After it rains CBus shuts down

Our seven year old CBus system either shuts down or causes lights and blinds to go haywire while it rains. The electrician has investigated many times but can’t find what’s causing the problem. We seem to be paying for trouble shooting without a solution. Although there is power to the fuse box, there is no power to the switches. It’s a new house with no leaks. Any advice is welcome. We are based in Sydney Australia

 

Hi Matt,

An interesting problem to diagnose. I note that the C-Bus network is down as the C-Bus lights are all off on all the modules. This is usually due to:

1. Insufficient C-Bus power on the C-Bus network for the number of devices or faulty / noisy power supply
2. a short circuit on the C-Bus cable network
3. no detectable C-Bus clock

Some more information will help.

Are there any outbuildings or outside services on the C-Bus, like pool plant room etc? C-Bus Pink cable underground in conduits can fill up with water and oxidise.

Do you have any outdoor Passive infrared movement sensor on C-Bus? These can fill up with water in rainy conditions and bring down the C-Bus network.

How many C-Bus light switches, blinds under C-Bus control and occupancy sensors? Is this board the only one?

Where are you located? Near water, the beach / harbour etc?

Brad

 

Hi Brad

thanks for this. We are close to the Harbour have external garden lights, outdoor sensors on the CBus network. Maybe one of these could be the culprit. Since posting the rain has stopped, skies have cleared and the CBus is back on has consistently been the case. The issue never happens when the sun shines. We have three boards approx 35 light switches 14 blinds. Two external lights with sensors. I’m guessing because the CBus always comes back on soon after the rain stops the issue is in an area where water dissipates quick quickly. mom not an electrician but wouldn’t the system trip if affected by water?

 

The most likely cause of this sort of thing is water getting into a cbus (pink cable) connection somewhere. It only take a drop or two to upset the bus and stop communication. It won't trip anything as the bus is low voltage and short circuit protected. The cable also has global remote on and remote off lines which are never used in a domestic install but tiny amounts of water can cause either or both to be triggered and give the symptoms you are experiencing. If you can reproduce the problem you can split the network to isolate the problem, otherwise it's just a case or following the bus along and checking all connections. Start in the roof and any external units.

 

Hi Matt,

The reason I asked about your location is that many of my clients are on Sydney harbour or a beach front and going along the same thought lines as Ashley's suggestion (which I completely agree with), I also quite often find at about 4-7 years of install life, the RJ-45 pink cables between the C-Bus modules in the electrical board can get a high resistance connection on the RJ45 pin slide in the RJ45 socket due to pin/slide oxidation pitting. Something (for your sparky) to do here is run each pink RJ45 cable connector in and out of the socket on the module 4 or 5 times so it makes a new clean low resistance connection. I've seen this same issue happen on POE cameras out in the salt air with RJ45 sockets as well.

I've seen that 'rarely' the Clipsal 5750WPL PIR sensor when it gets pretty old can sometimes end up getting water inside the PIR head in strong pressurised rain / strong harbour breeze with driving rain scenarios. The PIR base can also sometimes fill completely with water if wall mounted and then depending where the C-Bus terminal block connection has been placed, the cable into the head unit can wick some water through with the daily heating / cooling pressurisation/depressurisation of the PIR head. They usually work again after drying out in the sun, but can pull the C-Bus network voltage down when it rains heavily for a few days.

You are best to diagnose this issue when it's down, not afterwards when it's up. Get your sparky to run a diag or search for the issue when it's raining and flaky.

At a basic level, the C-Bus power supply required to run your network is:
Outside PIRs x 2- 18ma x 2 = 36ma
35 x C-Bus light switches x 35 = 35 x 22ma = 770ma
14 x C-Bus blind/shutter relays= 14 x 22ma = 308ma
2 x Aux Modules (2 sighted in your images - any more?) 2 x 18ma = 36ma
Anything else? Inside occupancy sensors? Touch Screens? PC Interface modules? Alarm C-Bus modules? -

If not, required power supply is at least 1150ma so you need at absolute minimum 6 x C-Bus dimmer / relay modules with the inbuilt 200ma power supply (but more like 8). Do you have this?

It is written on the front of the dimmers and relays eg. '200ma inbuilt C-Bus power supply included'. The network also needs at least one (but preferably a few-standby) stable C-Bus clock and one burden. Your sparky needs to check this.

The best path forward is onsite diagnosis during a failure. If you or your sparky needs a hand with that, give me a PM / call.

Brad

• www.noushouse.com.au

 

I had a similar issue when my sparky hadn't properly terminated and insulated my cable run for a retracting roof prior to the roof installation.

I was lucky that it was obviously the cause as the wire was hanging out of the wall 12 ft in the air.........

I made him go insulate it in the rain, as I expect more at the rates I pay them.

I would start with outdoor PIRs and any units against outside walls, the issue is unlikely to be mid cable run as the cable is double insulated, its more likely a bare end or at an input unit.