A couple of weeks ago we were awoken by our house internal security alarm siren (it wasn't set) going off early one morning. This happens when the mains power is cut and the backup rechargeable battery discharges. On investigation I found that one of the earth leakage circuit breakers on the house consumer unit in the garage had tripped. Unfortunately, the house wiring is such that a variety of appliances were protected by the same trip switch so tracing the cause was a bit of a problem. My initial hunch was that due to the random nature of the fault it was being caused by something like a fridge thermostat operating.

After switching all appliances off and trying without success to reset the mains power I was on the point of acknowledging defeat and calling in a professional electrician. It was then that I remembered that the Triton was connected to the house mains via its ehu cable and an external blue wall socket that I installed some years ago. I generally leave the van connected on a plug-and-forget basis so that its three-stage Amperor charger can maintain the battery in good condition throughout the winter.

Once the van was disconnected I was able to reset the mains, get the freezers working again and deactivate the siren. But what was the problem with the caravan electrics? The only thing operating was the battery charger so that must be faulty, right?

When I originally had the van electrics modified to accept a more modern charger, I fitted a wall-mounted panel voltmeter so as to be able to keep an eye on the charging voltage and battery condition. A failure while touring on the continent had made me very aware of the need to monitor battery health particularly as I'm useless at reversing onto pitches and generally have to rely on the motor mover.

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When checking the battery to see if the charger was still doing its job, I found that the Lascar Electronics LCD voltmeter was missing its decimal point and a couple of bars from the display immediately after it.

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Could this be the problem? A mate who runs an electronics business soon ruled this out as a possible cause. His suggestion was to disconnect the battery charger from the mains inside the van, reconnect the cable and see what happened. He suspected a cable fault.

After a day connected, the house electrics tripped again and would not reset until the ehu was disconnected. It looked as though the battery charger wasn't the culprit after all. Phew, they now cost more than £100 to replace.

When I contacted Lascar Electronics for an identical replacement voltmeter I was quoted a total of £42 which I though a bit excessive as P&P was more than £8 for such a tiny component that weighs practically nothing. Instead I bought a 'Thlevel' voltmeter from Amazon (delivered for £10) that attaches to the wardrobe wall with a sticky pad and didn't require any further wood butchering on my part to connect.

I now suspected a fault in the wall socket itself so I hooked up the caravan to an internal socket in the house using an adapter extension and reconnected the battery charger inside the van. After a few hours the circuit tripped again. Bugger!

By this time I was practically tearing my hair out when the fair Mrs Calder casually remarked, 'Isn't there another orange cable in the loft that we used to use when we had the tent? Why don't you try that?'

As you know, the world hates a smartarse but on this occasion she solved the mystery. With the van connected to an indoor socket using this cable (it isn't long enough to reach the outdoor socket) the system works perfectly and cannot be made to trip the mains.

The conclusion has to be that my old 25m cable is somehow faulty and is probably leaking a few milliamps to earth due to corrosion or moisture and that that is sufficient to trip the mains. I've had the cable since I bought the van in 2011 and it has been out in all weathers since and is very faded. A new 25m 16A Semloh brand cable was £28 from Amazon.

One thing I have learned from this is that when it comes to electronic equipment, you get what you pay for. The Lascar voltmeter may be expensive but it is absolutely accurate whereas the Thleval brand meter at a quarter of the cost reads 0.23V high. So long as I remember to take that into consideration, I should be able to live with it.

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I'm pretty sure there must have been some very slight moisture in the plug(s), Steve, so that was probably the cause of my problem.

Everything seems to be fine since I fitted the new uprated cable. (Fingers crossed. )