smart51
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| posted on 28/8/10 at 05:24 PM |
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Odd electrical problem
The other night my bedroom light came on in the middle of the night. Switching the switch on and off made no difference so I removed the bulb and
went back to sleep. This is a bit inconvenient so I bought and fitted a new switch today and it made no difference, so I removed the switch and with
the wires bare, the light was still on. What is the problem likely to be?
There is a single twin and earth going to the switch so the ring main must be in the ceiling. What's going on in the roof?
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Stuart_B
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| posted on 28/8/10 at 05:33 PM |
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hi i would say that you have got a Permanent Supply at the light fitting, possible a cable has come out off the terminal and touch the switched side
off the fitting, or if an old house has bare terminal blocks and now the loop side is touching the switched side.
i would turn the lighting circuit off, and look at the fitting wiring, or if it is in the loft go up there look for joints.
hope that is some help
stuart
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RAYLEE29
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| posted on 28/8/10 at 05:55 PM |
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definately sounds like a problem in the rose
Ray
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smart51
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| posted on 28/8/10 at 05:56 PM |
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The ceiling rose has 3 twin and earths in it. All 3 lives go to a common point. 2 neutrals connect to the neutral of the light fitting and the other
neutral (with a red ring on it) connects to the live of the light fitting. All 3 earths are connected together. Nothing seems to be loose or shorting
together.
Edit to say, disconnecting the live feed to the switch makes the light go off and disconnecting the neutral with a red ring on it return from the
light both make the light go off. Am I right in thinking there must be a short in this length of twin and earth somewhere?
[Edited on 28-8-2010 by smart51]
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GeorgeM
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| posted on 28/8/10 at 06:05 PM |
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are there any mice in the loft??
My conscience is clear - I drive a GREEN car
MNR Racing
essexkitcarclub.com
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smart51
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| posted on 28/8/10 at 06:06 PM |
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quote:
Originally posted by GeorgeM
are there any mice in the loft??
If there are, do you think they are fried by now?
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MakeEverything
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| posted on 28/8/10 at 06:18 PM |
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quote:
Originally posted by smart51
The ceiling rose has 3 twin and earths in it. All 3 lives go to a common point. 2 neutrals connect to the neutral of the light fitting and the other
neutral (with a red ring on it) connects to the live of the light fitting. All 3 earths are connected together. Nothing seems to be loose or shorting
together.
Edit to say, disconnecting the live feed to the switch makes the light go off and disconnecting the neutral with a red ring on it return from the
light both make the light go off. Am I right in thinking there must be a short in this length of twin and earth somewhere?
[Edited on 28-8-2010 by smart51]
The "Neutral with a red ring" is a switched live. Be careful. If you mix all these up its a good hour or two to sort it all out - for a
sparks that is.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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omega 24 v6
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| posted on 28/8/10 at 07:24 PM |
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It could be the mice thing or the loose wire thing or the shorted out cable thing.
I have also seen in an old installation with steel conduit a scenario where the heat from the room caused condensation in the steel pipe ( in the cold
loft the other side of the insulation). rust formed and fell into the fitting douing the same thing as you describe.
If it looks wrong it probably is wrong.
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AndyO
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| posted on 28/8/10 at 10:04 PM |
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have you got a picture above the switch? nail through cable?
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FFTS
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| posted on 28/8/10 at 10:40 PM |
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All wrong...
It's definitely Poltegeist.
My friend had one in the loft and they love to play the permanent light on trick.
Chris.
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JoelP
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| posted on 29/8/10 at 08:40 AM |
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dont leave it on via the fault, its probably a poor link between the two that will be getting warm.
Multimeter from each end would tell you roughly where in the cable it is.
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smart51
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| posted on 29/8/10 at 01:06 PM |
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quote:
Originally posted by JoelP
Multimeter from each end would tell you roughly where in the cable it is.
Ooo! How does that work?
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JoelP
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| posted on 29/8/10 at 02:44 PM |
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mcb off and check its safe to work on. Then get the switch drop (the sleeved one), disconnect at both ends. Measure continuity between the red and
black conductor from at each end. With no fault there should be no conductance at all (ie high resistance). Your fault implies a link somewhere
between them. You are measuring up one leg, through the link and back down the other. The lower reading indicates which end the link is nearer to, and
the difference between the readings is an indication of how far from the middle it is.
tbh though im not sure how a randomly appearing fault like this would be caused, as mice nibble insulation, they dont tend to link conductors
together. Would deffo check the cable in the loft, and make sure no picture hooks etc have been fitted recently.
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smart51
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| posted on 30/8/10 at 10:55 AM |
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I took the loft boards up today and immediately found the problem. The metal conduit up from the switch was higher than the rafters so the boards
were pressing the cable into the metal and had cut through the insulation. A new length of twin and earth and its all working again. We've
been here for 10 years so the insulation has stood up quite well considering.
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omega 24 v6
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| posted on 30/8/10 at 11:51 AM |
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Erm the conduit should be earthed??? it'd the have blown the fuse.
Scenario where you go into the loft and grab the now live conduit is not a good one.
If it looks wrong it probably is wrong.
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smart51
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| posted on 30/8/10 at 12:57 PM |
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That's a good point actually. I trimmed the conduit back so that the floor boards cover it without pinching the cable but they should be
earthed and clearly they are not. I'll have to get on to that.
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JoelP
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| posted on 30/8/10 at 07:28 PM |
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generally the conduit doesnt have to be earthed as its not exposed, metal capping too doesnt need earthing. The terminal screws will often be the only
exposed metal part of the drop, and these are earthed via the earth connection in the backbox. The conduit and cable should be fitted so that it
doesnt pinch or chaff.
That said, earthing is probably a good idea.
Its a trade off against plastic conduit which doesnt conduct but also doesnt provide as much mechanical protection.
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omega 24 v6
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| posted on 30/8/10 at 08:54 PM |
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quote:
these are earthed via the earth connection in the backbox.
Obviously not in this case and IMHO not in many more that I have seen. Another big problem is plumbers who cut into copper pipe and then use plastic
fittings. They very often dont bridge the two copper ends again.
If it looks wrong it probably is wrong.
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