Electromagnetic noise in C-BUS 2-wire communications?

Hello guys!

Wasn't able to search out here for such a problem, which was happened recently in my client's house. Client reported me about problems with C-Bus system few days ago, and when I visit the house (late evening) I researched that some of wired keypad had to be readdressed (so they at least loosed their addresses in C-Bus bus). I correct it, but on next day client reported me about the same issue. After some researches I found out that problem with communications between keypads and din modules happens when workers in his garden use perforator. And when it happens I wasn't able to discover any devices in that system. So, question is - how such equipment as AC perforators could cause any kind of electric noise in DC based C-Bus wiring? And how can I get this solved?

Thanks!

 

Hi Yecora,

The noise sounds like it is induced rather than conferred through the power supplies though you might want an AC line conditioner on the C-Bus power supplies if this sort of noise is a common occurrence on their power eg. a farm / industrial etc.

As it sounds like the noise is induced, the C-Bus cabling requirements suggest that you check that all C-Bus pink cable is at least 150mm when run parallel to main cables, and where it crosses mains cable, make it at 90 degrees and make a loop over the mains cable of at least 60mm.

Another one to check is that all the pink cables have been terminated with correct colour codes used. It has to be terminated Orange/Blue as C-Bus Positive and OrangeWhite/BlueWhite as C-Bus Negative.

If another colour combination is used, the twists in the conductors down the UTP cable may not be properly contributing to the line noise reduction. A differential system is used whereby any external noise simultaneously induced into the positive cable of a pair and the negative cable of a pair is screened out at the bus control chip on the module, probably using a differential amplifier, much like how noise cancelling headphones work. Many older site were wired with a varied mix of termination and if correct 'pairing' isn't in place, noise immunity is reduced significantly.

Also check cable terminations on switchplate modules for a broken single strand near the terminations (which can happen quite often with solid core UTP if the switch has been on and off a few times for painting etc) where only one of the two conductors is actually making the C-Bus circuit rather than two. The broken cable acts like a long wire RF receiver and is more susceptible to induced noise and AC waveforms, which would effect the module at the opposite end from the break.

Hope this help and you find your bug,

Brad