Why This Matters to You
An underground fault is the most frustrating kind, because there's nothing to look at. The cable is a metre under the ground, the fault could be anywhere along its length, and the only thing you can see is a safety switch that won't stay on. The usual response is to reset it, get a few days out of it, and reset it again.
This one was at a soccer club in Golden Grove. Their lighting kept tripping, there had been construction work nearby, and the tripping was getting more frequent. Here's how the fault was found and what was actually wrong.
Finding a Fault You can't See
The temptation with a buried cable is to start digging where it seems most likely. That's an expensive guess, particularly across a sports ground where the surface has to go back the way it was found.
The work happens before the shovel comes out. The circuit gets isolated and tested to confirm the leakage is real and to establish which conductor is involved, because a fault between an active and earth behaves differently to a fault between active and neutral, and that tells you something about what you're looking for. From there the fault is narrowed down to a position along the run rather than a general area, so that when the ground is opened it's opened once, in the right spot.
That approach is the difference between a morning and a week, and on a site with a playing surface it's also the difference between one small excavation and a trench across the ground.
What Was Actually Wrong
Two things had happened. Construction work nearby had disturbed the ground and damaged the cable. But the point that actually failed was a join in the cable that a previous electrician had made and buried.
A join that's going to live underground has to be sealed against water for the whole of its life, because the ground it sits in will be wet for part of every year. This one wasn't, and moisture had been getting into it. The conductors had corroded to the point you can see in the photo below, and corroded copper in wet ground leaks current to earth. That leakage was what the safety switch had been detecting.
None of this was visible from the surface, and it would have been invisible on a visual inspection of the switchboard as well. The only symptom available was the tripping.
Repairing It Properly
The damaged section was cut out and remade as a resin-filled joint. The joint goes into a shell, resin is poured in, and it cures into a solid block around the conductors with no path for water to reach the copper. That's what a buried joint is supposed to be, and it's the reason the repair will outlast the original.
The conduit was repaired at the same time. Leaving a damaged conduit and relying on the cable alone means the next person to dig has nothing to warn them, and the cable has lost the mechanical protection it was supposed to have.
The Safety Switch wasn't the Problem
This is worth saying plainly, because it comes up constantly. A safety switch that keeps tripping is almost never a faulty safety switch. It's a device doing exactly what it was installed to do, telling you that current is going somewhere it shouldn't.
Repeatedly resetting it isn't a fix, and replacing it because it seems oversensitive removes the only protection standing between a fault and a person. If you have a circuit that trips after rain, or trips more in winter than summer, moisture getting into something is the first thing to suspect. Our page on safety switches and RCD testing covers how they're properly tested.
If Your Circuit Keeps Tripping
Note the pattern before you call. Does it trip at a particular time of day, after rain, when a specific light or appliance comes on, or at random? That pattern is genuinely useful diagnostic information and it can save an hour of testing.
For clubs, schools and businesses there's a second reason not to leave it: lighting that fails without warning is a safety and liability problem before it's an inconvenience. If it needs sorting the same day, that's what our emergency electrician service is for, and we cover Golden Grove and the surrounding suburbs from Wynn Vale. There's more on what we do locally on our Golden Grove electrician page.
