I recently went to a job where the customer was complaining that their telephones were not working. They had several cordless telephones around the house and none of them had a dial tone. After a quick look, it was obvious to me that the master phone which is actually plugged into the land line socket was not getting power. I traced the power cable to a hidden socket behind a cupboard and when I tried to unplug it, I found it was completely stuck. This obviously caught my attention and after a closer look at the plug and socket I new I was close to finding the fault. After a couple of minutes of trying to get the plug out of the socket I realised that this was a lost cause.
so I removed the socket from the wall with the plug still attached. It was then very obvious we were dealing with a loose connection.
As you can see from the pictures the connection between the live wire and the socket terminal had become very hot, judging by the age and condition of the socket it was obviously old. I would imagine this was caused by the heating and cooling cycles produced when a load is turned on and off over years of use, after thousands of these cycles the wire either "settled" as the copper core softened slightly with the heat or the terminal screw loosened slightly.
With this type of fault as soon as the connection has started to loosen in any way it is only a matter of time before it completely fails as the looser it gets the more heat is created by the electricity effectively jumping the gap between the wire and the terminal, (the gap will be microscopic to start with).
It is worth noting that the only sign of the fault at this stage to the customer was a slightly fishy, burnt electrics smell around the socket and obviously eventually the socket stopped working. It did NOT trip any fuses or circuit breakers and would not of tripped an RCD if there had been one until it had become quite a bit worse. the solution was pretty simple, I cut the cable back to a point where it was no longer showing signs of heat damage, luckily there was enough spare in the socket box and I installed a new socket face plate. Unfortunately the customer had to buy a new power supply for there phone as the original was inseparable from the old socket.
So, could this have been avoided? Yes an electrical inspection should have picked this up as the socket was cracked as shown in the first picture and a test would have shown a high resistance reading at that socket outlet leading to the socket being opened up for further inspection. This obviously show how an EICR (Electrical Installation Condition Report) is something all electrical installations should have periodically.