Voltage on the Earth cable for light circuits

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YogiM

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Hi

Testing PIR at the weekend. Doing R2 testing on light circuits, there was no continuity, meter read 81Vac on the screws and on the Earth leads. Tried to break down the circuits, but problem is still there. Tried to isolate the light circuits, but the person who did the wiring linked all the circuits together, but connected 3 light circuits to 3 separate MCBs.

The house is TNS = 0.17. 6mm main bonding.

Currently i have not issued a cert. still fault finding when i go there sometime this week. Removed the Earth leads off the metal back box onto choc connectors.

Suggested changing consumer unit, because it has old Wylex board BS3871with 60898 type 2 MCBs. Don't want to spend extra money.

Any idea how to solve this problem, also the place just had new laminated flooring put in last week.

Cheers

 
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Hi YogiM

Just trying to get a better idea of the problem mate.( not saying I can solve it from here, but I'm sure we can have a go).

81 V ac is that Live to earth and at all accessories?

Are you using long wander lead method then for R2 testing?

Do all the lights work properly or are some of the lamps glowing dimly (wired in series?)

How are the lighting circuits linked together?

 

Mr Sworld

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First off Yogi. You poor, poor sod! Bet you wish you'd never said yes to the job!

Ok, that's out of the way. ;)

So all the wiring is interconnected and all three mcb's have to be off to isolate all the lighting?

If so it's got to be at least a semi-rewire surely? And those laminated floors are going to have to come up unless you are very, very lucky and the interconnections between the circuits are accessable.

Which they won't be....... :_|

 

Admin1

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Welcome to the forum YogiM.

Lol @ Mr S's reason for editing his post.

 

YogiM

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Yes i am doing a wander lead method, because the property is on 3 floors.

All the light circuit works, no dimming of lights.

The previous boggers had put a cable for 2 way switching, but no supply.

81Vac seems to be Earth to Neutral, but i have to check.

when you switch off down stairs of one part of first floor works. When you switch off first floor, one part of 2nd floor works and the porch light works. When you switch off 2nd floor, one part 1st floor works. confused same ere.

 

Mr Sworld

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Bet you've got shared neutrals all over the place! Could explain the voltage between earth and neutral?

 
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Are you really really really sure the voltage is there, or is it induced because of the disconnected earth ?????? You probably tested it with a electronic meter. Put a bulb between earth and neutral and see if it lights.

PS, I thought a bogger was something you blew out your nose !!

 

ABC Technical

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Sounds like a right dogs dinner mate, I dont envy you over the next few days/weeks.

Good luck to you.

 

extension15

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81V, seems a little high for an induced Voltage...

Up to 30V I've seen, beyond that (unless a very large installation, with lot's of cables running alongside each other), almost certainly a fault of some description..

:D

 

davetheglitz

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It is surprising how high the induced/capacitively coupled voltages can be. Has anyone had the flashing of low energy bulbs on two way switching circuits where there is capacitive coupling to the switched line? The strike voltage must be around the 80v mark - just by coupling. Scares the willies out of poor old dears!!!

Nowadays we tend to use high impedance measuring instruments - going back in time we had our AVO's which may not have even registered the problem. S and S's advice is a goodun!

If you haven't got earth continuity to all the lights it's worth checking out the Electrical Safety Council Best Practice Guides on CU's for lighting circuits with no earth - http://www.electricalsafetycouncil.org.uk/bestpracticeguides.html

It isn't necessarily a rewire to fix it!

Good luck - and welcome to the forum - it's a damn good place to get advice without abuse - and long may it continue!

 
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If you have energy saving lams installed you may find voltage in the neutral when the lamps are switched off.

Have found 55V present on sitching circuits.

 

Mr Sworld

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Thinking about this a little more.

If the lighting is in such a shoddy state then you could well have old wiring without earths somewhere. Or the earths have just been twisted together and then loosened off over time.

So they are no longer referenced to the MET earth and now 'float' at the measured voltage.

 

Admin1

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Good luck - and welcome to the forum - it's a damn good place to get advice without abuse - and long may it continue!
:x

 
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--------------------------------------------------------------------------------

Yes i am doing a wander lead method, because the property is on 3 floors.

Wouldnt it be easier to do r1 + r2 method if property on 3 floors? Will also prove polarity by linking phase + cpc in cons unit.

Doing R2 testing on light circuits, there was no continuity

Presume then no continuityy of cpc so shouldnt you sort this out before doing live tests?

Not trying to be picky mate just thinking that doing the tests in order and sorting any probs as you go before supply back on.

Have you tested for borrowed neutrals?

Dont know what others on here may think but if its only 2 circuits sharing the neutral and the loading is ok then put the 2 phase conductors in the one circuit breaker and the 2 shared neutrals in the same termintion on the neutral bar.

 

jckent

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Are any of the switchs dimmer switches. I have seen high Vs on these

 
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(i.)

Doing R2 testing on light circuits, there was no continuity,

(ii.)

meter read 81Vac on the screws and on the Earth leads.

(iii.)

Tried to break down the circuits, but problem is still there.

(iv.)

Tried to isolate the light circuits, but the person who did the wiring linked all the circuits together,

(v.)

but connected 3 light circuits to 3 separate MCBs.

(vi.)

Removed the Earth leads off the metal back box onto choc connectors.

(vii.)

doing a wander lead method, because the property is on 3 floors.

(viii.)

All the light circuit works, no dimming of lights.

(ix.)

The previous boggers had put a cable for 2 way switching, but no supply.

(x.)

81Vac seems to be Earth to Neutral, but i have to check.

(xi.)

when you switch off down stairs of one part of first floor works.

When you switch off first floor, one part of 2nd floor works and the porch light works.

When you switch off 2nd floor, one part 1st floor works. confused same ere.
Hi Yogi M .. welcome m8! :D

Just tryin to get me head round the facts here and chuck out the red herrings, so I labelled a few of your points for ease of reference?

Just want to see if I have got me facts straight?

Q1) 're v.' There are three lighting circuits are they PVC T&E or singles..

Q1b) If singles are you sure you have the right pairs? L & N ?

Q2) 're i.' Is the earth continuity missing off ALL of the circuits or just one?

Q3) 're ii.' Is the voltage on back box on ALL switches on ALL circuits or just some...

Q3b) If on several does it stay constant all all points tested.

Q3c) Is the voltage present with all switches OFF and bulbs out?

Q3d) When you get the voltage are ALL of the lighting circuits switched OFF at CU?

Q4) 're i.' You say there is no low resistance continuity... what about a high resistance continuity.. e.g. do Ins res @ 250v from wander lead to earths?

Q5) 're iv.' Joined all the circuits together? do you mean the neutrals are all combined ("borrowed") between each other.?

Q6) 're xi.' Obviously the circuits have a non-logical arrangement. Have tried to verify which bits are actually joined together? say with an insulation resistance test between the individual conductors of the circuits with the conductors of the other two light circuits? e.g. 'L' cct1 to 'L'cct2 & cct3 etc..

Q7) Are the lighting circuits looped in and out at Ceiling rose / Switches / or J-box somewhere?

Q8) Are the cpc properly sheathed? or are they bare.. could there be a cpc touchin a live part... & with no (or high res) no fuse blow volt dropped across CPC??

Blimey!!! :( its like sitting a ruddy exam! :eek: :O

Me brains stoppin now......

need to recharge batteries:^O

Any way these are a few of the points I would want to try and verify to help get me working in the right direction..

This is a job you need to go round with a notepad & pen.. ;)

write down what you test & values you get...

or you will end up chasin your tail. :_|

SL best of luck m8:D

 

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