Discuss QUERY - Potential LNE fault - Lighting in the Electrical Forum area at ElectriciansForums.net

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overskilled

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So on one bedroom light in a clients home, Switch off at the pendant L-> N = 30Volts, L->E = 108-110Volts, N->E=244Volts

Checked the main lighting junction box and everything is wired ok there, though this bedroom only still reads 110V L-E (RCD doesn't trip either)

Slightly strangely the light switch for this bedroom and the adjoining bedroom are fed via 3 Core and Earth

So before I rip up the attic floor and replace the junction box to light fixture cable run along with running 2 separate T+E's to the switch, am I right in thinking there could be a nail or similar through the light power supply cable somewhere in its run?

Any other possibilities?

(other lights on the same circuit read as they should (off All 0, On L-N 244, N-E 0)
 

daveelectrician

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Sounds like a borrowed neutral to me. Could try knocking each light off in the house 1 by 1 until it reads 0 volts, or 2 neutrals from 2 circuits connected together in a switch
 
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overskilled

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All the upstairs lights are supplied from one main junction enclosure, neutrals all joined together, perm lives together, and switched lives from switches to lives on light fixture cables that run direct to the light fittings.

Checked another light fixture and it doesn't have the same issues

Only thing I can think of is that this one light is 2 lengths of cable joined somewhere under the floor somewhere badly or damage to the cable somewhere.I'm going to check the other light fixture fed off the 3+E switch feed cable tomorrow to rule it out.

The 3+E supplies red permanent live to the common on switch one, red strapper wire from common through wall to switch 2, blue from switch 2 L1 to light 2 supply cable red live core, yellow core from switch 1 L1 to light 1 supply cable red live core.
 
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overskilled

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Reason for call: Owner (relative of mine) got a belt off the light fixture when changing the pendant to a different fitting when the light switch was off (switched feeds only to the pendant connections, all the permanent lives are in an enclosure elsewhere in the attic). At the time, I thought that perhaps the L and N were switched at the junction point (therefore the switch was switching the neutral not the live, did a quick visit on the way home, voltage tester indicated voltage at the neutral but not at the live, so made arrangements to rectify while they are away on holiday.

Cracked open the junction enclosure and no crossed connections and no joins from other circuits either. Remade the earth connections and checked all the connections were tight.

Not done the IR testing yet as my IR tester needs replaced (Been off the tools for a while, getting back into it and now need to re-buy some testing kit)

House was rewired last back in 1988 but the wiring was tested by another contractor after a CU change about 2 years ago, No PIR done though as far as I'm aware, just the testing, I'll dig out the figures, though they might be falsified for all I know.

Been told that owner got a belt several years ago from the same light fitting, but the fault wasn't repaired ("the light still comes on" excuse), so its been lingering around for a while.
 
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overskilled

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fair enough point, however the neutral for the light is connected to the same bundle of neutrals as all the other lights (none of which that I've tested exhibit this fault) Its solely this one light it seems.
the MCB for the lighting circuit isolates this light (and all the others on the same lighting circuit), however the light switch for this one room doesn't.
I'm going to lift the attic floor and make sure there isn't a join lurking under the floorboards or any other weirdness.
Its not a long run, so I might just recable this fixture and see if that eliminates the fault (very least it would cover insulation breakdown and then I know for sure that there are no joins or nails etc penetrating the cable...I have some cable sitting thats too short for anything else tbh.)
Thanks for the help guys, appreciated.
 

Guitarist

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Not done the IR testing yet as my IR tester needs replaced (Been off the tools for a while, getting back into it and now need to re-buy some testing kit)
Go and treat yourself to some test gear, then you will be able to fully test the circuits. Hard to fault-find without proper equipment.
 
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overskilled

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Will do as soon as I get back to work proper (Sadly signed off at the moment due to a nagging injury)
Have a wander round the wholesalers at some point and see whats interesting and tempting....oh and time saving
 
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overskilled

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Any advice on anything to avoid testing equipment wise? Salesmen are always good at glossing over bad points etc.
Considering a Megger MFT1710 or 1720, but the price on the 1720 is making the bank balance wince a bit, depends on how much time it would save etc I suppose.
 
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overskilled

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:p "I'm leaving" (yeah breakups are so much fun) then I fell when walking the dog to calm down and did my ankle in.....again, flipping murder climbing the attic ladder today.
 

Guitarist

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It may be prudent in this case (considering the lack of test gear and your injury) to get an electrician in.
 
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overskilled

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Take your point on advisory.
To put it mildly, a rather noticeable percentage of other electricians in my rural area are.....cowboys.....judging from the messes I've had to sort out in this house alone (different jobs done by different approved sparks and none of them done properly, corners cut all over the place)
I'll get some test kit sorted, the ankle I can cope with as long as I'm not up and down ladders all day long its alright.
 

Guitarist

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Take your point on advisory.
To put it mildly, a rather noticeable percentage of other electricians in my rural area are.....cowboys.....judging from the messes I've had to sort out in this house alone (different jobs done by different approved sparks and none of them done properly, corners cut all over the place)
I'll get some test kit sorted, the ankle I can cope with as long as I'm not up and down ladders all day long its alright.
I wish you all the best then.
 
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MarkieSparkie

Any advice on anything to avoid testing equipment wise? Salesmen are always good at glossing over bad points etc.
Considering a Megger MFT1710 or 1720, but the price on the 1720 is making the bank balance wince a bit, depends on how much time it would save etc I suppose.
Either Megger is sound choice. Ensure your purchase comes with the latest firmware, this is vital. You need firmware version 2.01 or later (current version 2.05) for the best measurement stability. 2 wire loop test is still a bit of a novelty and its use, is at best unpredictable at the moment, but with each firmware iteration its getting better. 3 wire loop testing however is accurate and predictable, so use this where ever possible.
The R1+R2 function is just a sales gimmick and it's use encourages the worst testing practices of the industry cowboys, and is therefore best ignored. Test-meter our forum sponsor sell Megger and offers 5% discount to forum members, they can also be relied upon to ensure that you get a Megger MFT with the latest specification firmware, but there is no harm in specifying this requirement when placing your order just so there can be no doubt.

Electricians Forums in association with test-meter.co.uk
 
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