Half the flat went dark - MCB did not trip

[solpap]

Hello everyone!

I have a problem with my lights. This is my story....
my girlfriend yesterday attempted to turn on the bathroom lights, and suddenly half the flat went dark.
The rooms affected were: bathroom (4 recessed spot lights and 1 small fan extractor), kitchen (5 recessed spot lights), and lounge (2 wall lights and 1 ceiling lamp). So, I went to the consumer unit (or fuse box) thinking that something triped. However, all fuses were "UP".

In my consumer unit I have WYLEX MCBs and also what appears to be 2 main switches. I think one switch controls the upper row of fuses and the the other the lower one. From the labels and from testing what is controlling what, I think the MCB controlling the circuit is the lower one (WYLEX B16), because whether it is on or off nothing seems to be affected. unfortunately all the other MCBs in the box are different amps so I cannot try to put another in (I mean to swap them).

The lights used to work fine, without any previous problems, so I dont think it was an overload. Also the fact that all fuses were on and none triped, means there is a short circuit somewhere???. I made a visual inspection of the bathroom spotlights but I did not see anything abnormal (mind you I am not sure whether I would recognize a blown spotlight - I ve never seen one!).

Any ideas?? If it is the MCB that I need to replace, I noticed that they sell them with the corresponding base (B16 is blue). Will I have to replace the base in the consumer unit or can I just use the existing one? Is there anything I should look for in order to diagnose the problem? (i.e. anything on the MCB that may indicate that it needs replacing).

Any help much appreciated! Thank you!
Solomon

 

[JohnD]

1) the lighting circuit should be on a B06 MCB (6Amp). there is often an upstairs lighting circuit and an independent downstairs circuit.

2) Lighting circuits are connected in a string like beads on a necklace (not joined in a ring). So if half your lights have gone off, on the same circuit, then there is likely a bad connection. It will be either at the first lamp in the string that is off, of the last one, before that, that is on.

You can turn off the power and have a look in the ceiling roses for burned or loose wires. Start in the bathroom as that is where there was an action that seemed to trigger the fault.

Look in the FAQ section or our Wiki for how lighting circuits are done. Do not disconnect any wires without drawing a diagram and marking each wire for how it is connected (there will be several of the same colour, and they are not the same). It will be easier for you to fault-find if you have a multimeter (£10 or less in the high street). Do not work on live circuits, and test that they are dead before touching anything.

Do not disconnect anything in more than one place at the same time. This is especially important with lighting circuits as people usually create extra faults by reconnecting roses and switches wrongly when they have taken them apart.

It is also possible that a cable has been damaged, e.g. by a nail through the floor.

It is very common for a spotlight to blow when it is switched on, and the surge to trip the MCB. You can check by switching off each MCB (one at a time) and seeing what appliances go off and on.

If you can put up a photo of the CU that may help us understand your installation.