Find a low-voltage relay that has a normally-closed pair of contacts.
Use a transformer or battery to power the relay using the fence as a conductor. The normally-closed contacts will be open when power is present. When the fence is cut, they will close.
Use them to switch the siren, light, or whatever.
Hi,
Is there a simple print layout or electr scheme for the following purpose :
I have a fence with three barbed wires. I want a light and a siren to go off when they're cut. Siren runs on 220VAC, light also.
Thanks for any reactions! Erwin Maes
:
Assuming that the tree barbed wires are running together, run the three barbed wires in series (insulate from the ground and fence supports) by joining two of them at the far end (say, top and middle ones). Join the middle and bottom wires at your end, then bring the far-end of the bottom wire back with an extra cable. You now have what is essentially one long run of barbed wire (plus the extra bit to bring back the remote end). Get yourself a 12V wall-wart (AC or DC output, no problem, just match it to the siren relay). [Use 24V if it's a really long fence]. One end of the wall-wart output connects to the fence, the other end to the relay coil. The other relay coil connection goes to the other wire from the fence. Use a siren with an in-built relay controlled by an external relay contact closure so you're not screwing around with your mains (that relay contact will obviously be the relay connected to the fence). If this seems unclear, get an electrician to wire it for you.
Ken
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