Moving C-Bus Classic Switch

Hello

There's a guest room in our house with a C-Bus 4-way classic switch, however it's located a couple of meters into the room down a few steps. Not too long ago someone tried to find the light switch in the dark and didn't see the steps, had it been some of our more elderly relatives and it could have been a bit hairy!

I'm not sure why it was installed there in the first place, but I'd like to move it to just inside the door. It's not a problem to get access to the floor boards, as I assume that is where the cable must come in.

I've got a moderate knowledge of electronics/electrical work, so I was wondering if this is something that I would be able to attempt myself? Is moving a C-Bus switch something that would cause problems (we have no programming interface on the system for me to do any work to it if it fails - just dimmer units and light switches). Can I just pull the floorboards up, extend the cable and chase it up the wall to the new location, then re-wire the back of the switch and mount it?

I'd be happy to get someone in to do the work, but it's proving hard to find someone near Manchester (UK) that is familiar with C-Bus.

Cheers,
Ian

 

For what you want to do, it is pretty simple. C-Bus is Safety Extra Low Voltage, which means it's not immediately dangerous, but still worth being careful. To be safest, turn off the power, but if this is too difficult, you can work on C-Bus 'live' without fear of electric shock (assuming you aren't wringing wet and have a normal skin resistance). C-Bus key units can be 'hot plugged' without any fear of damage, and will recover load states within a few minutes (depending to some extent on the way they have been originally configured) without disturbing the load settings.

Assuming you can't just take up the slack in the existing wiring, there are a number of wires in cabling normally used for C-Bus, but key units use only two pairs of conductors in parallel to make two connections. For a short extension, you could splice all 8 conductors if cat5 cable was used or you could just use two strands of copper wire at least 0.5mm diameter to extend the two connections - replace the original switch with a pair of screw tunnel terminals (or equivalent) and if possible (but not absolutely necessary), retain a twist every few cm in the extension. Remenber to preserve the polarity (reversal will not cause any damage but the key unit simply won't work, and polarity reversal may cause a few other nearby units to temporarily stop working as well due to the increased network load).

In other words, you can do it. - if you mess up, it's really hard to cause permanent damage so you should be able to recover easily.
Make sure you make a good connection at the junction to the extension as intermittent connections are a real pain.

 

Thanks for the reply Don!

It should be easy enough to turn the C-Bus network off as we've got separate breakers for each dimmer.

Is there a site anywhere that shows a tutorial or photos of a C-Bus install? It would be really handy to see some pics of what to expect once I start pulling things out of walls .

 

I went to trace the cables, but it appears that the CAT5 cables enter the box from above, which makes it much harder for me to re-route the cables. It's a solid wall and I can't access the cables from above to pull them down at another location.

Instead, I could move the switch around 1m away round a corner, which would at least improve the situation.

Can I just run past what I'm about to do based on your advice and then you can let me know if it sounds sensible?

• Unscrew switch and mark wires to identify polarity
• Terminate both bundles of wires in a screw terminal
• Attach pair from a CAT5 cable to screw terminal (i.e. blue and striped blue)
• Channel horizontally around wall and corner for 1 meter at ~20mm depth
• Mount new 25mm pattress at new location and terminal each wire from twister pair to terminals (noting polarity)
• Fill channels and make good

As I'm not going to be replacing the switch with anything more fancy, I may as well just extend using a twister pair from CAT5 (which is 0.5mm core IIRC) - that would make it much easier. Should it be fine to fill directly over the cable within the channel rather then using conduit - this would reduce the channel depth. Does it sound ok to wrap the screw terminal in insulation tape and then fill in the old pattress, or would a blanking plate be better practice?

 

You can connect into the C-Bus network anywhere. You might be able to move the switch to where you really want it, and connect it back to another more accessible part of the network.

You can then just insulate and blank off the original position, or even replace it with some other C-Bus device like a temp sensor or PIR etc.

Rohan

 

Good to see installers not using the recommended cable for C-Bus installs

What you have proposed is how the motions sensors are connected. Using a terminal block to two untwisted wires. Give it a go, as stated you can really go wrong.

 

Hi Ian,

You said you have a moderate skill level in electrical sort of work. If you are expecting to stay in this house for a while, perhaps you could consider purchasing a C-Bus PCI programming interface (5500PCU) and then take control of your home's C-Bus network going forward?

For what you are suggesting you want to achieve, another possible solution (other than the light switch move/addition) is a 5753L occupancy sensor above the door that could bring the room light up to, say 20% (or full automatically) if someone walks into the door giving ample light to see the original switch and the steps? Only issue is that it needs to be programmed hence suggestion 1. Though you can use the simplistic 'learn mode' to program it, this may cause issues with the existing programming if it was originally done with C-Bus Toolkit. The sensor can connect to the C-Bus wherever there is a cable in the ceiling space, which is where your C-Bus cables seem to be running to.

