130 volts pd between live and earth TT system

coldelsol

Hi everyone
I have signed in here to see if anyone has experienced this, and found solution if there is one.
Voltage L to N 230 Volts Lto E 130 volts

my test meter will not work for earth loop imp. unless I do it the same way as the old two wire tester by bridgeing the N+E together which gives me 0.78ohm which is fine.the reason my meter will not work 3 wire LNE cause the voltage between Live +E is 130V , I thought this may be due to bad earth spike connection which I cant find .the over head pylon is 20mtr from house so I did an earth loop test at the supply meter mounted on pylon using the earth connection to the pylon thinking you wont get better than that and run a seperate wire connected from the pylon to MET in DB, guess what no difference at all. the ground here is major rock and thinking there may be no improvement on what the electric supplier has achieved when they connected there earth connection to ground.

voltage N to E 0v
Im assuming the polarity is right cause its over head main though its a Spanish installation and colour codes dont mean jack all to some.for all I know with not having a decent earth it could be N to earth voltage ?which is High and would understand why my meter not enable to read cause of exceeding 50v.which will not let me do an rccd time test either

ok now for me tablets where have I put them lol

meercat

sorry cant help
this has limited info
http://www.boards.ie/vbulletin/showthread.php?t=2056177254&highlight=spain

Bruthal

Just noticed you said your loop impedence tester is not working except when you bridge neutral-earth, then its almost certain the installation just has no earth connection at all, or at least the items you checked.

If you have a socket for example and the earth is wired back to the fuseboard earth bar, and the earth bar is connected to nothing, and you test between live and earth with a digital multi tester, you will usually get over 100v reading simply because of the very high impedence of a digital multimeter.

Anyone can try it, just test between live and the plasterboard wall and you will get a reading. So in the above installation there is just no earth where you tested, might be an earth wire at the socket, but it probably does not eventually connect to an earth rod.

Bruthal

coldelsol wrote: »

voltage N to E 0v
Im assuming the polarity is right cause its over head main though its a Spanish installation and colour codes dont mean jack all to some.for all I know with not having a decent earth it could be N to earth voltage ?which is High and would understand why my meter not enable to read cause of exceeding 50v.which will not let me do an rccd time test either

ok now for me tablets where have I put them lol

On an installation with no main earth connected to the earth bar you will get the above readings. Neutral to earth will read 0v once there is no earth leakage from any circuits. But live to earth will read less than the 230v if the earth being tested connects to nothing. If the impedence from the earth bar to earth is 1 megaohm(earth bar not connected to earth rod or neutral) as an example, and the multimeter impedence is 1 megaohm when set for voltage testing, then the reading from Live to Earth will be half of 230v or 115 volts.

This means that a reading significantly below 230v from live to earth with a digital multimeter means there is no actual main earth connection to an earth rod or neutralising connection.

It also means a poor earth connection, where for example the main earth bar is connected to an earth rod but the impedence for an example is 100 ohms, a digital multi tester will still read a full 230v.

These are reasons why proper testers like earth loop impedence testers are needed which are designed to acurately measure very low impedences.

M cebee

for TT with ADS via rcd i think your fault loop impedance should be up around 200ohm or more

as robbie said it sounds like there's a problem if your voltage tester is showing 130 L-E

not familiar- but for TT i'd prob switch off power and check external fault loop impedance

is spain TT ? and what's the rcd's trip currents

Bruthal

M cebee wrote: »

for TT with ADS via rcd i think your fault loop impedance should be up around 200ohm or more

as robbie said it sounds like there's a problem if your voltage tester is showing 130 L-E

not familiar- but for TT i'd prob switch off power and check external fault loop impedance

is spain TT ? and what's the rcd's trip currents

A digital multimeter testing between live and a socket earth terminal where the earth wire does not connect to anything will show a voltage more than zero.

Try testing between live and the end of a coil of cable, it wont be the 0v reading many would expect. A digital multimeter testing voltage is in series with the rest of the circuit, and the rest of the circuit would have to be a substantialy high impedence for the reading to be less than 230v, as in testing between a live and an earth connection that is not actually earthed will show a fair few volts.

