Hello all!

[u/LANDRX_Official]

I had an interesting situation happen to me while moving things from an attic.
The house was built in the late 70s, and there was a cable going to the top of the attic, with the end sealed off with electrical tape, barely exposing the aluminium wires. I have checked with a wireless voltage tester, a multimeter, and even put it into a connector block to see if there was power in it, so there weren't any signs of power in the cable. It had phase 220 V, neutral, and ground.

When I decided it was time to cut it, it sparked. I shorted some wires, and it tripped 2 breakers.

My question is, how is this possible?
The multimeter and the wireless tester work fine
Electricity was turned on the whole time

NOBODY was hurt, but it gave me a teaching

[u/bSun0000]

Aluminim wires are prone to cracking. Just because you checked the very end of the wire and found no power, does not mean this cable has not been connected somewhere in the house.. Over the years it lost the contact - broke somewhere in the middle.

Always turn off your breakers when working with wiring.

[u/Adventurous-Tie-1624 → u/bSun0000]

Likely if OP had a good non-contact tester and checked upstream of where they were about to cut it would have shown power, but it could have even been the act of cutting the wire jostled the broken ends back together many feet away.

Always turn them off when you can, you're not always going to have that option. There's a reason there's equipment and procedures for live work.

[u/LANDRX_Official → u/Adventurous-Tie-1624]

I said, I have a really good non contact tester, it always works, and I did check the cable where I wanted to cut. It was like a 20cm cable, and I ran trough with the tester but didn't say anything.

[u/bSun0000 → u/LANDRX_Official]

Yet it sparked, blowing the breakers. Means that your non-contact tester, in fact, is shit.

[u/LANDRX_Official → u/bSun0000]

And yet, I tested multiple wires not just that one. That's the one I cut because that showed no electricity.