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

["Keith Doxey" <ukha@xxxxxxxxxxx>]

Hi Robert,

> I had a downlighter blow this evening which tripped the mcb that
> covers the whole 8 channel dimmers. After resetting the mcb all
> channels are ok except the one that blow,
> It's on but I can't turn it off.
>
> The led on the switch goes on and off, and I can see the network
> messages in the C-Gate window, but the actually lights don't respond.
>

Classic symptoms of a blown triac :-(

Triacs normally fail Short Circuit so that the load is permanently
powered.*

Lutron also have a relay in their dimmers that physically disconnects the
load when OFF. This means that in the event of a blown triac, you still
have
basic ON/OFF control of a load. Having said that, Lutron use such over
specced triacs that it is virtually impossible to blow one!

Do you have individual MCB's on each channel or just a Master MCB ?

Low value MCB's on each channel, or a low value Ultra Fast fuse on each
channel is the best way to protect a dimmer. IF you had individual MCB's
then it might have tripped fast enough to protect the triac although there
is no guarantee of that, but at least you would be able to turn that
channel
OFF by flicking the breaker off.

Above is general advise regarding dimmers as I dont actually have CBus but
have fixed lots of blown triacs.

Regards

Keith

* One lighting controller I repaired had failed "open
circuit"..... al least
I'm pretty sure it did because all that was left of the triac was three
legs
sticking out of the PCB and a blast mark on the inside of the case!!!!