it in the monitoring window? (the square on the top right of the screen, showing the activity on the bus).
In my case, the activity is low there…

I will do your tests tomorrow.

I was wondering… would it be possible that the problem is due to the cable used? Mostly EIB cable is used in my installation. But I noticed that in some places, 8-wire cables have been used… (smaller wires then), and 2 small wires have been used for one wire on the EIB cable.

The bus errors are causing the saturation on the bus, the modules aren’t getting their packets onto the bus, which is why you’re seeing no/low activity on the bus.

The mixing of cables shouldn’t be an issue, plenty of installations are done with FTP/UTP cables (where two wires are grouped together for one wire).

Just for clarity…

The majority of issues over here are caused by people thinking that it is okay to use solid core thin Cat5 or Cat6 style cables.

Technically, yes it is perfectly okay to use them, the issue seems to be that the rising cage clamps are tightened too much and the cable core fractures.

So for all the world the connection looks great, but with a gentle pull, the core just falls away to reveal the failed termination.


The core is put the wrong side of the rising cage and only held in place because it’s partner is secure.

So these days I make a big deal about using multi strand cable.