Step and Touch Voltages

[Alasdair82]

Wondred if anyone had experience of step and touch voltage measurement and what values are normally measured in the field. Did a test today and got a value of 12.1V for Touch and 31.4V for step potential. Wondered if this was inline with the "Norm".

 

[Marvo]

How did you make the measurements? What instrument or tester did you use?

 

[Alasdair82]

How did you make the measurements? What instrument or tester did you use?

Hi Marvo
Meggar DET 2/2. PFC supplied by DNO on site was 1.210 KA

 

[Alasdair82]

Measurements were made with stake 100m away, touch potential was with a metal plate on the ground 1m away from the stair on the structure. Step potential was measured with the stake 100m away and two metal plates 1m away from the structure foundation and 1m each apart.

 

[onions1066]

For what reason were you taking these measurements?

 

[Marvo]

What voltage is present in or around the structure where your measurements were taken? What regs are you working to, is this some type of special location? Also as per Onions question, why is there a possible need to take step and touch voltages.

 

[Alasdair82]

What voltage is present in or around the structure where your measurements were taken? What regs are you working to, is this some type of special location? Also as per Onions question, why is there a possible need to take step and touch voltages.

Power Generation side . IEEE Std 80-2000 applies to substations and power generation sites as well as pylons etc.

 

[onions1066]

This isn't a penis measuring competition. I can see your smart so why are you taking the readings?

 

[Alasdair82]

Client request. Requirement needed before the Germans come over to complete commissioning. Touch voltage is as I expected and meets the criteria for a disconnection time of over 1 second. The reason I am asking is that the step potential was to me surprisingly low as well as I expected it to be a bit higher, as per calculation this can be up to a few hundred volts or thousand volts when designing earth grids. It is more about how real measured results compare with the calculated ones by design. Just wondering if others had experience of step and touch measurements and what magnitude of results they had in the past.

 

[GLENNSPARK]

here..:

http://www.weschler.com/_upload/sitepdfs/techref/gettingdowntoearth.pdf

 

[Engineer54]

Power Generation side . IEEE Std 80-2000 applies to substations and power generation sites as well as pylons etc.

Errr, that's an Americian Standard mate, not a BS/ES one, although they could be equivalent, i haven't bothered to check!!

 

[Marvo]

This isn't a penis measuring competition. I can see your smart so why are you taking the readings?

Yeah, wrong tester for the job, you be pushed to get an accurate penis measurement with a Meggar DET 2/2.

The differences between calculated and measured values are due to inconsistancies in soil resistivity and the fact the earth grid is not a single point, it's a highly irregular shape that is difficult to represent accurately in calcs. Also large differences will be seen seasonally with varying moisture content of the soil and freezing of ground. I would expect any measured step voltage at this time of year in the UK to be significantly lower than the calculated values.

 

[Engineer54]

Client request. Requirement needed before the Germans come over to complete commissioning. QUOTE]

What are the Germans coming over to commission??

 

[Marvo]

It's difficult to make focused comments on this because info isn't very forthcoming on the installation, I suspect this is why every question Alistair asks is met by mostly new questions. If it's not top secret maybe you can give us a complete run down of exactly what the installation and testing is about.

 

[Alasdair82]

It's difficult to make focused comments on this because info isn't very forthcoming on the installation, I suspect this is why every question Alistair asks is met by mostly new questions. If it's not top secret maybe you can give us a complete run down of exactly what the installation and testing is about.

It is a power generation site with a Wind Turbine. Basically that is irrelevant to my question and does not affect step and touch results. The question relates to earthing grids and not what is on them. The Meggar Test procedure was followed and can be found here on pages 24 & 25

http://www.biddlemegger.com/biddle-ug/DET2_2_UG.pdf

Not sure how much more information I can give and I appreciate the input

 

[Alasdair82]

Yeah, wrong tester for the job, you be pushed to get an accurate penis measurement with a Meggar DET 2/2.

The differences between calculated and measured values are due to inconsistencies in soil resistivity and the fact the earth grid is not a single point, it's a highly irregular shape that is difficult to represent accurately in calcs. Also large differences will be seen seasonally with varying moisture content of the soil and freezing of ground. I would expect any measured step voltage at this time of year in the UK to be significantly lower than the calculated values.

Thanks for that Marvo, I did suspect that the wet ground would signifigantly lower the readings. Think these forums get off topic at times. What I asked was what others had experienced in measurments.

The DET 2/2 was specified by the client in their engineers design procedures. It does take a measurement between the points but is a resistance rather than a voltmeter. We had suggested to use the Metrel MI3295 as an instrument but they were not willing to pay the money, hence the reason for using the DET 2/2 as they requested.

We did follow the procedure outlined by meggar and my question was really to all the other users who have commented on this post on their experience of what readings might be through their own experience of taking step and touch readings.

For Engineer 54 ,
IEEE Stds 80 was specified by the Client, who are based in Germany. If there is a BS number for grounding of AC substations I would be delighted to know what it was.

So far the client seemed happy enough with the results.

Again I was wondering what people who had done this testing on a regular basis experienced in the field in terms of voltage levels.

 

[Engineer54]

For Engineer 54 ,
IEEE Stds 80 was specified by the Client, who are based in Germany. If there is a BS number for grounding of AC substations I would be delighted to know what it was.

You'll have to check yourself,(memories not as sharp as it was) but as i remember BS 7354 is the standard you're after

 

[Alasdair82]

You'll have to check yourself,(memories not as sharp as it was) but as i remember BS 7354 is the standard you're after

Thanks Engineer54