Finding a Short in a Buried Undergate Cable With a Fault Finder: Readings on Both Sides of the Gate, the Far Fence Switched Off, and Cable Re-Laid 12 Inches Down in Pipe

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When an electric fence reads strong up to a gate and weak beyond it, the buried cable under the gateway is a prime suspect. A fault finder that reads both voltage and current can tell you whether power is leaking into the soil under the gate before you dig anything up.

How do you tell if an undergate cable is shorting out?

Take voltage and current readings on both sides of the gate, close to each cable end. Then switch off the far fence so the cable is the only load. A big drop in voltage with a jump in current at the near end, while the far side stays weak, points to damaged insulation underground.

Virginia Cooperative Extension's Troubleshooting Electric Fences (SPES-692) says to test on both sides of critical points such as gates and lane crossings. It notes that fault finders only read about 100 feet in either direction, and that a major voltage drop with a significant rise in amperage usually means current is flowing out somewhere.

The same bulletin warns that friction with rocks can wear through the insulation on buried wire over time. Its fix is to always sleeve insulated wire in conduit when crossing under gates or other high-traffic areas.

Reading the Gate Crossing

Near side of gate	Far side of gate	Likely meaning
Strong voltage, normal current	Strong voltage	Cable is fine, look elsewhere
Low voltage, high current	Low voltage	Leak at or past the gate
High current, far fence switched off	Little or no reading	Cable is leaking to ground
Normal current, far fence switched off	Low voltage	Cable broken or a bad joint

The rows are a reading guide rather than fixed numbers. Every fence has its own baseline, so take a set of readings while it works well and keep them with the energizer.

Why the Cable Fails

The Gallagher Power Fence Systems manual says to carry power across gateways underground using double insulated cable. It calls for burying it at least 12 inches deep in soil free of stones, with plastic pipe for extra protection and the pipe ends bent down to keep out water.

The manual also says the cable under gateways must stay flexible to allow for strainer post movement and should avoid sharp objects. A cable pulled tight around a post corner or buried bare in gravel is the usual weak point.

Materials and Tools

• Electric fence fault finder that reads voltage and current with a direction arrow
• A cut-out switch at the gateway, if the fence doesn't already have one
• Replacement double insulated undergate cable rated for buried use
• Plastic pipe long enough to span the gateway with both ends bent down
• Joint clamps for the cable ends, a spade, and insulated gloves

Testing Steps

1. Record a baseline. Read voltage at the energizer terminals and on the fence near the house so you know what a healthy reading looks like.
2. Read the near side. Clip on within a few feet of where the cable leaves the fence on the energizer side, and note voltage, current, and arrow direction.
3. Read the far side. Repeat within a few feet of where the cable comes up on the other side of the gate.
4. Switch off the far fence. Open the cut-out switch so the cable is energized but the fence past it is not.
5. Read the cable alone. Check current again at the near end; with nothing past it, a sound cable should draw very little.
6. Turn the energizer off. Unplug or switch off the energizer before touching the cable ends or digging.
7. Call before you dig. Have buried utilities marked, since gateways often sit near water lines and wiring.

Re-Laying the Cable

• Dig a trench at least 12 inches deep across the gateway and clear out stones
• Thread new double insulated cable through plastic pipe, with both pipe ends bent down
• Leave slack at each post so the cable can move with the post
• Backfill with stone-free soil, then reconnect with joint clamps or through the cut-out switch
• Retest both sides of the gate and compare against your baseline

Gallagher also warns against relying on electric gates to carry power across a gateway, because power to the fence is lost when the gate is open. Keep the gate itself as a separate, switched piece.

Ground problems can look like a weak fence too, so rule them out with testing ground rods on a garden electric fence. For a multi-wire run, see testing a 5-wire polywire deer fence.

Where small animals tunnel under the gate, a strip of mesh pinned across the gap helps keep them off the trench line. The hardware cloth mesh size and gauge guide covers which opening to pick.

FAQ

Can I use regular insulated wire under the gate?

The Gallagher manual specifies double insulated cable for gateway crossings. Virginia Extension adds that buried insulated wire should be sleeved in conduit, because rocks can wear through the insulation.

Why take readings so close to the cable ends?

Virginia Extension notes that fault finders read only about 100 feet either way. Readings taken far from the gate can blend the cable with the fence on either side.

How low is too low on the far side?

Gallagher gives 3,000 volts as the recommended minimum fence voltage. If the far side sits below that and the near side doesn't, the gate crossing is where to start.