Flicker on lighting circuit

[umborne]

When I turn on a filament light on one of my lighting circuits, it comes on OK, but after one or two seconds brightens a little. Flourescent lights flicker a little and after two or three seconds begin to glow steadily and gradually assume full brightness as normal. This behaviour only affects this circuit; the other lighting circuits behave normally. What could be the problem? This only started a few days ago immendiately after I had cleaned some mains-powered smoke alarms which are also on the circuit. This involved turning off the power to the circuit via the MCB, vacuuming the alarms for dust and then turning the MCB on again. Could this be related to the problem or is it just coincidence?

 

[RF Lighting]

It could be related, but it's hard to know.

It certainly sounds to me like a loose connection somewhere in the circuit.

 

[umborne]

I thought "loose connection" as well, but the behaviour is shown by every light, and, as it is a radial circuit, won't this imply that the loose connection will be at or between the consumer unit and the first light on the circuit? I've checked these and they seem to be OK.

 

[RF Lighting]

Possibly, but it could be as the load of the failed lights is removed from the circuit, the volts drop is reduced (ohms law), so the remaining lights get brighter. This will also appear as flickering.

 

[umborne]

I can see that I'll just have to resign myself to methodically checking all the connections, but I think I'll start with those smoke alarms as they were the only things I'd touched when the problem first arose. Thanks for the advice

 

[Taylortwocities]

I would start at the MCB that you turned off.

Turn the power off at the main switch
Check the cable that goes in the top, make sure the screw is tight

Look underneath the MCB where the copper busbar goes across. Make sure that the busbar is connected inside the screw clamp (sometimes they get stuck behind the screw. If its OK, make sure the screw is tight.

Turn the MCB on and off a couple of times to 'clean' its internal contacts.

Check to see if things have been fixed. Then go check the smoke alarm connections. Remember to turn off the power if you are removing covers, etc!

 

[Space cat]

I agree with Taylortwocities; the MCB you touched is the prime suspect.

If you have a second lighting circuit on an identical MCB, you could try swapping the circuits over. If the fault now moves to the other lights, you have the culprit.

 

[umborne]

For those watching this thread, I worked methodically along the circuit and isolated the fault to - apparently - one of two junction boxes. I say "apparently" because the connections appeared sound, but when remade the fault disappeared. One of the boxes was quite dusty inside (it was in the loft) so I assume that must have had something to do with it. I dismissed the MCB quite quickly by disconnecting the circuit after about the first two lights. The fault disappeared suggesting the MCB was OK and that the fault lay beyond those first two lights. Thanks to all for your help.

 

[Taylortwocities]

Good job!