We've recently had an extension built at home, and during the process we've fitted 4 network cables into the new room as it's going to be used as an office.
I've connected all the sockets up and tested them with a network tester, however every single socket has issues. All of them have lights not lighting up when the tester checks each cable, and on some two lights appear at the same time.
On one occassion, disconnecting a cable from the socket suddenly forced others to work.
It looks like for 10 centimetre or so the cable pass right next to power cables, and I wondered if this is likely to cause all cables to fail?