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Earth / Neutral fault on Lighting Circuit


 
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Jay2008

from United Kingdom

Joined: 07 Dec 2008
Posts: 4
Location: Kent,
United Kingdom

PostPosted: Sun Dec 07, 2008 3:09 pm Reply with quote

This is my first post on this forum ..... so here goes.

I moved to a house which had cables for wall lights already in place, but no actual lights. Just a couple of live cables pointing out the wall.

These are stair lights controlled by a switch at the bottom of the stairs, and a switch at the top.

Bottom of stairs switch is 3 gang / 2 way switch. (Other two lights are single lights)

Top of stairs switch is 1 gang / 2 way switch

Along with some other essential electrical work (installing the correct Earth bonding to gas & water) I had an electrician fit some LED lights. Each light has a bank of 9 white LED's.

After a couple of days I noticed that the lights did not quite turn all the way off - there was a faint glow. I phoned the electrician who unhelpfully said "You have a Neutral to Earth fault ..... you need to find your junction box" ... and hung up.

I left the lights in place and learned to live with the fault as I couldn't find the junction box.

1 year on and during some decorating I discovered that behind the light front, most of the LED's have blown.

I ripped down the ceiling in my hallway to find the junction box, which was a mess. I had a different electrician in to diagnose the problem.

He removed the neutrals from both lights to the junction box .... but the lights were still faintly illuminated.

He confirmed an Earth to Neutral fault. He also told me he has a similar problem at home, and has had shocks from his lights switches for 11 years !!!!!!!!!!!!!!!!

I want to actually fix this fault, rather than ignore it like the two electricians.

How can I go about this?

Is there an electrical tester that will pinpoint how far away the fault is?

The house has a new-ish Consumer Unit with MCB's. The circuit is the correct amperage (6 amps) for a lighting circuit.

Some of the cabling is over cabled ..... but none appears to be under cabled.

Is this a common problem ..... is this just an issue for LED's ?

I'm okay with logical fault finding (IT Network background) ... but am far from a competent electrician.


Any suggestions on where to start - is there an easy way to diagnose this ... or will I have to disconnect each room to find the logical path of the circuit.

Any help greatly accepted.

Jay.
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experience

from United Kingdom

Joined: 23 Feb 2008
Posts: 91
Location: United Kingdom
Thanked: 4 times

PostPosted: Sun Dec 07, 2008 6:12 pm Reply with quote

Any good spark should be able to find this- although it can take time depending on the size of the circuit.
Is this on the upstairs or downstairs lighting circuit? If upstairs get yourself in the loft and look for some JB's. Likewise if on the downstairs lights see if you can trace the wiring by popping a few floorboards up close to the light fittings. With the circuit isolated open any found JBs and check to see that all the wires are where they should be and are not loose. Same at light switches and light fittings, check all connections.
What happened to the 2 live cables hanging out of the wall - have they been properly isolated?
Apart from that you need to get a spark in whos got a tester, he can carry out insulation resistance tests on the lighting circuit and "split" the lighting radial up into sections to locate the fault.
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333rocky333

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Joined: 12 Jan 2008
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Location: Essex,
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PostPosted: Sun Dec 07, 2008 6:41 pm Reply with quote

Bit confused here.

How can a N to E fault make the Led's glow when there switched off icon_question.gif
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Jay2008

from United Kingdom

Joined: 07 Dec 2008
Posts: 4
Location: Kent,
United Kingdom

PostPosted: Sun Dec 07, 2008 7:27 pm Reply with quote

Thanks for the replies.

Here's the info you asked for.

There is only one lighting circuit - my house is small enough to only need one.

I have another 6 amp circuit ... however I have switched this off as it doesn't seem to do anything. Nothing stops working when it is set to off at the MCB. Turning it on does not affect the LED's glowing.

The two live cables are where the lights are now fitted. They had a piece of insulation tape wrapped rather poorly round them when I got here.

By 'live cables' I mean a set of 3 cables terminated in a block. Both blocks had live and neutral tails coming out of them with the mentioned tape on them. Apologies for the confusion.

I've had three sparks in all have a look in the house ... none of them has mentioned a tester to find faults. The advice from the last guy was actually try some different lamps to see if they could take the overflow voltage. I wish I was making this up.

Rocky ... as I understand it, when the neutral wires are disconnected from the junction box a small current is still finding its way to the lights via another route ... this is the whole problem.

The live feed to the lights switch is to the switch at the top of the stairs. The two way light switch seems to be correctly cabled.

I have stuck my head in the loft and some of the JB's seem to be a bit on the old side. I'll have a go at re-connecting all the light switches and JB's that I can easily access and see if that solves the problem.

I've got a multimeter, but I'm not sure how to use it for diagnostics. I can check the voltage and I get 239~241 although mostly it sits on 240v.

I have a socket tester and all my sockets check out.

All the sockets are on radial circuits with surface mounted boxes ... I think my house was cabled by a really lazy bloke - very very little is chased in.

Thanks for the guidance.

If I still can't sort it, I'll ring round for a spark with the correct tester.

J.
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slup

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Location: Wiltshire,
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PostPosted: Sun Dec 07, 2008 7:44 pm Reply with quote

LED's and CFL's will often glow slightly due to capacitive or inductive coupling on the cables.

They only need a tiny amount of current to operate so your symptoms are not entirely unexpected.

Also, the cheaper LED lamps don't last very long at all - so to see that some of the LED's in the clusters have failed is again not hugely surprising.
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Jay2008

from United Kingdom

Joined: 07 Dec 2008
Posts: 4
Location: Kent,
United Kingdom

PostPosted: Sun Dec 07, 2008 9:07 pm Reply with quote

Thanks Slup and Experience,

The lights are these ones

http://www.searchlightelectric.com/modules/shop/view.asp?catid=4&Prodcode=9907WH

Is 20 a cheap lamp ?

One lamp had 8 out of 9 LED's go in about 1 year / 18 months, the other lamp has had 2 out of 9 go.

Is this normal. They are my only LED's so I have nothing to compare them to.

J.
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securespark

from United Kingdom

Joined: 11 Jan 2004
Posts: 24871
Location: Cheshire,
United Kingdom
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PostPosted: Sun Dec 07, 2008 11:45 pm Reply with quote

Just to confirm: Are these glowing lights controlled by two switches?

If so, that is almost certainly going to be due to a characteristic of the lamps, not a fault.

And, as rocky points out, I cannot see how an N/E fault can cause this problem.
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macca

from United Kingdom

Joined: 31 Jul 2004
Posts: 13
Location: United Kingdom

PostPosted: Mon Dec 08, 2008 1:22 am Reply with quote

This is quite common on LED & energy saving lamps when connected by 2 way switches. Apparently its something to do with the capacitance in the strapper wires (which connects the 2 switches) discharging through the landing light or in your case the LEDs, which can be enough to make a low energy light glow or flicker. I've also been told that it mainly happens when using cheaper light fittings - dont know how true that is though
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Jay2008

from United Kingdom

Joined: 07 Dec 2008
Posts: 4
Location: Kent,
United Kingdom

PostPosted: Mon Dec 08, 2008 9:11 am Reply with quote

Thanks Macca - I may review how I light this stairwell.

Thanks too to securespark ... I didn't get what Rocky meant earlier ... apologies to him.

J.
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aptsys

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Location: Cambridgeshire,
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PostPosted: Mon Dec 08, 2008 12:35 pm Reply with quote

The LEDs in these light fittings tend to be overdriven and have poor thermal characteristics which cause them to fail at an alarming rate. With proper thermal and electronic design the LEDs should last 100k hours.
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