Electric fence energizer repairs, replacements and how to choose one

An energiser sends short, high-voltage pulses out along the fence's live wires and measures what comes back on the return. While the voltage holds, the fence is armed and quiet. When a wire is cut, shorted to the bracket or pulled to earth, the returning voltage drops below the alarm level your installer set, and the energiser sounds the siren, flashes the strobe and tells the alarm panel.

Around that job it does a few others:

• Runs on a battery, kept charged from the mains, so the fence stays live in a power cut.
• Watches the gates through magnetic switches; Nemtek's Druid keeps watching them even with the fence switched off.
• Fights arcing. Nemtek's Druid LCD energisers sense a wet, dirty or cracked insulator arcing and run the fence just below that voltage, keeping more energy on it than a conventional energiser would.
• Reports its own health. A display or keypad shows the fence's condition, alarms that happened while you were out, mains failures and tampering.

Two numbers decide which energiser a fence needs:

• Joules are the energy in each pulse. More joules hold the voltage up on a longer fence, or one with more lines and more leakage through plants and insulators.
• Zones are separate stretches of fence, each with its own alarm. A single-zone energiser treats the whole boundary as one; a two-zone model tells you which half to check.

The biggest isn't automatically the best. We size the energiser to the fence's length, lines and zones, and every one must be a type tested to IEC 60335-2-76, the standard Nemtek's and JVA's manuals both cite. The Druid 25 and 28 can be linked as master and slave to make a four-zone system, the simplest way to split a long perimeter without starting again.

• Nothing on the display with the mains on, or it won't switch on from the keypad or tab.
• Alarms with nothing wrong: the fence is clear and the insulators clean, but it keeps alarming. (Check the fence first, though: plants and dirty insulators cause these too.)
• Low voltage on a clean fence, a condition score that won't climb after the fence has been cleared.
• Battery warnings that don't go away after the mains is back: the battery isn't charging, or it's worn out.
• A service symbol that stays on a Nemtek Druid's display, or a t that says the cover is or was opened.
• After a storm or a surge, any of the above at once, or a burnt smell from the box.

If the fence itself is the problem, start with electric fence not working.

Most "resets" are really one of three things:

1. Silencing an alarm. On a Nemtek Druid LCD, hold the Nemtek tab over its logo on the front: a short beep, then keep holding until a longer beep. The siren, the beeper and the strobe stop.
2. Clearing the history. A symbol for an alarm that's over clears when you switch the energiser off and on, or hold the tab to the long beep. An alarm that's still active won't clear until the fault on the fence is fixed.
3. Using the keypad. The master PIN (1234 from the factory) switches the fence on and off. The reset PIN (5555 from the factory) can silence and clear alarms but can't switch the fence off or change settings. Change both defaults: anyone who knows them can switch your fence off.

A factory reset puts every setting and PIN back to Nemtek's defaults. It needs the energiser's mains and battery disconnected inside the box, then a code entered within a minute of powering up, so it's a job for us: the box works at a lethal voltage and must not be opened by anyone else.

Nemtek's Druid LCD energisers run on a 12 V 7 Ah sealed lead-acid battery, kept charged from the mains. Nemtek says a new, fully charged one typically gives more than 24 hours on a Druid LCD, less on a fence in poor condition. Two rules from the manuals: never fit a non-rechargeable battery, and keep the energiser somewhere ventilated, because a lead-acid battery can vent gas while it charges.

If the battery runs completely flat in a long outage, a Druid keeps its settings and comes back as it was once the mains returns. A battery that keeps going flat sooner than it used to is worn: a new one is R230–R450 (Takealot) in shops. The energiser also needs a plug point close by; a new one is a job for a registered electrician.

An energiser has more connections than it looks, and getting them wrong leaves a fence that alarms, doesn't alarm, or isn't safe. In outline:

• Fence out and return, for each zone, in high-voltage insulated cable, never sharing a conduit or hole with low-voltage wiring.
• Earth, to a main earth spike as close to the energiser as possible and at least 10 m from any other earth system.
• Gate switches, wired so the switch opens when the gate opens, on a cable up to 100 m long that doesn't run alongside the fence wires.
• Siren and strobe, and the keypad, on Nemtek's keypad bus of up to 100 m.
• The alarm panel, through an isolation relay, never powered from the energiser's battery.

These come from Nemtek's installer notes, and they're why connection is an installer's job: it's live at high voltage and has to meet the fence standard. How a whole fence goes in is on electric fence installation.

An energiser hit by lightning or a surge, or one with water inside, is opened on the bench and either repaired or written off. We tell you which before any work starts. Typical market prices, not ours:

A new energiser is matched to the fence and set up with its alarm levels, zones, gate inputs and keypad, and comes with the maker's own manufacturer's warranty. All our spare parts are genuine. Six-month guarantee on our repairs. Prices checked October 2026. Your exact price is set in a free quote before any work starts. No call-out fee when we do the work. If no work is done, a R650 call-out fee applies.

Security energisers on homes and businesses run from the mains and keep their own battery charged. Where there's no mains at the energiser, Nemtek's Merlin installer notes allow it to run from an external battery instead, with a jumper set inside so it powers up, the correct polarity, and the battery kept below 14 V. Keeping that battery charged, by solar or otherwise, is a design question for the site, so ask us before buying a solar or portable unit, to be sure it suits a security fence.