RE: HA without fallback-CBUS

["Neil Ball" <neilball@xxxxxxxxxxxxxxx>]

It is unusual to find electrical override switches on most modern control
systems - many for the overrides are done in software so if the controller
has failed these will not work anyway! It is relatively straight forward to
add in switches or relays on the output side if the circuit if required as
a
manual override. It's just as easy to do what Nigel suggests and simply
hard
wire the lights in the event of a dimmer failure until a replacement is
sourced. If you use a system such as C-bus then it would also be worth
installing MCB's on each output so that you have circuit isolation to
control the lights when you've bypassed the dimmer electronics.



Neil B.



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From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf Of
Nigel Giddings
Sent: 14 January 2006 09:20
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] HA without fallback-CBUS



Martin,

It is my understanding that C-Bus is used in many commercial
applications, including the new Wembley stadium...

I don't know of any instructions supplied by C-Bus or any other BMS
manufacturer which suggests that 'back-up' switches are required in case
of failure...

I am also not aware of any safety regulations for commercial buildings
which say that lighting must have mechanical switches, as opposed to
electronic ones, for safety reasons. Of course emergency lighting will
be part of the design but not linked into dimmer failure...

The MTBF (Mean Time Before Failure) of a C-Bus dimmer, I hope, probably
exceeds a standard wall mounted dimmer. A total failure of C-Bus is
unlikely to occur unless you rely on a single Bus power supply which I
would suggest is bad design. C-Bus relies on a distributed design.

I will have a number of self contained emergency lights (5) to cover
mains failure or MCB trip but I don't intend to have over-ride
mechanical switches. Worst case, your dimmer fails, you identify the
problem you hard wire the light on till a replacement dimmer is
installed...

I am also using a Midon Temp05/Homeseer system to operate my central
Heating in my existing house(the automation was retro-fitted) and I did
install changeover switches to enable the existing mechanical switches
to act as a back up, in 3 years I've never used them. I will use a
similar system in the new house, still being built, but will have a much
simpler override as the new house has 11 heating zones. I will probably
revert to a single centrally located mechanical thermostat in case of
computer failure...

HTH

Nigel

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