What can trigger an electric fence alarm, and why it keeps going off

A monitored electric fence raises the alarm for a handful of reasons:

1. The fence voltage drops below the alarm level. Something is touching the wires, a wire is cut or broken, or the fence is leaking current through plants or failed insulators.
2. A gate stays open too long. Gates wired to the energiser have an entry delay; leave one open past it and the alarm sounds.
3. The earth loop breaks. Where earth loop monitoring is used, a cut earth wire raises the alarm too.
4. Someone opens the energiser. A tamper alarm.
5. A service condition, such as a low battery after a long power cut. On Nemtek's Wizord, that sounds the buzzer only, not the siren.

Most "false" alarms are the first one, and they're not false: the fence really did lose voltage, usually because of something growing or moving on it.

Before silencing anything, look at the energiser or keypad: it shows which alarm it was.

• Nemtek Wizord: a flashing light means the condition is still there; a steady light means it happened and has since cleared. The fence light flashes when the fence voltage isn't good enough, and the gate light when a gate is still open. Its buzzer also sounds differently for a fence alarm and a gate alarm.
• Nemtek Druid LCD: x means the fence voltage is below the alarm level, o a gate is open, and t the cover is, or was, opened.
• JVA Z-series: count the status light's flashes; one means a tamper.

Write down what you see. It tells a technician most of what they need, and it's the difference between "the alarm keeps going off" and "the fence alarm, every night after the wind picks up".

On a Nemtek Wizord, switching the energiser off with its Nemtek tab or a remote key-switch silences the siren, the buzzer and the strobe. It beeps once when switched on and twice when switched off. Then:

• If the alarm light is steady, the fault has gone: switching the energiser back on clears it.
• If it's still flashing, the fault is still there, and the alarm will come back until the cause is fixed.
• To clear the memory, Nemtek's sequence is on, off and on again.

On keypad-armed energisers such as Nemtek's Druid and JVA's Z-series, disarming with your code does the same job. Don't disconnect the siren or the battery to stop the noise: it leaves the property with no alarm at all.

Nemtek's advice is to keep the fence clear of vegetation and check it now and then for slack strands. Those two cover most repeat alarms:

• Plants and branches that touch the wires, especially in wind or after rain, when they're wet.
• Slack or broken strands that sag onto a bracket or the wire below.
• Cracked or dirty insulators, which leak current, most of all when wet.
• Something thrown or blown onto the fence: a branch, a plastic bag, a wire coat-hanger.

Look along the fence from a safe distance, without touching it, and note where you see anything. Clearing the fence is done with it switched off, and replacing insulators or re-tensioning wires is a job for us. Our guide to an electric fence that isn't working covers a fence that's weak rather than alarming.

Gate alarms come from the contact on a gate that's wired into the fence. On a Nemtek Wizord, the entry delay can be four minutes, one minute on the Wizord 2, or none at all; leave the gate open longer, and the alarm sounds. JVA's gate input works the same way, and while the fence is disarmed it can simply chime when the gate opens.

So a gate alarm usually means the gate was left open, didn't close fully, or its contact has moved out of line. Close the gate properly; if the alarm persists with the gate shut, the contact needs adjusting.

On mains failure, a Wizord drops its output to save the battery, and Nemtek notes the fence display may not be fully lit, so restore the mains before judging the fence. A long outage can also run the battery low and light the service light. With a good battery, Nemtek gives the Wizord about 24 hours without mains, and it asks for batteries to be checked twice a year. If a service warning stays after the power's back and the energiser has been switched off and on, call us.

Energisers let the installer decide how sensitive the alarm is. Nemtek's Druid LCD, for example, can be set to need from 1 to 15 failing pulses in a row before it alarms, with 3 from the factory. A sensible setting helps on a fence that sees the odd brief disturbance. But turning the sensitivity right down to stop alarms just means the fence no longer reports a real cut or a real climber. We find and fix the cause first, and only then look at the settings.

An alarm that never sounds can be worse than one that sounds too often. Check that the energiser isn't set to silent alarm (a Druid shows s), and that the siren and strobe work. The proper test is the one JVA prints: open a join in the fence to simulate a break, and short the live wires, and the alarm must go off each time, on every zone. That's a test for us to do, and you can read how it works on our Saxonworld fence page.

Call us when the alarm keeps returning after you've cleared what you can see, when a tamper shows that nobody can explain, when a wire is broken, or when the siren never sounds. All our spare parts are genuine, and every repair comes with our six-month guarantee on our repairs. More on fences is on electric fence repairs.

On the job card, give the energiser's make, which light or symbol shows, and when the alarm happens: at night, in wind, in rain, or after a power cut. Same-day repairs are offered when the day allows. No call-out fee when we do the work. If no work is done, a R650 call-out fee applies.