Stray Voltage On The Cpc.

[safedepth]

More advice sought please.

During testing yesterday I found 80 volts on the cpc of a socket ring with respect to earth and neutral.

TT installation. Ze, tested using multimeter was 92 ohms.

Ring continuity was correct,

r1r2 was correct,

IR was clear at 299M.

All items were unplugged, 3 items on fused spurs, all disconnected.

All sockets removed from walls, no indication of any problem.

RCD on circuit, 30mA tested correct.

The only thing we could find that gave any hint was all cables from this board, ( a 15 year old single RCD board fitted as part of an extension), were bunched together passing through the wall from old to new building.

All tested with a Megger 1552.

Could 80 volts be generated by self induction?

Any ideas.

Incidentally, I rang the NIC tech help line who couldn't. (Help that is)!

 

[SPECIAL LOCATION]

More advice sought please.

During testing yesterday I found 80 volts on the cpc of a socket ring with respect to earth and neutral.

Any ideas.

Incidentally, I rang the NIC tech help line who couldn't. (Help that is)!

So your CPC is open circuit to everything else when you did this test?

its basically a long aerial wire running around the installation picking up whatever happens to be available to induce...

Why were you testing it in the first place????

try connecting the CPC to earth..

you say it is 80v with respect to earth...

so if it is 80v and you make a negligible resistance connection between CPC & earth  say 0.1 ohms..

you will either get a big bang due to 80v/0.1ohms = 800Amps....

Of the induced voltage will diassapear...

My bet is the second option!!!

What meter were you using to read this "voltage"?

 

[ProDave]

Do you REALLY mean you tested Ze with a multimeter?

What "correct" reading did you get for R1+R2 on the ring final?

Try measuring R1 AND R2 separately and tell us the readings.

I would suggest your CPC is floating and not connected anywhere, but your R2 reading would confirm that.

 

[safedepth]

Spec Loc,

So your CPC is open circuit to everything else when you did this test?

Yes. IR tests all clear at >299 to line and neutral.

its basically a long aerial wire running around the installation picking up whatever happens to be available to induce...

Why were you testing it in the first place????

This board is split via henleys from the houses first board. The first board contains the MET. Whilst testing bonding on the first board I disconnected a 10mm Green and Yellow expecting it to be the water bond, using a wander lead to prove it was that I got a voltage reading of 80v, showing something else. Further inspection showed it to be the Earthing Conductor to the second board.

try connecting the CPC to earth..

I did, then of course the voltage disappears to earth, which is what it had been doing until I disconnected it.

you say it is 80v with respect to earth...

so if it is 80v and you make a negligible resistance connection between CPC & earth  say 0.1 ohms..

you will either get a big bang due to 80v/0.1ohms = 800Amps....

Of the induced voltage will diassapear...

My bet is the second option!!!

You are right. As I siad we are assuming it is an induced voltage because of the testing we have carried out, I have not seen such I high induced voltage.

What meter were you using to read this "voltage"?

Megger 1552.

Cue all of the comments about how rubbish they are

Do you REALLY mean you tested Ze with a multimeter?

Yes, well MFT, Megger 1552

What "correct" reading did you get for R1+R2 on the ring final?

Generally 0.4 ohms but up to 0.7 on a spur.

Try measuring R1 AND R2 separately and tell us the readings.

I would suggest your CPC is floating and not connected anywhere, but your R2 reading would confirm that.

This voltage is only present when disconnected from the earth bar in the board, (loath to call it a MET as that is strictly located in the first board).

When reconnected the voltage goes straight back to earth via the conductor and rod.

 

[NozSpark]

Your reply above just begs the question....

WHY DID YOU DISCONNECT AN EARTHING CONDUCTOR, OR BOND, OR WHATEVER, WITH THE SUPPLY STILL ENERGISED??????????

:shakehead

 

[ProDave]

So the CPC is floating when you disconnect the earth.  :shakehead

Why does that surprise you? :C

 

[kerching]

Your reply above just begs the question....

WHY DID YOU DISCONNECT AN EARTHING CONDUCTOR, OR BOND, OR WHATEVER, WITH THE SUPPLY STILL ENERGISED??????????

:shakehead

One of my ex employees tried that on a computer install job!.......it stopped him from considering doing it for a second time whilst the installation was "wick"!

just laughing

 

[safedepth]

Your reply above just begs the question....

WHY DID YOU DISCONNECT AN EARTHING CONDUCTOR, OR BOND, OR WHATEVER, WITH THE SUPPLY STILL ENERGISED??????????

:shakehead

Picture the scene.

Large ish house, 2 consumer units, one each end.

Supply comes in from meter cabinet to henley blocks. At this point it splits to the two boards. Earthing conductor comes in to the first board. As it turns out it then goes out to the second board. Also in this first board is the main bond to the water.

We are proving the water bond by disconnecting it and checking continuity with wander lead. When the probes are attached between the disconnected end at the board and the disconnected end at the stop cock we get a reading of 80 volts. We have inadvertantly disconnected the earthing conductor going to the second cu.

I.E. we are getting a reading of 80 volts from the new ish CU's earthing conductor. Further testing revealed it was on the ring on that board.

That's why. Not good I admit, possibly negligent because we didn't take care to confirm the supply to the 2nd board was off in case we did what we did. In defence the house was empty, only me and my colleague in there.

So the CPC is floating when you disconnect the earth.  :shakehead

Why does that surprise you? :C

What surprises me is the size of the induced(?) voltage in the cpc when disconnected.

