Baffled - Earth reading live

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Guys

I'm baffled - Scenario - Junction box with 4 cables - Main feed, Switched T/E, Cable from switched live/neutral to Light, Feed to FCU for seperate outside light.
The cable to the FCU is LSF cable.
The cable to the light is LSF cable.
Other cables grey pvc.
Why LSF? My customer wanted white cable and I couldn't get pvc in white.

By chance I tested the earth cable to the FCU - LIVE!!
Checked the JB. All connections correct.
Earth connection in the JB is live.
I can see the whole length of the LSF cable and there is no damage.

Switch cable goes intothe wall and has been plastered in.
Grey Cable to the switch - both conductors live (without the switch connected)

JB checked and is cabled correctly. No other feed to the circuit.

Why is the earth reading live both with a neon tester and a volt stick?
Why is the switch cable live at both conductors at the switch end and when live feed is connected - live at the JB end with no switch to make cinnection?
 
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Thanks for the replies guys

The Volt Stick is a basic Fluke bleeper and flasher so no it isn't reading a voltage.
I'm testing with my multimeter and installtest tomorrow. I didn't have them handy today.
(All left disconnected tonight by the way!)

The earth is definitely not connected to anything other than earth.

Could induced voltage pick up enough current to light up a neon or volt stick?

If it is induced voltage what is the answer?
Can it be so low as to noot cause a problem or is it more complex than that?

Why would the LSF cable be reading charge on the cpc when I can see the whole length of the cable, nothing is connected wrongly to it and it would appear not to be damaged?

This is a spooky one for me!
 
Like folk have said, it could be an induced voltage. The fact that the cpc is floating means it could well throw up a phantom voltage. Ground it effectively, and this will disappear. You'll probably find when you get the alphatek on it, it;ll be phantom, anyway.
 
stick a domestic bulb between it and neutral, that will drain off any induced voltage and show it isnt realy a phase conductor (or show that it is :eek: ) then you can ground it properly.
 
Just do an EFLI test on circuit that'll show up any earth problem
 
Desi

The volt stick could be picking up voltage from other wires if the are close enough so i do not trust them unless I can seperate the cores.

What voltages do you get between L-E, N-E, L-n?

What is the earthing arraingements for this instalation?
 
Hi guys

Some great feedback.
Grounding the earth did the trick. The fittings were metallic and were earthed to the covers only. I have earthed to the back box as well and this appears to have sorted it.

The meter was showing 25 volts L-E and 19 N-E. L-N was 243 as expected.

What causes this problem? This is the first time I have come across it.

"Induced" would indicate a transfer between cables despite insulation. Is this a magnetic ffect or something else?
 
Desie said:
Grounding the earth did the trick. The fittings were metallic and were earthed to the covers only. I have earthed to the back box as well and this appears to have sorted it.
can you clarify what you have done to ground it? have you simply connected to the backbox (aswell as the faceplate) or have you sorted the problem out at the other end aswell, because it sounds to me like its not connected properly at the other end either.
 
Desie said:
Hi guys

"Induced" would indicate a transfer between cables despite insulation. Is this a magnetic ffect or something else?


Mainly magnetic if an AC current is flowing in one wire. The changing magnetic field around the current carrying wire will induce a current in any adjacent wire. In effect a transformer with a single turn of infinate diameter ( a straight wire ) and no core so very in-efficient but enough to affect a high impedance meter to show a voltage.

If no current is flowing there is no magnetic field and capacitive coupling creates a voltage in the adjacent wire.

Bernard
Sharnbrook
UK
 

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