Mystery lighting circuit problem..

Hi all, I'm posting on here out of desperation; I've spent the past two days trying to diagnose a problem with the downstairs lighting circuit.

Everything was fine until one evening earlier this week I turned on a light in the hallway downstairs and it didn't come on. I assumed the bulb (a standard incandescent one) was gone so went to the sitting room and the light there didn't turn on either, the bulbs (which are CFL) flickered every couple of seconds, but didn't kick in fully.

I've tested all of the switches work, and have confirmed that there is voltage at the ceiling rose terminals with a mains tester when there should be - i.e. voltage there when switches are on, not when switched off. The bulbs have all been tested and definitely work.

I've even taken a bayonet socket from an old lamp and used that to wire into the ceiling roses to check that there is current getting there - there is, but it just seems to be too low to illuminate the bulbs - even the incandescent bulbs wont glow so the current must be very low, but still there. The CFL bulbs are flickering presumably because the boost capacitors in there are charging up and eventually gaining enough charge to make the tube flicker, but not enough to illuminate properly.

I've switched the upstairs and downstairs breakers to rule out that issue too. The breaker didn't trip when the initial fault occurred, but still operates as when I introduce a fault to the upstairs light circuit after switching them. Upstairs light circuit works fine with the downstairs breaker installed.

Any idea? It seems like the downstairs lighting circuit has dropped current, but I can't fathom why, or how to put it right (short of calling in a sparky who will just rip everything out and put a new lot in...).

Advice greatly appreciated.

The amp part is not relevant really as load in amps is a product of voltage and power.

When you say you tested for voltage what did you get at the rose 230v?

MalcofArabia said:

The amp part is not relevant really as load in amps is a product of voltage and power.

Click to expand...

It most certainly is not. Suggest you check your electrical theory.

I haven't fully read your post yet, but as soon as you mentioned the flickering bit, I thought... missing neutral. Exactly what sort of 'mains tester' is it that you're using? A neon screwdriver by any chance? If so, chuck it away.

Could also be a high impedance connection on the line side somewhere, although again unless you're using a proper 2-pole voltage detector you're wasting your time trying to fault find this.

Yep, it's a neon screwdriver, is that an issue? Not got a mains-rated multimeter, just a pocket-sized one with permanently attached pointy probes, most of my electrical kit is for cars rather than houses. Is it worth getting one for this?

High impedance connection is intriguing - aside from bulbs, there is an extractor fan with a light over the hob (rarely used), and under-cupboard halogen spotlights. They're Ikea ones and powered by little DC transformers around the kitchen. They've always been a bit tempramental, bulbs tend to flicker quite often, assumed that it was down to the cheaponess of Ikea lighting... Will try removing those lights from the circuit this eve. Hoping that's it as I don't fancy digging into the extractor fan unless I have to!

Thanks for the feedback thus far.

you need to buy a proper multi meter and test for 230/240 volts at the rose.

how did you measure current with a neon screw driver?

sounds to me also like you have lost a neutral somewhere. You say you put a fault on the lighting circuit to get it to trip out - dont do this! there is no need and could be dangerous if your not sure what your doing.

you have a loose connection somewhere..
now be honest and own up, what fittings or switches have you messed with recently?
or what other DIY work have you done that involves the downstairs ceiling or upstairs floor? ( screw / nail through a wire possibly.. )

go round EVERY switch and ceiling rose and tighten every screw in there.. and look for broken wires while you are at it..

davelx said:

MalcofArabia said:

The amp part is not relevant really as load in amps is a product of voltage and power.

Click to expand...

It most certainly is not. Suggest you check your electrical theory.

Click to expand...

Do you ever actually read anything before you decide to impart your pearls of wisdom.

The OP in his question was referring quite a lot to current being low and not a lot of current there. Which I pointed out to him in this context current is not relevant as he would not be getting any if the light wasn't working would he!!! unless he was taking an amp reading at the CU where he would be getting a load off the circuit from lights that were working, but I've yet to find a piece of equipment not working that produces a current!!

i'm not going to explain ohms law as I'm sure you know it.

That is why I asked if he was getting 230V at the rose because I like others here thought the same he was using a neon screwdriver, and he answered yes and so immediately other members posted what it most likely is a neutral fault.

Do you ever read what you type before you post it:

"load in amps is a product of voltage and power"

So, A = V * W does it? This is not directly to do with Ohms law.

basic arithmetic: W = V * A - rearrange the equation gives A = W/V - that is NOT the PRODUCT. To get the PRODUCT you have to MULTIPLY the values. When you DIVIDE two values, the result is the QUOTIENT.

That is most impressive and we stand in awe of your knowledge of mathematical equations, As you quite rightly say product is a multiplication terms in the context of mathematics.

If though like me you were using it in a grammatical context, a product is something produced as a result of a process or system, so in that context I was using amperage as a product of watts and voltage irrelevant of division, addition, subtraction or multiplication, that is why I never gave the ohms law formula as I would then be referring to a mathematical product.

I'm sure the OP is mightily impressed in your grasp of electrical theory but it did not help him really did it. I was trying to make sure he was actually getting 230v at the point of testing as without that he was not able to get the light to work and therefore amperage was irrelevant as there would not be any

Dear, gopey - ignore all the interneceine warfare. Your problem is almost certainly a loose connection in one of the ceiling roses, possibly even a broken one. When the insulation is trimmed off a piece of wire the trimming action often cuts into the copper. Not much, but just enough to make a weaker point. Eventually this weak point may succumb under load, and break - just like a bit of fuse wire.

To find the problem go round each ceiling rose in turn, gently pull at each of the wires to see if any are loose or broken. Tighten all the terminals (some will be a bit loose anyway) and remake any connections you find that have broken.

Don't forget to isolate the circuit first ....

PJ

and dont use a neon screwdriver as a mains tester again!!

gopey said:

Yep, it's a neon screwdriver, is that an issue? Not got a mains-rated multimeter, just a pocket-sized one with permanently attached pointy probes, most of my electrical kit is for cars rather than houses. Is it worth getting one for this?

Click to expand...

You need a 2-pole voltage detector:



All a neon screwdriver can do is show you the potential between the tip of the screwdriver and a high impedance earth through your body, and they don't always do that reliably. You need to be able to measure between two points. When you do this, you will probably find that there is 230v between L-E, and next to nothing between L-N. That would suggest an open circuit neutral, which is still where I'm hedging by bets.