Discuss 24v Fire Alarm Needs to Switch 240v shut off valve/Solenoid in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
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Hopefully a diagram might help any 24v coiled relay with mains rated 10A contacts will do the job,
As engineer54 mentioned a relay is the way, very straight forward, you want a 240 volt relay with a 24 volt dc coil, when the bells ring the relay coil is energised and the supply to the gas valve is broken, how you energise the coil is a matter of a couple of ways, via an alarm relay in the panel or by a sounder itself, the latter not so good as you may need a diode doing it this way to ensure the panel doesnt go into fault.
This suggested set-up isn't fail safe assuming the alarm is acting on a real fire situation then as soon as this cable looses supply and/or is damaged by fire the solenoid will open again letting gas through, although im unsure of codes of practices here i feel its not as simple as it sounds, if op has a output relay then volts free then an external power supply with independant battery back-up should be holding the relay open and the failure of the independant supply or alarm activation will close the valve ... any fire damage or general damage to the cable will then see the valve close.
Its possible dependant on the alarm panel to use the internal 24v supply to eliminate the need for a external relay and power source but this will be dependant on the size of the solenoid and the 24v output max current rating.
As already mentioned it may be the case that safety relays or specific interface boards should be used and another issue is the reset and indication system the gas valve shouldn't re-energise automatically IMHO without a operator reset been applied but il reserve this judgement for now as resetting the panel could be classed as a operator reset, also a test function should be implemented into the design and if done and an over-ride as you dont want to loose the gas and have to prime all the boilers and burners everytime you do a test on the alarm although it should be subject to its own testing routine.
Reply to 24v Fire Alarm Needs to Switch 240v shut off valve/Solenoid in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
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