Interesting Fault.

[securespark]

Hi Folks!

Went to a house today to investigate a fault. I have to say that I was called away and have to return, so I have not investigated further yet, sorry!

It was two bedroom SES fittings, three 40W lamps on each. They are switched via one 1G1W switch.

The lady was complaining that on switch off, a slight glow was emitted from the lamps.

Initially, I could not replicate the fault.

However, upon leaving the lights on a few minutes, I found that upon switch off, instead of the voltage falling away to zero (or thereabouts), it dropped to 48V.

I found the longer the switch was left on, the longer the residual voltage lingered, up to a maximum of around 10 seconds.

Then I removed all lamps and switched off after a few minutes. The voltage remained at 244V.

With one 40W lamp in circuit, the switched-off voltaged was 213V.

So I dropped the fittings to disconnect the switchwire in order to bell it out.

Strangely, there was both a loop in and out and a switchwire at both light fittings.


The IR between L & Sw L at the switch position with switchwires disconnected at the ceiling position is 0.001Mohm.

I had to leave, so left the switchwires disconnected and I will return in a couple of weeks.

An odd one.

Obviously there is some damage or a short of some kind on the switchwire, but more than that I cannot guess.

Any thoughts so far??

 

[holmslaw]

..

 

[securespark]

Considered that. Expand, if you will, my good fellow!

 

[Lectrician]

I would say a neutral & sw-live confused in a fitting elsewhere on the circuit, and the effects you describe caused by a high impedance type load on the circuit - TV booster, Shaver Point, something like that.

 

[bernardgreen]

If there is one switched live at each lamp and only one switched live at the switch then it seems there is a junction box somewhere in the loft. Probably at some time there were two switches, one per lamp.

My bet is that someone has taken a "feed" from that junction box for a TV aerial amplifier or similar very low power load.

Ask if the TV picture degrades when the bedroom light is on ( when the switch is closed the "power" to TV amp is shorted )

Other possible culprits could be a shaver point with a permanently on-line transformer, a clock socket ( if the clock has battery back up the loss of power would not be noticed ) mains powered smoke alarms

 

[dormermike]

Back in a couple of weeks and customer is happy to wait, lucky you! I wouldnt.

 

[securespark]

It's only one bedroom out of action, she is happy to manage with table lamps.

 

[securespark]

Ha, ha!!

Went back today.

What a c*ck-up!

Can't believe it....

Amazing that it ever worked!

Can't have been a qualified spark!

He wants stringing up...

What a shower!

 

[Alarm]

And as we are not mind readers.

Care to expand?

 

[securespark]

Oh, did I not mention it? Sorry!

 

[Alarm]

And again

I`ll go with Neutral and SW confused

 

[securespark]

Yeah.

It was an odd install because both light fittings were wired 3 plate with feeds in and out & a drop to the switch, but the two fittings came on together & there was only one switch and one switch cable at that switch.

In the loft was a switchwire dropping to the switch, connected to both switchwires from the fitting positions.

Then a fourth cable ran off to an outside light fitting, via a DTD photocell: http://www.tlc-direct.co.uk/Products/TLPEC1000.html

All the reds were together & all blacks together. Just so happened that the fittings all had tungsten lamps fitted, so the switchwire was effectively a neutral when the bedroom lights were off. In other words, the DTD light would have operated as long as the bedroom lights were not on, but not when they were.

Just the remaining part of the puzzle to figure out now.

The lady said that only recently have the bedroom lights not been turning off properly. Surely it would have operated the same way since its installation?

Also, I'm trying to get my head round how the "residual" voltage on turn off was 230 with all lamps out (in the daytime) and when more lamps were added, the residual voltage got less and less. With all lamps in (6 x 40W), the residual voltage on switch off was 48V, dropping to zero after a few seconds. However, (this bit I understand) at night, the residual voltage did not drop off until sunrise: the customer complained that the lamps were glowing when she went to bed, but were not when she woke up. I guess because the photocell switched off at sunrise, hence the residual voltage fell away & the lamps stopped glowing.

EDITED ONLY FOR TYPO'S

 

[Alarm]

Probably been happening all the time, knowing liars-oops customers

 

[bernardgreen]

Probably been happening all the time, knowing liars-oops customers

Old ladies can become forgetful. Now where did I leave my tea ?

 

[Alarm]

Probably been happening all the time, knowing liars-oops customers

Old ladies can become forgetful. Now where did I leave my tea ?

In your nightie`s pocket