As i said before, test from live to neutral with a 1 megohm resistor in series with the voltmeter and it may read over 100 volts, put in a 1kilo-ohm resistor instead of the 1 meg one and the reading will be the full 230v, yet 1kilo-ohm would be a non existant earth.

Test between live and a stream of water from a tap, it will read close to 230v, yet it is a non existant earth. So a reading less than 230v live to earth and 0v neutral to earth usually indicates the earth being measured is not connected to actual earth at all.

Bruthal

coldelsol wrote: »

the reason my meter will not work 3 wire LNE cause the voltage between Live +E is 130V

Yes because there is no earth connection to an earth rod or neutralizing by the look of it, just an open circuit earthing setup.

I thought this may be due to bad earth spike connection which I cant find
voltage N to E 0v

Your thought is right i would say, not just a bad earth rod connection, non existant to it id bet. Once your getting 0v N-E then the earth wiring in the installstion is not connected back to an earth rod(tt) or earth rod/neutral(tn)

Earth leakage on a tt system can give less than 230v L-E but you will have greater than 0v N-E reading then. So its a non existant earth rod or not connected to it, or its hammered into a perfect insulating material:D

coldelsol

robbie7730 wrote: »

On an installation with no main earth connected to the earth bar you will get the above readings. Neutral to earth will read 0v once there is no earth leakage from any circuits. But live to earth will read less than the 230v if the earth being tested connects to nothing. If the impedence from the earth bar to earth is 1 megaohm(earth bar not connected to earth rod or neutral) as an example, and the multimeter impedence is 1 megaohm when set for voltage testing, then the reading from Live to Earth will be half of 230v or 115 volts.

This means that a reading significantly below 230v from live to earth with a digital multimeter means there is no actual main earth connection to an earth rod or neutralising connection.

It also means a poor earth connection, where for example the main earth bar is connected to an earth rod but the impedence for an example is 100 ohms, a digital multi tester will still read a full 230v.

These are reasons why proper testers like earth loop impedence testers are needed which are designed to acurately measure very low impedences.

I think we are nearly singing from same hymm book ,I am using an earth lopp imp tester its a multi do da telaris ... rccd ,insulation tester, impedence & external imp tester , and one that will not trip rccd.which has put me in good stead for a number of years and I know its not the meter cause I have cmpared readings with my own dwelling and ios consistant. the test I did was external E loop imp. so no influence from internal installation. I think from the confirmation from your self and other sparks has confirmed my suspiscions that may be the electrical suppliers earth on there steel pylon is **** and they aint bothered .just reliant on rccd,which is all fine but us brits aint convinced that they are reliable as a good sound visible connection.though I should no better I have seen what should be a tnc-s in the past in uk not so many years ago only to find that the electricity board hadn't connected there earth provision for the main earth cable which we are suppose to connect to .just shows dont take jack **** for granted.

Bruthal

coldelsol wrote: »

I think from the confirmation from your self and other sparks has confirmed my suspiscions that may be the electrical suppliers earth on there steel pylon is **** and they aint bothered .just reliant on rccd,which is all fine, but us brits aint convinced that they are reliable.

Its not really fine, as when you are getting this 130v Neutral to Earth because of a non connection to an earth from the installation, the RCD likely wont work in earth fault conditions, all that will happen is the earthing will come up to 230v potential, and no fault current will flow.

Try your RCD tripping tester on it.

coldelsol

M cebee wrote: »

for TT with ADS via rcd i think your fault loop impedance should be up around 200ohm or more

as robbie said it sounds like there's a problem if your voltage tester is showing 130 L-E

not familiar- but for TT i'd prob switch off power and check external fault loop impedance

is spain TT ? and what's the rcd's trip currents

Thank you for reply.
The rccd tester has 1/2 & 1 x 1 & x5 30mA and will not work cause it indicates earth not present unless I double up N&E to make test which th etripping times are well underneath 40mS and dosent trip at 1/2 .the confusion is there is a voltage between L & E of 130volts so to me indicates there is earth but not a good one!cause im looking for a potential difference the same as L-N of 230volts or as close as but 130volts is the attention I am trying to resolve .In the past in Uk I have worked on tt system which is rare for an mainly urbanisation spark,have installed earth spike and had better readings than some tnc-s systems but this is doing my head in, cause I feel I could be leaving my customer in an hazardous situation and dont want to be reliant on a rccd 30mA I cant even test the tripping time to be assured that it right unless i double up as mentioned. .the thing is I am picking up on someone elses work wether they are negligent or incompetent and I dont wish to be either.but if I cant improve on whats there then I have done all I can