Good Luck with whatever you choose to do.

Brad

 

Thank you all for the help .

Good to know that it's so easy to extend using a single twisted pair (even if not technically ideal).

Unfortunately there aren't any other switches nearby that would be easier to extend from, this particular room is in an awkward place which is why I guess there's silly switch positioning in the first place.

I did think about getting an occupancy sensor, but I'd still have to do loads of work to add that in, so may as well go for the simple option of moving the switch, which should give a good result.

In future I probably will get a programming interface, perhaps via a touch-screen with logic. I'll probably do that next year though, as it's relatively expensive and I've still got a couple of rooms to decorate.

I'm going to start work later on today all being well .

 

Keep in mind not all CBus touch screens can act as a PC interface.

 

I did a test this afternoon with some CAT5 cable, just extended the existing 2 cables as described above and it worked a treat . I've not chased it in to the wall though.

I had a think about Rohan said about connecting to the network from anywhere - although there are no switches nearby, I forgot about an occupancy sensor in the room directly below where I want the switch. I pulled up the floorboards and there are what I think are 2 x C-Bus cables leading to the sensor and they pass below where I want the switch.

If I moved the switch to come off this cable instead, how do I add it in? Do I cut one of the cables and then extend both cuts to run to the new switch (i.e. ring)?

 

You can just cut and make a T-join in one of the cables. C-bus is topology independent so it is a mix of daisycahining and start and anything in the middle.

Just as long as there are no loops.

Once connected no re-programming is required - it does not matter where the switch is on the networks, it has its address and will control the groups it has been programmed to control.

Another option that is a little more expensive is to use a battery operated wireless switch (have never seen one in the wild, only in a brochure). You will need a wireless gateway as well.

Mick

 

Thanks Mick, are there any T-Join adaptors available? If not, what would you recommend I use to do this - would I need to join all 8 wires individually?

A big thanks to you all for your help, I'm so pleased that places like this forum exist.

Cheers,
Ian

 

Loops are okay - I don't know how that myth got started in the first place as it never has been a technical limitation of C-Bus.

As long as the total cable length doesn't exceed approximately 1km, C-Bus works fine. Extending a few metres even if it's at the 1km point would make little difference.

You should be able to find a few examples of C-Bus installations here in the forums (with the search tool). What you propose sounds good. If you stay with your original plan, I suggest a blanking plate to keep the network accessible in case of vermin or future additions or whatever else may bring you back to looking at the terminations.

 

Thanks, I'm looking at some of the other installs on this forum right now .

Last question (perhaps )... is there any risk of exceeding load if I attach the switch to another network branch (spur from occupancy sensor, rather than moving existing connection)?

 

I would suggest for a lot of us this 'myth' came directly from Clipsal.. I certainly remember it from day 1 of cbus basic training..

Interesting you mention its no issue.. Will keep that in mind..

 

Yes, changing the point at which the unit is connected could result in pulling the voltage of the bus at that new point down too far for reliable operation. If you can measure the network voltage on all the units and find them all above 15V with the modified connection, the system will work reliably, but if you can't get to some units, there is always the possibility that one or more are out on the end of a long run and may have lower voltages than expected. Good luck!

As for the loops - I've verified that there is no issue with my home install. Working without a hitch for the last 7 years.

 

Thanks Don. If I measure as close to where I intend to connect and find that it's well above 15V, would that be a good indication that all is probably ok?

 

Glad you said that because I was sure I was told that as well in training. My training was in 1997 which means I don't remember a lot of what happened that far back (even last week can be difficult to remember).

 

probably, yes. Absolutely? You can't be sure unless you know the layout of the C-Bus wiring and positions of power supplies.

if you have a layout like this:

powersupply-----------------unit1----------------unit2---------newunit

you would be safe, but if you have something like:

powersupply--------newunit---unit1--unit2---...---unit55

'unit55' will have the lowest voltage and while you might have 15V at 'newunit', you might be below that minimum at 'unit55'.

I don't know anything about your installation so it's difficult to say. Voltage drops are due to cable resistance so if all runs are short, you're probably fine, but if a few units are in a shed 200 metres away from the house, you might want to confirm the voltage at the far ends.
There are a few software tools that can read network voltage from units, so if you have a PC interface or CNI (ethernet interface) on your network, you can check the voltage at all units quite quickly.

As for the loops - I have an early printed copy of some of the C-Bus training documents and they do indeed say "no loops" in bold text, so the myth was started a long, long time ago. I just don't know how it was started in the first place.

 

Cheers Don! I'll measure at the unit I'm looking at spurring from and hopefully it will give me some indication at least. May just wire up a test length and see how it works .