I wonder how many of you have seen the interesting problem of LED lamps and loose connections?
A friend of my Partner recently moved into a new flat. She replaced all the lamps with LED options and a new and before invisible problem showed up, two of the new LEDs flashed on and off at perhaps 0.5 Hz, sometimes, but noticeably when the CFL outside light was switched on and they were already on.
Changing the LED lamps made no noticeable difference so B&Q got away with that! Fitting filament lamps made the problem go away. I wonder what was happening?
Carefully trying to measure the supply voltage at the ceiling rose gave a clue, when catching the lamps flashing (only sometimes, the rest of the time normal light) indicated about 40-50 volts, and 240 ish when they worked normally. Cable continuity measured OK, there was a fairly complex set of 2 way switches and looping in to disentangle, but removing the switches indicated a number of loose screws, and one connection where two live loop wires entered but only one was caught by the screw. The start current of the CFL was sufficient to make a good contact of this loose wire, and sometimes it connected, but at other times it was several thousand Ohms! With the higher current of normal filament lamps the connection made good contact, with about 50mA of LED it was not reliable.
With about 50V the lamps would start, but then as the smoothing capacitor discharged they had insufficient voltage and went out, the time constant being about 2 seconds. I have now seen this twice, and it is at first look very odd indeed. There are many installations out there with loose connections which work fine with larger loads, but as the LED currents are small the contacts no longer spark slightly and self-clean. AFDDs would be useless, and the situation is not dangerous because of the low current.
