Re: HA without fallback-CBUS

[Neil Fuller <neil@xxxxxxxxxxxxxxxxx>]

Just a few thoughts . . . .

I think Martins suggestion of manual over ride switches for critical
circuits is an excellent idea. However, I wouldn't put the switches on
the wall (I don't think Martin was suggesting this anyway?).

Rather, I would put the switches on the panel the CBUS units are housed
in, assuming that they are reasonably accessible. By doing that, there
is minimal extra wiring and there would never be a situation where a
CBUS dimmer would be "back-fed"

I deal with BMS every day and Nigel is quite right that BMS
manufacturers do not recommend adding HOA switches to over-ride their
equipment. That would be tantamount to the manufacturer admitting that
their equipment is less than perfect and may, one day, break down ;-)

However, I seldom come across an HVAC MCC panel that is not equipped
with HOA switches, which are normally specced by the consultant. Whilst
retrofit lighting systems will often be without HOA switches, I have
seen many new installs that do have over ride switches for fittings at
key locations. Largely it seems to depend on the  installed
infrastructure. If the dimmers etc are centrally located, over ride
switches are easy to provide. If however the controllers are
distributed, and above ceilings, it's rare to see  HOA switches.

Of course, emergency fittings will overcome mains failures etc and need
to be sited to provide illumination of key escape routes. Nigel, have
you installed a centralised emergency lighting system or used separate
luminaires? In my experience, the centralised systems , with their far
more reliable lead-acid battery stacks are much preferred over the
distributed systems, although of course the wiring has to be in pyro and
so starts to get costly (and I guess a large stack of batteries is
overkill for an average house).

Regards

Neil

Nigel Giddings wrote:

>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
>
>-----Original Message-----
>From: Martin McCreesh [mailto:martin@xxxxxxx]
>Sent: 13 January 2006 21:48
>To: ukha_d@xxxxxxx
>Subject: Re: [ukha_d] HA without fallback-CBUS
>
>I've been looking a half way approach for a cbus install later this
>year. Planning to put override switches for main lights at 2 key
>locations in the house. These locations will be CBUS nodes anyway.  One
>issue that maybe somebody can help with is what happens if you apply
>full power to a cbus dimmed circuit - could it damage the CBUS dimmer.
>The alternative requires a good bit of extra cabling and invloves using
>a two way switch to isolate the feed to the light from CBUS.
>
>  ----- Original Message -----
>  From: David Gumbrell
>  To: ukha_d@xxxxxxx
>  Sent: Friday, January 13, 2006 8:28 PM
>  Subject: Re: [ukha_d] HA without fallback
>
>
>  Depends what you mean by a fallback. My Idratek
>
>install<http://www.automatedhome.co.uk/modules.php?name=Forums&file=view
>topic&t=746>is
>  designed to be i) removable in case of sale and ii) tolerant to
>  control
>  computer failure due to Reflex (built-in) functionality. If there's
no
>power
>  to the HA network, there's probably nothing to switch !
>
>  I know of another Idratek install which has put the panel relays in
>parallel
>  with existing switching, which might be the kind of fallback you were
>  thinking of. I guess that you could do something similar with the
>other
>  systems (C-Bus etc) out there.
>
>  But really, anyone would think you can't trust this technology stuff
>.... :-)
>
>  Dave
>
>
>  On 1/8/06, Mal Lansell <mal@xxxxxxx> wrote:
>  >
>  > I thought most people did go the whole hog - wiring for
mechanical
>  > switches and for HA is mutually exclusive in most situations.
>  >
>  > So, wire it up, and buy a torch ;-)
>  >
>  > Mal
>  >
>  >
>  > Chris Hunter wrote:
>  >
>  > >'wondered if anyone had been brave enough to go for HA
without teh
>  > >fallback - ie: without manual switches on the lighting
circuits,
>without
>  > >manual timeclocks & thermostats, and so-on ... might
save a good
>part of
>  > >the costto go the whole hog ! ... less wiring included ... ?
>  > >
>  > >Chris
>  > >
>
>
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>------oooo0oooo-------
>14/1/2006
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