HELP! Can't Find Fault with Lighting Loop

RussellJColvin · 08-05-2008, 05:28 AM

Hi all,

Found this forum on ASK so hope you can help me. I am a DIY enthusiast and am fairly experienced in most fields, therefore, changing a ceiling light was a no brainer as I have replaced all of the others in my house at some point. This time though, my wife was nagging whilst I was changing it and the Black live returning from the switch got confused with the nuetrals (No Red Sleeves used in my house). So when I thought I had finished and turned the power back on and switched the light on, the fuse blew (Obviously!!).

So, I took the fitting apart, realising what I had done and not having a testing screwdriver or multimeter, I found the live switch return by touching earth to each of the black cables until the fuse popped again. This worked a treat! And I have now wired light correctly and fixed to ceiling, I reset the trip and tried light again, nothing!! No light? No Pop? weird!!

The thing is, the only light to work on the loop is the bathroom light, the landing, and all 3 bedrooms are dead?

I have checked the loop lives and they are all joined together, as are my nuetrals in the new light?

Has anyone got any ideas to help me out? any suggestions appreciated and will be checked.

Thanks!!!

Russ

Charles · 08-05-2008, 08:29 AM

I would suggest using a multimeter and narrowing down exactly where you are losing power at, which will help you to figure out the problem.

Electrical work can seem very overwhelming, but usually if you break it into sections it is not as bad.

When working on cars I start at the point farthest from the battery and work inward, taking it one leg at a time. This will help you narrow it down and since your bathroom light works, the problem is likely between the bathroom light and the next leg.

RussellJColvin · 08-05-2008, 08:37 AM

Thanks Charles, I'll work my way around the light fittings tonight and see where it loses power after the bathroom.

Hopefully it'll be fairly straight forward but I just can't imagine what would have broken the circuit? It would have to be a physical break wouldn't it?

Charles · 08-05-2008, 08:47 AM

Quote:

It would have to be a physical break wouldn't it?

That would stand to reason, but people do some crazy wiring...

theatretch85 · 08-05-2008, 08:51 AM

Um, the shorting the hot wire (or in your country the "Live") to ground probably wasn't the best idea. Its very possible there was a loose connection up the line somewhere and creating this short circuit to ground may have caused that loose connection to open up. Id check the box in the bathroom and make sure all the connections are secure in there first, probably a loose wire nut.

The best way to check for the hot or "live" would be with a multimeter or even a simple neon bulb (little tester with two leads coming out) simply tests and verifies that there is power there. Just don't short the wires to ground, that simply is not the best way to do it!

Also, please put your location in your profile, its obvious you are not located in the US. This site is mostly US based, and I would hope with your description of the problem people can figure out that you must be in the UK or overseas somewhere and not in the US. We use different colors of wires and terminology is different as well.

Ash · 08-05-2008, 05:40 PM

A neon bulb on its own is bad. As soon as it lights up its resistance disappears and you get shocked. It needs a resistor of at least few hundred ohms (1 Mohm is whats used in rester screwdrivers)

If you use a tester screwdriver it is ok - the resistor is allready inside

Stubbie · 08-05-2008, 06:47 PM

Quote:

This time though, my wife was nagging whilst I was changing it and the Black live returning from the switch got confused with the nuetrals (No Red Sleeves used in my house). So when I thought I had finished and turned the power back on and switched the light on, the fuse blew

Don't blame this on your wife......

that will get you whacked!!!

As you probably know the UK underwent a color code wiring change in 2004. The old colors for single phase

Black = neutral
Red = live
green/yellow = earth

new colors are

Blue = neutral
Brown = live
Green/yellow = earth

Below is a ceiling rose which is very similar to what you should be looking at. If you notice the old colours are in the existing wiring but the new fixture has brown and blue wires. Green/yellow earth has not changed. It is important that you get this straight when connecting your wiring at the rose.

In your case you have a red and black loop to the switch from the rose. black should be your switched live as you indicated (coming from the switch).

However it would not be your incoming power at the ceiling rose a red wire should be doing that job. Please refer to this diagram....

So my suggestions are to reset the breaker in the CU and look at the ceiling rose to see if the power to the other light circuits is correct on the connection bus and check voltage for 250 volts to earth at the live terminal where all power goes on to the other lights. It would appear that you have no voltage on the live terminal in the ceiling rose. Same connection check for the neutrals, which should be black in your case...except for the switch loop where black is being used for switched live. Should have no voltage on the neutrals to earth. As you say your switched black is not sleeved red so be cautious in your connections at the rose to be sure you don't miswire.
Everything being correct then you may have another blown fuse at a spur in the wiring downstream of your light. This would be in a plug box not a switch box.

Now on another note though creating a ground fault will definitely blow a fuse it also causes massive amperage to flow in the wiring till the breaker in the CU opens. There is quite a bit of released energy that can cause connections to fail. So I wouldn't take this short cut in the future.

In the USA we use wirenuts for joining wires in the splice boxes in your country you use terminals as shown in the diagram, check these for correctness and secure all the wires. No power on the loop of course.

Yoyizit · 08-05-2008, 09:34 PM

Use a 4w or 7-1/2w lamp as a tester to eliminate phantom voltages,
but using the bulbs will trip upstream GF devices.

Neons work on 1 mA and can still fire with phantom voltages, and DVMs pull even less current.

With a 1000 ohms/volt [that is, 1 mA through the meter movement gives a full scale reading] analog VOM, the reading you get on a phantom voltage will depend on the range you select.

RussellJColvin · 08-07-2008, 02:13 AM

Wow, thanks everyone for your help. I blamed the wife on here but never to her face. Coward or sensible? I'll let you decide!

I checked all the loops and found that there was power to all ceiling roses, then checked the Hallway light and faund that somehow a neutral cable had come loose. I re-connected and all is working fine now.

Strange how this coming loose coincided with me blowing the fuse, I hadn't touched the hallway light for months!!

Thanks again!

Russ

Ash · 08-07-2008, 05:46 AM

And it was not affected by the second time short circuit current either cause it is neutral

Maybe you pulled it from the other end a little when working on the other fixture

RussellJColvin · 08-07-2008, 05:48 AM

Yeah, hadn't thought of that!

Thanks!!

fw2007 · 08-07-2008, 02:59 PM

I would seriously consider buying a simple voltage tester (a neon lamp with leads, mounted in molded plastic) for a few bucks so that you don't have to short the hot (live) wire to the box to find out it is hot. Much better for you, and for the wiring!

FW

RussellJColvin · 08-07-2008, 03:10 PM

Thanks FW2007, I bought an electrical tester driver which has a little tester bulb in it for future problems!