Strange Lighting Circuit Problem....

[Sampletime]

The other night, my son turned on the upstairs lights and the landing light flashed and all the upstairs lights went out.

I was out but my wife sensibly checked the consumer unit and the MCB had tripped (good).

She reset it but none of the lights upstairs worked.

When I got home, I checked and removed the bulb which had shorted internally. The ceiling rose/fitting looks fine, the MCB is reset, but no power to upstairs lights.

I figured the MCB may have failed, so I swapped the downstairs and upstairs circuits between my two lighting mcb's. the downstairs lights worked fine off the upstairs MCB but the upstairs circuit did not work off the downstairs MCB. Conclusion, MCB is ok. 

Problem is I can't understand what the failure mode would be.... MCB is ok, fitting looks ok. Unless a wire had burnt out or a wire had come loose elsewhere in the circuit, then I can't think what might have happened.

Next step may be an electrician, but I'm quite capable of standard checks and so on, so is there anything I can check before I get somebody in?

Thanks in advance

Paul

 

[Steve3948]

Sounds like a loose connection at first light.

 

[batty]

What test equipment do you have? 

 

[SLIPSHOD & SLAPDASH]

Obviously a loose connection near the begini

Sounds like a loose connection at first light.

Agree, it could be on the line or neutral. The short circuit was enough to blow the loose connection apart

 

[Sampletime]

I have a digital voltmeter, so I suppose I can start testing voltages across the upstairs circuit, but it seems so strange that another light would coincidentally become loose at that point in time. 

Im not sure which is the first light to be honest....

 

[SLIPSHOD & SLAPDASH]

Or it could be the neutral at the board

 

[Sampletime]

Could a short literally force a connection apart mechanically? 

Obviously it's a radial circuit I guess, so I suppose one break would make the whole circuit open.

 

[steptoe]

first thing

turn the power OFF

you can then manually simply give each wire a gentle tug in turn, and it may be apparent

if you feel confident enough then the consumer unit would be the best place to start,

checking both the LINE [live] and neutral wires,

as said before, do all the dead checks before attempting any sort of live checks.

deffo sounds like the short has blown off a loose connection somewhere.

Could a short literally force a connection apart mechanically? 

Obviously it's a radial circuit I guess, so I suppose one break would make the whole circuit open.

if it was a loose connection to start with the arc could have melted the 'small' contact patch that existed,

yes, its a fairly common ocurrence in such scenarios.

 

[batty]

It does seem odd but you need to test start at board as slips says make sure neutral has good connection and copper is connected.

 

[betty swollocks]

You will probably have a loop in loop out set up so it would make sense that the incoming supply to the first light is the problem, either a broken live or broken neutral in the ceiling rose, as you said the landing light flashed and the lamp had failed that's where I would look first. Check with your meter that you have 230v between line and neutral, if you do that light should work. Be careful and make sure you disconnect the supply first before opening the ceiling rose because if there is a loose connection you won't want to touch it by mistake.

 

[kme]

Set your meter on "resistance", and turn the main switch "OFF" before you start - as said, a poor connection blown apart could leave a potentially live wire where you wouldn`t expect to find one.

As said, I`d also start at the fusebox - check all the neutral wires carefully - not just the terminations ( which could look okay, but have broken just inside the insulation) ; but also at any sharp bends in the cable - you can usually "feel" a broken wire within a cable.

If you do not feel confidant - don`t do it. It won`t take a competent sparky long to find it - ergo it isn`t an expensive job

Let us know how you get on, please?

Thanks

 

[Evans Electric]

Start with your landing light fitting , as Stepps says turn the circuit OFF and have a pull & a tug at the wires in the ceiling rose.

When lamp filaments  blow a high fault current flows for a split second , thats why the MCB trips .    Its much like a fault current really and a loose connection can fail under that condition .   Could be the live or the neutral  and is probably in the first fitting seeing as all the lights are off.  

Also as said , it could be in the consumer unit ..you've reconected the live but it could be the neutral .

I did a similar fault a few weeks ago , upstairs lights , sometimes they worked , sometimes they didn't .  I stuck my head up the loft hatch , touched a cable , theres a crackle from a joint box and all the lights came on ..........loose neutral connection crackling & arcing......... half a turn of the screwdriver and that'll be £40 thank you .

Edit :--    Yes as the guys have said above ....and  if the live and neutral are leaving the consumer unit, chances are they are in one of the fittings upstairs ..you're looking for the first fitting or a J/B  in the loft or  is the loft light the first one in line ...has an amateur replaced any fittings up there.? 

 

[Sampletime]

I'm really grateful for the quick and detailed responses...... I'll undertake the simple checks (safely) and let you know how I get on.

Will be on Saturday, so I can have a clear day with the power off if necessary.

Thanks again,

Paul

 

[Sampletime]

Ok, here's the follow up.....

i checked the ceiling rose and all was good. Decided to start tracing the wiring back to the consumer unit......luckily the first connection point was where the lighting circuit had been interrupted to feed the loft wiring. Pulled on a live wire and eureka, the conductor was broken and it pulled out out if the connection.

stripped back, re-terminated and re-connected.....

powered up and all was good.....

thanks to you all for your help and insightful tips....

 

[kme]

Thanks for letting us know. Glad you solved it

 

[Doc Hudson]

+1 to KME. Wherever possible I would encourage all members to try and add an update or conclusion post to any threads they have started, especially as in this case where it is an investigative Q&A problem. Thank you Smapletime.

Doc H.