Operating distance for a VMB4RYLD

I currently have a cabinet with several Din rail mounted modules.

However i have a pond that i intend to automate and plan to do this by putting a VMB4RYLD unit at the pond to use one incomming mains power supply across several pumps and filters.

The pond is about 50m away from the main velbus panel so i have two questions.

I assume the bus wiring is ok over that distance ?

Do i need to provide a local 12v power supply unit for the relay or can the 4 wire cable i run that contains the two for the bus allow the unit to operate over that distance allowing for any voltage drop. In other words, what is the max distance the VMB4RYLD can be from the 12v and still operate ?



That sounds like a perfectly good idea.

The maximum cable length depends on the type of cable you use.

I completed an installation last week with something similar to what you are suggesting.
There is an outbuilding at the end of the clients garden which has a length of armoured mains cable and a single length of external grade FTP Cat5e for the Velbus network.

Currently they only have a VMBPIROB connected, so I didn’t bother giving it a seperate power supply.

I believe that the FTP Cat5e cable run is at least 40 metres.

According to a conversation with the product manager at Velbus (some years ago)…

A good Cat5e cable should be able to service Velbus nodes up to 1Km from first to last module.

A high quality DeviceNet cable should be able to service Velbus nodes up to 3Km from first to last module.

This is a massive advantage over other automation technologies :slight_smile:

There is more detail about this in the new 2 part installation guide, which I think shows examples of cables.

Good luck automating your water feature.

Please post a comment (and picture) on this topic, as I’m very keen to show the world just how adaptable Velbus can be.


Thanks MDAR

So do you think if i ran a large enough 4 core (2 cores for power) cable (to avoid voltage drop) from my main control cabinet i could power the relay from the same powersupply without having to add an additional power supply local to the relay ?


No problem at all :slight_smile:

Where a customer doesn’t want to run DeviceNet cable or EIB cables, I adopt the following wiring plan.

Cat5e style cables, preferably stranded cores.

Blue / White & White Blue = Power 0V
Brown / White & White Brown = Power +
Orange / White = Data High
White / Orange = Data Low

You are right in suggesting that the CSA of the cable is important to reduce volt drop, so using two cores will be plenty to run a couple of relays / modules without a local power supply.

Just as important is to maintain a twist in the data pair to prevent spurious data events caused by EMI.

Officially I’d recommend a good quality EIB cable, but in reality a good external grade Cat5 FTP will be more than adequate.

Good luck.

Thanks MDAR, will post more when i get it going.

One more question you can maybe clear up for me.
I know the bus cable has to pass through each unit, thats clear.
I also know about the terminal jumpers.

However, if i already have two terminal points, i.e. the USB connection and a glass panel switch, and i want to run two relay units out to the pond area, do i have to run the bus out to these two units and then back again so the bus is effectivly one long line, or can i run a branch of and have effectivly three terminal points.

What did you do on the out building project ?


Hello Andrew,

With over 8 years of working with Velbus, I’d like to think you’ve got a good grasp of it :wink:

Although a loop is a good idea, it’s perfectly possible to run long radials.

Or a loop, with a radial.

Or multiple radial runs from a central point (star style)

As for terminators, I’ve fitted as few as 1 in a system but never more than 3.

It really all depends on how your system behaves.

You might find that you only need your existing termination.

Or you might find that you need 1 in your cabinet and one on the new long leg / radial.

Or you might need 1 in your cabinet, 1 somewhere near the mid point of your loop and 1 on the long leg.

For reference, the bigger job I oversaw last week we ended up with 2 large loops and 4 short radials and 1 long radial to the outbuilding.

We put 1 terminator in the main cabinet, 1 in the mid point of the shortest loop and 1 in the outbuilding.

This combination was the first we tried and it suppressed the data line reflections effectively, we didn’t bother trying any other combinations.

I hope that help.

Good luck,



Hello Andrew

Did you get my email regarding the 2 relays?