Bruthal

coldelsol wrote: »

.the confusion is there is a voltage between L & E of 130volts so to me indicates there is earth but not a good one!cause im looking for a potential difference the same as L-N of 230volts or as close as but 130volts is the attention I am trying to resolve .

No the 130 volts live to earth tells me there is absolutely no earth, no confusion. It does seem to cause confusion with sparks this thing.

But i will try anyway. If you have an earth wire from your socket to the DB earth bar, but the bar is connected to nothing else except other circuit earths, there is no circuit to the ground or earth. But there will be some electrical path through the plastic of the board, and plaster walls etc, but this path will be megaohms resistance.

Now your digital multi tester is connected between the live and earth at a socket. There is no earth path so you would expect 0 volts reading. But in effect you have a multi megaohm meter in series with a multi megaohm impedence (open circuit earth path) so the meter will read roughly half the supply voltage. Here is a diagram maybe to help explain.


Look at the multimeter, it is in series with the open circuit earth. The impedence between the earth bar and ground is very large (but not infinite), but so is the impedence of the multimeter itself, so its 2 very high impedences in series, so you get voltage drop across both impedences in proportion to their impedences. In your case roughly half. So the meter shows 130 volts in your case.

Bruthal

Just as a matter of interest there a while ago, i tested between a socket live and other various things.

Socket live to metal sink - 240 volts

Socket live to metal joiner on kitchen worktop(connected to nothing except wooden worktop) 170 volts
Same test with analogue meter - 55 volts.(lower impedence analogue meter)


Socket live to water from tap(into water stream) 240volts

Socket live and i holding other probe - 200 volts.

So it can be seen that once the voltage is below the supply voltage, there is no earth continuity. And even when it is at supply voltage (running water from tap) it does not mean you have a good earth. This all backs up the importance of propper testing.

coldelsol

HI Robbie
Thanks for explanation my initial instinct was no earth or bad earth connection. I do have my 2381 & 2391 test & insp ,but never came accross a reading like this before and hadnt taken into account the impz on meter.

So back to the job in hand ,it may be some weeks b4 I get there but I will keep you all updated on the results .

Thanks again for your time

Col

Bruthal

Yes even put one lead onto a live terminal and the second lead not even connected to the meter, then connect the second lead to the meter but the probe to nothing, and a reading will come up.

Also if 230v is supplying a very high impedence load, 100 kilo ohms again for example, impractical but just for example, and the neutral is cut, a person holding the 2 ends of broken neutral will feel nothing, but the meter will still read close to 230v, again because of its own high impedence in series with the 100 kilo ohm load. Calculate the current through the resistance and the meter in series and then the volt drop across the 100k ohm resistance, and across the meter taking it as 1 megohm and it will show about 20v across the resistance load and 210v across the meter.

In reality the digital multimeters are a few megohms i think, so in the above setup it would show almost the full 230v. But a persons resistance in series with the 100k ohm load will leave them with about 5 volts across them and 225 across the 100 kilo ohm load.

Bruthal

coldelsol wrote: »

the over head pylon is 20mtr from house so I did an earth loop test at the supply meter mounted on pylon using the earth connection to the pylon thinking you wont get better than that and run a seperate wire connected from the pylon to MET in DB, guess what no difference at all. the ground here is major rock and thinking there may be no improvement on what the electric supplier has achieved when they connected there earth connection to ground.

Judging by the above quote, maybe they never bothered earthing the neutral back at the supply transformer or along its length at all, so its an isolated supply in effect, which would give you the readings your getting too.