Noisy dimmers vs poor electrics / earth

Hi Everyone

I'm in the final stages of a biggish Cbus project and I'm having trouble with some noise emanating from the dimmers. Briefly the entire system comprises 6 X 8 ch dimmers (1a) and 4 x 12ch relays (10a). All these housed in a Hager Board with MCB's on the dimmers returns. My AV system is housed in a separate server room in a 19" rack and has a Vantage Axium 452AV controller amp, Adcom 6006 amplifier, Sat decoder, tuner, PC for WMP via Vantage WTP. CCTV camera's are analogue via the Elan Z880 8x8 matrix and a quad splitter for the surplus - all video in / out is via the Axium controller (which I've never ever had any hassles with - really nice controller).

So here's the thing. The moment I dim more than about 3 loads I get anomalies on the video pictures around the house. The 'interference' is a trailing hum bar north to south and naturally the more loads I dim, the worse it gets. I'm using a Gepco dig video cable btw - really well insulated with a good dielectric and shield - also the AV runs are very separate in trunks and conduits.

I'm meeting with the electrician tomorrow and I'm going to ask him to perform an earth impedance test and check ranges. He mentioned that during the inspection they measured up to >20 - 30 v drop when loads were on. This means my rack gear is running at about 200 - 208v...???

Anyway I'm also going to try a Kramer Tools ground loop isolator tomorrow, but even if it sorts out the problems I'm a little uneasy about the situation and a possible ground loop. In my own house and other projects the CBUS dimmers run fine without causing any interference so I'm really relying on your combined experience here to help me out with some suggestions or anything I may have over looked.

Looking forward to your input.

Regards


Richard

 

I had a situation some years ago in a similar sounding install. Turns out the electrician had a bad connection (oops forgot type bad) on a main neutral on a sub board.

Get the sparkie to double check his neutral and MEN bond points in his board(s).

 

You can check the Type and Number of Transformers used in one channel of the Dimmer.

If you are using Electronic transformers, as you know, give some capacitive loading to the dimmer channel. And if the number of transformers exceeds the limit, you will have greater Electromagnetic emission. this will cause interference with the Audio and video signals.

this may be one of the reasons...

Give the details of the Type of Dimmer / Transformer, the Number of transformers used, the load etc...Great people around here who can help u in this regard.

 

Thanks for that guys!

Since posting I checked the overall earth integrity and as I suspected it was dodgy to say the least. We now have the kitchen LCD working beautifully after strapping the earths on close by plug points and under 30+ dimming loads all set to about 40% problem solved in theory anyway - all I have to do now is get the electrician back to clean up the rest of the install. Also, (and thanks Lucky) I found that all the neautral returns in my Hager board were inserted into the strips but the screws were not tightened (!!!)

From now on I'm going to insist on a separate board for all AV with built in protection and isolation.

Thanks again!

Richard