Why am I only getting 50V?

[parthianshot]

Hi everyone, I'm newly qualified (after a lifetime doing office work) and starting out on my own, so far so good.
I was called to a house yesterday to see why a loo light wasn't working and found the reading showing just 50v available. That was at both end, sw and rose.

The house was re-wired a few years ago and everything looks sound.
The only anomolay is there is a 3 core poking into the rose but not connected, it doesn't go to the sw though? Could that be related?
The homeowner says the light was working fine until recently and there wasn't any incident that might be related.

 

[SMB]

did you test between L/N, L/E and N/E?

I doubt the unconnected 3core has anything to do with your problem.

Im no expert but what you need to be doing is tracing the cable which is feeding the loo light because that is where your problem lies.





a lost neutral ?



if all the other lights in the house are working correctly then your problem is with the feed to this light. Its probably just a loose connection.

sorry I cant help more but im not there.

 

[Deleted member 9648]

Presumably the light is not wired 3 plate?....in which case it must be a poor connection in a JB or something.

 

[BlueToBits]

Check the voltage L-N L-E and N-E with and without a standard lamp (not low energy) with the switch in both the on and off positions. This will give a better idea of the cause of the problem, but it is probably irrelevent as it sounds like you will still need to get above the ceiling or below the floor above, if everything checks out in the accessories.

 

[geoffa]

do you mean you only have 50v at both ends of the switched live conductor?

Have you checked between L and N, and L and CPC?

Have you checked all terminals have good connections on conductors ie not tightened onto insulation or loose

what voltage do you have at the loop connector in the ceiling rose and the live on the common terminal on the switch?

it may be that you have a faulty switch or an induced voltage that shows you have 50v on the switched live conductor.

Test between the 2 live conductors at the ceiling rose that go to the switch with a continuity test to make sure you have a circuit with the switch in the on position.
If no continuity or high resistance then measure continuity across the switch terminals to eliminate cable.
If switch is ok then connect a long test lead between the live conductor out from the ceiling rose and the opposite end where it terminates on the switch.
If ok do the same between both ends of the switched live conductor.
If you don't have a long test lead you could try using the CPC instead.
If using a long test lead remember to zero your tester

 

[SMB]

geoffa......sounds like someone is studying their 2391?

 

[geoffa]

was an industrial maintenance electrician, passed the 2391 few years ago

 

[parthianshot]

Good advice thanks. I tested the whole light circuit and found everything seemed to be in order.
There's a ceiling rose in place and I'm assuming it loops in from another light. Oddly this circuit feeds just the sitting room which is across the house from the loo. So following adviCe here do I need to find where the last connection was before the toilet and check that for tightness etc?

 

[i=p/u]

id say yes find where that feed comes from

 

[BOROROBBO]

"the light was working fine until recently". im sure we have all heard that one before but upon closer inspection they have bodged some DIY electrics and dont know how to put it back to how it was.

have a GOOD look round for any work that looks recent. i.e. any floorboards that look like they have been lifted, any filler/plaster on the walls that looks fresh etc etc

get a photo of the light fitting up or some kind of drawing. how many cables into the light fitting? is your 50v between switch live and neutral or between live and neutral?

 

[SMB]

any new shelves or pictures on the wall?

 

[needasparks]

any new shelves or pictures on the wall?

My wife askes me that every week, before getting the hump. lol

some good detective work before getting the tool box out will save alot of time as everyone has given you the usual things to look for.
When i started i used to dive in head first and not see the most obvious things, take a step back and think about it first.

Don't always work but as a rule of thumb if it less than 30v to earth its a lost live, less than 110v its a lost neutral, should be basic check to earth/neutral to find the fault then you have a better idea what to start looking for.

 

[telectrix]

quite often you may find a broken cable on the termination at the fitting preceding the one that's not working. either that or a poor connection.

 

[nikmet]

always give the cables a little 'tug', as the screws can be tight, all looks good, but the conductor on close inspection has snapped, especially 1mm