3 core and earth - all wires are live - WEIRD!?

[benjiman]

Hello chaps.

Im connecting up a lighting loop to a garage CU.

I didnt have any 2 core and earth left from the house installation. So used the reel of 3 core and earth instead. And simply terminate the extra (yellow) core.

Anyways, I connected it up to the CU, as you do

Lighting everythibng working.

So I carry out some basic tests. To my SHOCK I fond that the yellow core which I was going to terminate with insulation tape in infact live!?

Tested with the tester and there seems to be a small amount of current flowing through it. Not as much as the actual live though, as the light is dimmer.

I then disconected everything and simply connected NEW cable at the consumer unit, without further connections. (I though cable may be faulty)

After replacing with new 3 core cable, I tested the cores again. I took the cable live by connecting the red to the live terminal.

I then tested the yellow core and it was still live. Then I tried testing neutral and it was live as well!!?? What the heck is going on??!

Its beyond me! Surely this shhould not be possible. I strippid the entire leght of cable to see if there was a tear which may be connecting them.

Has anybody seen anything like this before?

 

[securespark]

There have been many posts like this before - try a search.

The live may be induced - what voltage reading between the phase conductors and cpc do you get?

Ie set up MM to read 240VAC.
Fit term blocks to stripped ends.
Put probes on these conductors in turn: Red + earth, Blue + earth, Yellow + earth.

Record the voltages shown on the meter.

 

[benjiman]

Cheers m8. Sorry didnt know what exactly to search.

Thanks.

Everything does seem to point towards the live being induced.

The socket side however is fine it seems. using 2 core and earth for that, and nothing is live which isnt supposed to be.

Gonna do a few searches on induced live, cheers!

 

[securespark]

You said you'd tested with the tester. What did you find?

 

[BJS_Spark]

What type of 'tester' are you using??

 

[benjiman]

I tested with a neon crewdriver tester. I found it lit up brighter when I tested live, but was less brighter when testing earth and neutral.

Off to whip out the old multimeter. Ive lost the manual. If I cant figure out how to use it, I hope you kind chappies can give my some tips

 

[andy]

I tested with a neon crewdriver tester.

get a multimeter. if you dont know how to use it, try it first with batteries and dead circuits

 

[jtaunton]

Do like SecureSpark says above with the terminal block.

Make sure its set to AC

Make sure its set to volts

make sure the voltage range is set to something higher than 240V

Measure the voltage between Neutral and Live, Earth & Neutral, Earth & Yellow.

If measuring between neutral and live doesn't give about 220-240 V then something's up with the multimeter.

If the earth-neutral and earth-yellow readings are about 30-50 V then it probably is induction and nothing to worry about.

 

[benjiman]

I tested with a neon crewdriver tester.

get a multimeter. if you dont know how to use it, try it first with batteries and dead circuits

Ive got a Gunson's Pocketmeter 1.

This is a multimeter right?

 

[jtaunton]

Right.

Turn the selector switch to the 500 on the blue V~ section

And be careful.

Edit - Sorry that bit about blue was for the pocketmeter 2. Turn it to any number bigger than 240 on the V~ range (can't find a big enough picture of one to advise any better than that - sorry)

 

[benjiman]

Ok sorry another quick question.

Just come back after doing some more investigating. When the all cores were live the earth was not actually connected to the earth bar in the CU.

After connecting the the earth to the earth bar in the CU, I tested earth and Neutral and they appear to be NOT live with the screw driver tester.

However I then tested the yellow core and it seems to still be live.

Should I earth the yello core at the CU? Will this stop it being live. I have chopped it off at the other points and terminated with insulatiion tape as I thought it wont be required.

Is it recomended to earth the unused core?

 

[benjiman]

Right.

Turn the selector switch to the 500 on the blue V~ section

And be careful.

Edit - Sorry that bit about blue was for the pocketmeter 2. Turn it to any number bigger than 240 on the V~ range (can't find a big enough picture of one to advise any better than that - sorry)

yup done that, now whats next?

750 is the biggest on the V~ side. Then the next smallest is 200. So i guess 750 is right.

Is says HV 000 on the lcd, and the - sign is flashing.

 

[benjiman]

Ok, we have some results chaps!!

Connected terminal blocks to all stipped ends, heres the result:

Live and Neutral = 249
Live and earth = 249
Live and yellow core = 0

yellow and eath = 250
Neutral and earth = 0
Red and Neutral = 250.

What do we make of them chaps?

Also does it matter which probes are made to do the testing? Ie red and black, which goes where?

 

[BJS_Spark]

I thought the old neon screwdriver was the offending test gear as this will show up induced voltage due to unterminated wires. It doesn't take much current to light the neon hence you don't get much of a shock when using the rubbish things.

Ground one end of the yellow to earth and it will go.

 

[kevplumb]

yellow and eath = 250

that dont sound right (well not to a plumber )