A clamp meter around a live cable tells you what is flowing through it, and a cable that feeds nothing carries nothing. This one carries nine milliamps, and the other end of it is under a netball court.
I am an electrical contractor and I do the fixed wire testing on about thirty schools.
What the test is, briefly, because the numbers are the story.
Every five years a building's wiring gets inspected and tested and a report is issued. You dead test: continuity, insulation resistance between conductors and to earth, polarity. You live test: earth fault loop impedance, and the trip times on the residual current devices.
Insulation resistance is the one people know. You put five hundred volts across a circuit with the load off and measure how much gets through, and you want hundreds of megohms, and anything under a megohm is a problem.
And you carry a clamp meter, which measures current without breaking into anything, by reading the magnetic field round a cable. Clamp the live and neutral of a circuit together and you read the difference between what goes out and what comes back, which is the leakage, and on a healthy circuit it is a fraction of a milliamp.
Way 14 in the distribution board in the plant room of this school is labelled ANNEXE.
There is no annexe. The annexe came down in 1998 and the netball courts are on top of it.
The cable is still in the board, on a thirty two amp breaker, and it leaves the building through a duct in the floor.
It carries nine milliamps.
Nine milliamps with nothing on the end of it.
A cable feeding nothing reads zero. Not nearly zero. Zero, because current needs a circuit.
What I did about it on the day, which was 2019, and in order.
I checked the clamp. Zeroed it, clamped it round a cable I knew was dead, read nothing, clamped it back, read nine.
I switched the breaker off. The reading went to zero, which is correct and which tells you the nine milliamps is coming out of that breaker and not induced from something lying next to it.
I did the insulation resistance test on it, which is the real test for a damaged cable in the ground. A cable crushed in a duct, or with water in it, leaks to earth, and that is exactly what nine milliamps looks like.
Two hundred and ninety megohms line to earth. That is a healthy cable. A cable leaking nine milliamps at two hundred and thirty volts has an insulation resistance of about twenty five thousand ohms, which is nought point nought two five megohms.
Those two measurements cannot both be true.
I did them four times, and on the fourth I had the site manager hold the leads.
What has happened since.
I wrote it up as an observation on the report, coded as requiring further investigation, with the figures.
The local authority's property team asked for a quote to disconnect and remove the circuit, which is what any sensible person does with a cable to a demolished building, and I gave them one, and it was approved, and in 2020 I went back to do it.
You cannot safely pull a cable out of a duct you cannot trace, so the job was to disconnect at the board, cap the tails, and label it.
I disconnected it. Capped both ends with proper boots, isolated the way, labelled it SPARE, DISCONNECTED, and wrote the date on the label.
It is a dead length of cable with nothing connected to either end.
I have been back three times since, because I hold the contract.
In 2021 I clamped it because I was curious and because it took four seconds.
Nine milliamps.
Not the board's cable, which is capped. The cable. Clamped about a metre before the cap, where it comes out of the floor.
2023 the same. This spring the same, and this spring I borrowed a better meter off a colleague, a true RMS one that reads down to a tenth, and it says nine point one.
What I have done with that.
Nothing, and I will tell you exactly why, because it is not bravery and it is not dismissal.
There is no electrical danger. A capped cable with nine milliamps in it cannot shock anybody, because there is nothing to touch and nothing it can flow into. The court above it has a sixteen year old surface and a perimeter fence and forty children on it at break.
And there is no report I can write. The form has boxes for a circuit and a reading and a recommendation, and the recommendation for a cable like this is to remove it, and I have already done the part of that which is possible without digging up a netball court.
So it is on my own list, in a notebook, as way 14, and I clamp it when I am in that plant room because I have stopped pretending I am going to walk past it.
The figure was nine point one in March. In 2019 it was nine point zero on a meter that only read to the whole number, and I have no way of knowing whether that is a change or a better instrument, and the next test is in 2029 and I have already decided that I am doing it myself rather than sending one of the lads.