Re: PIRs & Sensors dual wiring

["PatrickLidstone" <patrickl@xxxxxxx>]

--- In ukha_d@y..., "Mick Furlong" <hiltoneltd@y...>
wrote:
> Simon
> 
> I am thinking of having a pretty standard monitored alarm system 
and rather
> than try and make it pass events to a PC or HV I was hoping the 
signals
> could be split at source.
> 
> What exactly are the issues with doing this via a single relay?

As I think you know, Mick, I did exactly what you described in my 
previous house. *But* my alarm was not monitored. In my case, I 
simply used a PC digital IO board interface in parallel with the 
switched output from each sensor, terminated at the alarm panel. It 
worked a treat.

Monitored alarm systems place an emphasis on reliable installation. 
Any direct connection to the PIR output's could hypothetically be 
used to disable/bypass the alarm panel. It's also possible that a 
poorly installed/designed interface could induce false alarms in the 
control panel. These issues can be avoided by electially isolating 
the alarm panel, PIRs and computer interface - through the use of a 
double pole relay. I suspect that a Nacoss installer would insist on 
this approach - and Nacoss approval is a pre-requisite of being 
connected to a monitoring service, at least in the UK. (Perhaps with 
the exception of Intamacs service?). 

Patrick



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