Repair defective boundary wire

The boundary wire completely surrounds the lawn. It begins and ends at the charging station from which an electrical impulse is sent out. This signal tells the robotic lawnmower where the boundary of the lawn is. In the event of a defect in the cable, the signal is interrupted, the robotic lawnmower then stops working and issues an error message until the fault is corrected. The good news is that you do not need to replace the entire cable, but you can repair a defective boundary wire.

Causes of a broken boundary wire

There are many reasons for a broken wire. In case of an above-ground installation, it’s normally the result of the robotic lawnmower cutting the wire. The cut from a spade or work with a scarifier can also damage the cable or cut it completely. Occasionally, it is enough to get your foot caught on the cable.

But wind and weather also take their toll on the cable. Over time, the plastic sheathing becomes porous, moisture penetrates, and the wire can corrode or oxidize.

Finally, voles also like to nibble on the perimeter wire. They often don't bite through it completely, so the damage can go undetected for a while. In some cases, the purchase of a special wire that is resistant to biting can help.

Exclude sources of error

Often the cable is not cut at all but simply a connection is loose. Therefore, first check whether all connections are secure. In addition, dirty contacts can also lead to an interruption in the power supply. Clean the contacts on the charging station and spray them with contact spray. It is also possible that the charging station has become damaged. To determine this, you can build a test loop with a short piece of cable and thus test through the loops on the charging station.

It is also possible that the cable is not completely cut. In this case, depending on the weather, the robotic lawnmower may sometimes drive and then simply stop for no apparent reason. Since current still flows through such a cable, finding the fault can be is much more difficult.

Locating the broken cable

If the cable has been cut, generally an LED will flash on the charging station (fast red on Robomow if the connection is broken, slow red if the connection is weak). Many robotic lawnmowers will immediately stop operating. If such an error message is present, the next step is to locate the broken cable. Luckily, there are professional devices for this. Also possible is a medium-wave (AM) radio. Switch on a frequency (without a transmitter) and move the radio with the ferrite antenna parallel and close to the ground along the boundary cable. A hiss will be heard where the wire is intact. The hissing will stop and there will be silence or the noise may become quitter at or beyond the break point in the wire.

An alternative is to use a pasture fence device or, in severe cases, a DVM multimeter. When using a pasture fence device, it is important to disconnect the cable from the charging station beforehand. Otherwise, the voltage can damage  the charging station. After the device is grounded with the associated cable, connect the cable ends and turn on the device. A hissing sound can now be heard at the location of the cable break. Disconnect the unit from the cable again before repairing.

Disconnecting the power supply

Before working on the boundary wire, it is advisable to disconnect the charging station from the power supply.

Connecting a defective boundary wire

Signal interference occurs when the cable is cut. Simple solutions to reconnect the two ends are luster terminals or electrical tape. This may work for a short period of time, but keep in mind that when subjected to moisture, the wire may corrode and the connection will become weak.

Better suited are special connectors with gel filling which help keep moisture out , even underground. The two ends are simply inserted into the holes provided without insulating the cable beforehand and the connector is then pressed firmly together with a pipe wrench.

However, it often proves problematic if the wire has been laid tightly and is therefore too short to be plugged together again with a connector. One possibility here is to insert another piece of cable between the cable ends using two connectors.

Problem solved!

After repairing the boundary wire, the error message should disappear. If that is not the case and the LED on the charging station is still lit, it may help to press the connector together again with the pliers. There could also be multiple cable breaks.

Avoid cable breaks

You are never completely safe from a cable break, but the risk can be minimized. A sketch that accurately traces the course of the perimeter cable can serve as a reminder even years after installation.

When laying above ground, the cable must not be too taut. Otherwise, there is a risk of damage to the robotic lawnmower .

If there are voles in the garden, usually recognizable by bite marks on plant roots, it may be advisable to purchase a boundary wire with special sheathing.

Perimeter wire repair kits

Repairing the boundary wire is particularly simple and quick with a repair kit. These contain