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How can I change a normally open switch to a normally closed. My Alarm panel needs NC and my boiler alarm is NO.

I want to attach my boiler to my alarm panel to an extra zone I have.  Problem is my alarm panel wants to see it NC until there's trouble and then wants to see it NO when it's tripped or in alarm.  My boiler alarms points are NO until the boiler goes into lock out and then it goes NC.  I would like to know if there is a way to add "something" so that i can monitor my boiler and know if it goes into alarm.  My boiler is a Weil Mcclain Ultra seris 3 with a U-control system if that helps.

just thinking about it a little, if youve enough capacity left on the AUX 12v terminals on your alarm panel, you could even use this to run your extra relay, and locate the extra relay inside the alarm panel to keep things neat with just one pair of wires (bell wire, flex, speaker wire, whatever) running to your boiler NO terminals

this would need a 12v double throw relay and also a diode in inverse parallel across the relay power connections to protect your alarm panel (the diode isnt necessary if you are using a battery pack)
easy enough... does your alarm system definitely use NC detection, or is it an "End of line" resistor system using a shunt and a tamper resistor in the detector?

either way, you just need an extra relay which has "double poles" (get a isolated DPDT type so you can use one set of poles to trigger the alarm system and keep the other set of poles for indicator LED or whatever), and a battery pack or mains transformer suitable for driving the relay
 
use the NO terminals on your boiler to act as an inline switch to turn on or off the extra relay, powered by the battery youve chosen

use the NC contacts on the extra relay to trigger the alarm panel

in theory, when your boiler goes into alarm its relay contacts will close, in turn switching on the extra relay.  this will make the NC poles on the extra relay go OPEN CIRCUIT, thus triggering the alarm system
the extra relay will only draw current from the battery/mains transformer when the boiler is in ALARM, so the majority of the time it will use no power at all

if your alarm panel is EOL type, it can get a little tricky as you will need to add the correct resistors to your relay setup, you should refer to the technical manual for your alarm panel, or if you are stuck let me know and i could draw up a rough diagram, im also a security systems engineer so im familiar with most alarm panels and detection so may be able to help with any other interfacing queries

hope this helps
kelseymh4 years ago
You can do that with a simple relay.

If you've got a "commercial" system, you could add either a DIN-rail or VME (depending on the complexity) alarm module with configurable NO/NC inputs and outputs, and both switch and monitor the boiler's state.  However, that gets (unnecessarily?) complicated.
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