Your home is on underground supply, and you're getting flickering lights, half the house going dead or the main switch tripping. Could it be the underground mains? It could. Underground consumer mains, the cable from the pit or pillar to your meter, are out of sight, but they're not maintenance-free. Water getting into conduit, damage from digging, root intrusion, ageing joints and cables pushed past their rated load can all cause faults. The good news is that modern fault-finding can usually locate the problem without trenching your whole property.

Signs your underground mains may be failing

Partial power loss. Some circuits dead while others work. On three-phase homes this often means one phase has failed.
Flickering or dimming lights, especially when big appliances start
Main switch or RCD tripping with no obvious cause in the house
Low or unstable voltage reported by solar inverters, EV chargers or smart meters
Heat, discolouration or a burning smell at the meter box or pit
A recent dig on the property, such as landscaping, fencing, a pool or plumbing work, followed by electrical issues

If you see sparking, smell burning or notice heat at the meter box, treat it as an emergency. Call us on 0402 559 777 or see our 24/7 emergency service.

Common causes of underground faults

Mechanical damage. Shovels, post-hole diggers, excavators and fence posts are the leading cause. Cables laid too shallow or without marker tape are most at risk.
Water ingress. Cracked conduit, failed pit seals and poor joints let water reach the cable, degrading insulation over time.
Tree roots. Roots can crush or crack conduit, especially near older trees.
Ageing joints and terminations. Joints in pits and at the meter are common weak points.
Overload. Adding EV chargers, batteries and ducted air-con to a cable sized decades ago causes overheating.
Ground movement. Clay soils that shrink and swell can stress cables and conduit.

How fault finding works

Safe isolation. We isolate the supply at the network connection point, which is Level 2 work.
Insulation resistance and continuity testing to confirm the cable is faulty and identify which conductor is affected.
Cable route tracing to map where the cable actually runs, which often differs from what old plans show.
Fault location. Specialist equipment narrows the fault to a short section so excavation is targeted.
Targeted excavation to expose and confirm the fault.

Repair or replace?

Repair (jointing) makes sense when

The fault is a single point of mechanical damage
The rest of the cable tests healthy
The cable is correctly sized for current and planned load

Replacement makes sense when

The cable is old, with multiple faults or widespread insulation breakdown
Water has tracked along the conduit
The cable is undersized for new loads like EV chargers or three-phase
The conduit is crushed or root-damaged along its length

Replacement often pairs well with a supply upgrade. If you're replacing the cable anyway, sizing it for three-phase or a higher capacity costs relatively little extra. See our three-phase guide.

What drives the cost

Costs depend on how quickly the fault can be located, excavation depth and surface type (lawn versus concrete, pavers or driveway), whether jointing or full replacement is needed, cable size and length, and any pit, pillar or meter box work. Emergency after-hours callouts cost more than planned work.

Preventing future faults

Call Before You Dig and locate private cables before any excavation
Keep a record of your cable route after any underground work
Avoid planting large trees over the cable route
Have the cable load-assessed before adding major new appliances
Include underground mains in a periodic condition inspection

Get your underground supply tested

Call 0402 559 777 or book a fault-finding visit. We'll locate the fault, tell you whether repair or replacement makes more sense, and get your supply back safely.

Underground Mains Faults in Sydney: Warning Signs, Fault Finding and Repair vs Replacement