RE: C-bus Channel won't turn off...

["Keith Doxey" <ukha@xxxxxxxxxxx>]

Hi Rob

> My system was installed around the same time as the big debate
> was going on
> and unfortunately I didn't read about the issue until after mine
> was almost
> finished. I have a single MCB covering one enclosure with 3 x 8
channel
> dimmers.

With just one MCB for 24 channels I am guessing that it is rated at 10 amps
or greater. The triacs are probably only 8A devices so dont stand much of a
chance. Your MCB is there to protect the wiring from overload in the event
of a fault. It is not sensitive enough to protect a tiny little triac as
you
have found out. The momentary surge when a lamp blows can be many tens of
amps or even greater which is why it will often take out a much higher
rated
breaker.

Can you add another enclosure to fit some individual Low Rating MCB's in.

Alternatively, a plastic box with panel mounted fuseholders and HiSpeed
Ceramic fuses.

My old disco lighting controller had internal quick blow fuses rated at 2A
which were a pain to replace as I had to turn the power off and remove the
lid.

I replaced the internal fuses with 5A and put 2A fuses on the rear panel
which was much better but I still occasionally got triacs being blown, on
one occasion a lamp took out the 5A fuse and the Triac but the 2A survived
:-(

I then uprated the 8A triacs to 16A versions and replaced the quick blow
fuses with HiSpeed Ceramic. This then gave me the protection I needed and I
NEVER lost a triac again despite on one occasion blowing 8 fuses in quick
succession whilst trying to identify which lighting lead was faulty!

> I've had three halogen bulbs blow before on the same channel without
any
> damage. The mcb usually goes but that's all. Most of my lights are LV
> downlighers which, touch wood, I've had no blown bulbs with.
>

The surges from those failures may have weakened the triac and the latest
one was the final straw. It also depends greatly on where in the mains
cycle
the bulb blows. At the peak of the mains cycle the current would be the
greatest.


> In the dinning room and kitchen I have some temporary mains voltage
light
> fittings, the type with a long bar and adjustable fittings, that
> blown quite frequently, Usually when the children are jumping around
in
the
> room above.
> Could it be a dodgy fitting or are halogens very susceptible to
vibration
> damage? The lights do vibrate significantly when the children are at
work
> above!
>

Bulbs are more susceptible to damage from vibration when cold as the
filaments are more brittle. I rarely had bulbs fail whilst doing a disco
despite them being flashed on and off repeatedly, but would often find that
although all lights were working when I finished, there would be some bulbs
gone the next time I set up. (More so if my mate had transported the gear!)

> Would LV halogens be less likely to cause damage to the channel as the
> transformer has some sort of short circuit protection? Does the
protection
> cut off all current on the channel or does it just protect the
internal
> circuits of the transformer?

Depends on the transformer.

Regards

Keith