Quick answer: Cat 6 direct burial cable uses a gel-filled core, a UV-resistant polyethylene jacket and often an armour layer. Indoor PVC cable absorbs water, cracks in sunlight and lets moisture migrate along the bundle. Bury at least 450 mm deep, keep 300 mm from power cable where possible, and test the run after backfilling.
Indoor cable buried in a garden works for a season and then fails in a way that is expensive to diagnose. The water does not enter at one point; it travels along the bundle and corrodes every conductor it reaches.
Why indoor cable fails outside
Water migration
A nick in the jacket lets water in, and capillary action carries it along the spaces between conductors. Copper oxidises, resistance rises and the link degrades long before it stops working. Gel-filled cable blocks that path, which is why the filling is the defining feature rather than the jacket colour.
Ultraviolet and temperature
PVC jacket material becomes brittle under sunlight and cracks at the bend points. Polyethylene resists UV, and burial grade cable uses it. Temperature swings also move the cable slightly, so the trench should be free of sharp stones and the cable should be laid with slack rather than pulled tight.
Construction and specification
| Feature | Burial grade | Indoor grade | Result |
|---|
| Core filling | Gel filled | None | Blocks water |
| Jacket | PE, UV stable | PVC | Survives sunlight |
| Armour | Optional | None | Rodent resistance |
| Temperature | Wider range | Narrow | Seasonal stability |
Installing the run
Depth and separation
Bury at least 450 mm deep, deeper under a driveway, and keep 300 mm from mains cable where the routes run parallel. Cross power cables at right angles. Add a draw cord in the same trench so a future cable can be pulled without digging, and photograph the route before backfilling.
Termination and testing
Terminate indoors where the cable emerges, with a service loop and a drip loop so water runs off rather than into the building. Test the link after backfilling rather than before, because settlement and stone damage show up afterwards. A certification test records the margin and tells you whether the run will hold 10G.
Protection and testing
Surge protection for outdoor copper
Any copper cable that leaves a building can carry a surge from a nearby strike or from an earth potential difference between two structures. Fit protectors at both ends and bond them to the building earth. A protector at one end only leaves the far equipment exposed, which is the more expensive of the two to replace.
Certifying the run
Test after backfilling and record the results. A burial run that passes on the reel can fail once stones press against the jacket, and the fault appears as intermittent errors months later. A certification report with margin figures tells you whether the link will hold 10G or only gigabit, and it is the document that supports a warranty claim.
Photograph the trench with a tape measure in frame before backfilling. That image is the only record of depth and separation, and it protects both the installer and the client if a later dig damages the cable. Add the cable route to the site plan, and keep the certification results with it.
If the route passes under a lawn that will be dug again, lay a second duct with a draw cord so the next cable does not require a new trench through established grass.
If the ground is heavy clay, add a layer of sand around the cable, because clay holds water against the jacket and moves as it swells, which is what eventually cracks an otherwise suitable burial cable.
If the property floods, mount the termination above the expected water line, since a burial cable that stays intact can still be destroyed by water entering the building through the same hole.
Practical scenarios
- Garden office: gel-filled Cat 6 in conduit under the lawn, terminated at both ends indoors.
- CCTV camera post: armoured burial cable where rodents are active.
- Gate intercom: direct burial run with a draw cord for a second cable later.
- Between buildings: fibre rather than copper where the distance or earth potential demands it.
FAQ
Can I bury ordinary Cat 6 in conduit?
It works if the conduit stays dry, which it rarely does. Gel-filled burial cable inside the conduit is the reliable combination.
Does direct burial cable need surge protection?
Yes for any copper run that leaves a building. A surge protector at each end protects the equipment from earth potential differences.
How deep should the trench be?
At least 450 mm, deeper under vehicles, with a warning tape above the cable.
Next step
Jacket and core options are detailed in Cat6 direct burial cable, general construction in Cat6 cable, and the audio equivalent in direct burial speaker wire.
See the matching cables and adapters