I understand that had I not disconnected the earth conductor I would likely never have found this stray voltage. It may be that it has been present in many situations prior to this. Once I found it I was obliged to investigate. And on top of all this as I have not experienced this before I was concerned enough to enquire about it.

That is why I posted the original question.

Could 80 volts be generated by self induction?

 

[ProDave]

The trouble is, you originally asked why you were getting an induced voltage on the CPC when R1+R2 was "okay" which clearly does not make sense.

So why we all ponder what might be going on, you omit to tell us the CPC was only floating when you disconnected the earth. headbang

 

[Sidewinder]

What was the current in the "CPC"?...

 

[steptoe]

probably about a gnats above ZERO

and if he had checked with a proper meter the voltage would have been about the same,  :|

 

[safedepth]

The trouble is, you originally asked why you were getting an induced voltage on the CPC when R1+R2 was "okay" which clearly does not make sense.

So why we all ponder what might be going on, you omit to tell us the CPC was only floating when you disconnected the earth. headbang

I did say the voltage was with respect to earth. That does imply between the cpc and the earth. In which case the cpc must be disconnected from the earth. Why is that so hard to work out for you?R1r2 ws correct. As I said in the op the voltage is between the cpc and earth. Two separate things. I never claimed that it made sense. Indeed the lack of sense was part of the puzzle.

probably about a gnats above ZERO

and if he had checked with a proper meter the voltage would have been about the same, :|

Which meter?I assume from your previous posts you mean a fluke. Do you honestly believe that had I carried out this test with your fluke my readings would have been 80 volts less? Serious question.

If that is so why do so many people on here spend so much time praising the products of a certain forum sponsor yet would never use his products. Should my mft be banned from sale due to it being so carp?

 

[Sidewinder]

Safedepth,

You need to understand the way that an MFT, any MFT measures voltage, it presents a VERY high impedance source.

To eliminate induced or stray voltage you need a LOW impedance source.

An MFT is not a suitable tool for this sort of diagnostic work.

 

[steptoe]

I did say the voltage was with respect to earth. That does imply between the cpc and the earth. In which case the cpc must be disconnected from the earth. Why is that so hard to work out for you?

R1r2 ws correct. As I said in the op the voltage is between the cpc and earth. Two separate things.

Which meter?

I assume from your previous posts you mean a fluke. Do you honestly believe that had I carried out this test with your fluke my readings would have been 80 volts less? Serious question.

If that is so why do so many people on here spend so much time praising the products of a certain forum sponsor yet would never use his products. Should my mft be banned from sale due to it being so carp?

1  yes, and I'll bet you didnt test to earth, you tested to the incoming CPC, not earth,

2 NO, actually I meant a proper analogue meter

3 yes, they should still be banned IMHO, I think they are like so many other products out there and living on a name, the only reason so many people use megger is that is what the short course tutors push as they get comission from megger, and most of the people on short courses dont actually know how to test, they only know what buttons to push on a megger to get certain test results.

TBH, this thread should be in the DIY forum, or at best, student section, nobody charging for their services should be asking downright idiotic questions like this.

BTW,

I dont use a fluke,

I have an HT 5058 [i think it is]

 

[safedepth]

1 yes, and I'll bet you didnt test to earth, you tested to the incoming CPC, not earth,

Bloody fool read it properly. I tested between the cpc and the earthing conductor.

2 NO, actually I meant a proper analogue meter

Which analogue tester do you use. I was originally trained on an AVO 7 if I remember correctly, it was 25 years ago. Maybe AVO 8.

3 yes, they should still be banned IMHO, I think they are like so many other products out there and living on a name, the only reason so many people use megger is that is what the short course tutors push as they get comission from megger, and most of the people on short courses dont actually know how to test, they only know what buttons to push on a megger to get certain test results.

TBH, this thread should be in the DIY forum, or at best, student section, nobody charging for their services should be asking downright idiotic questions like this.

The idiotic bit being what. That I found something I had not previously experienced? That I found something not previously experienced by my scams technical helpline? Or that I found something you have so far not been bothered to attempt a civilised answer to.

BTW,

I dont use a fluke,

I have an HT 5058 [i think it is]

 

[NozSpark]

Steps,,, you do know that I have a Megger don't you!

 

[steptoe]

Steps,,, you do know that I have a Megger don't you!

Yes.

Do you know what button to push?

I did.say most.

I know a spark of 30years that has one, still doesnt make them any good imo.

 

[NozSpark]

I know you said MOST.... only messing

TBH though (and I've said this before) I find my Megger 1502 very easy to use and when I've had a go of a Fluke I didn't like the menu driven function selection.... But in all honesty I can't remember why I bought it over a Fluke at the time

 

[steptoe]

@outofhisdepth

NO, what one of your inconsistent posts did you say earthing conductor?

OP is to earth, as are others,

Get basics right then answers may be more constructive.

You didnt find anything, apart from the fact that your short course left you short on actual.competence.

I may be an idiot, but at least Im.competent enough to actually be working as a spark,

not simply masquerading as one after having wasted my life doing something else,

I wasted mine drinking beer and learning a trade.

 

[kerching]

Ht5058 eh!

i am just about to order a Fluke 1654 from MM as my old tester is looking a bit grubby!

but now you've got me thinking......HT 5058 eh....

...http://www.alibaba.com/product-gs/619217768/Summer_straw_fedora_flower_hat_HT.html

NICE