Why did the Ra go from 180Ω to 14Ω?

[HappyHippyDad]

About a year ago I went to a property to do some work. It is a TT and the Ra was something like 300Ω or 400Ω, I cant remember exactly. I put in 2 new rods 5/8" and it came down to around 180Ω, still poor but <200Ω.

I went back today for some more work and the customer said an electrician had been out next door and got Western Power (WP) out with regards 'something to do with the earthing'.

Before I started my work I checked the Ra as I wanted to make sure it was stable at <200Ω. It measured as 14Ω.

My customer took me to the electricity pole (I guess this is the transformer) on her property (large field) and showed me where she thinks the work was carried out. On either side of the pole is a cable which runs into the ground, one of these is where she thinks the work was carried out. What would WP have done to improve the Ra? I thought the Ra was related just to the customers earthing system, i.e rod etc.

 

[PEG]

Hi bud,the first i encountered,was at a Victorian semi,with cellars,where the TT earth connection,disappeared in to the cellar wall,as is common in this type of property,to,i suspect,the lead water or steel gas service pipe.
The DNO attended the property next door,where an elderly couple,had an electrician attend,and flagged an earthing issue,which the DNO accepted,was their responsibility to maintain,as they had completed repairs there, sometime in the seventies.

Whatever they did,during their 4 hour visit,plummeted the Ra at the property we were sorting,from the 30's,to just over 1.

I suspect their improvement,was back-feeding a benefit,through a shared or defunct service pipe,via the bonding.This improved Ra,remained the same,without variation,on subsequent visits.

The second occasion,was a rural property,where the TT rods,of which there were three,were in a line along the boundary. The ground was back-filled,and raised,and i would guess that this was the reason for the three rods.

The DNO moved a pair of transformer poles,to a new position,right next to the rods,due to some expansion,of the farm next door.
There was some carry-on,as the pole auger vehicle,got stuck,and the efforts to make a hard-standing for it to work,resulted in some top soil,being banked over the boundary,and two rods.

The links,between the rods,were underground,anyway,but the steady,summer Ra of about 150,was 20-30 when tested,2 days after they cleared site,and although i have only ever tested during summer,it appears stable.

It is not that long ago,that the work done,by any DNO,was a tad "individual",to say the least,where certain methods of work were driven more by sole characters ideas of methodology,and not rules and directives.
I have been told dozens of stories,by some of the older lads from National Grid,when i worked their sites at Carrington and Penwortham,of how they enabled expected earthing values,for a surprise visit from an engineer,Friday afternoon.....

Believe nothing you hear...only half of what you see...and never,say never

 

[Nigel]

Hi bud,the first i encountered,was at a Victorian semi,with cellars,where the TT earth connection,disappeared in to the cellar wall,as is common in this type of property,to,i suspect,the lead water or steel gas service pipe.
The DNO attended the property next door,where an elderly couple,had an electrician attend,and flagged an earthing issue,which the DNO accepted,was their responsibility to maintain,as they had completed repairs there, sometime in the seventies.

Whatever they did,during their 4 hour visit,plummeted the Ra at the property we were sorting,from the 30's,to just over 1.

I suspect their improvement,was back-feeding a benefit,through a shared or defunct service pipe,via the bonding.This improved Ra,remained the same,without variation,on subsequent visits.

The second occasion,was a rural property,where the TT rods,of which there were three,were in a line along the boundary. The ground was back-filled,and raised,and i would guess that this was the reason for the three rods.

The DNO moved a pair of transformer poles,to a new position,right next to the rods,due to some expansion,of the farm next door.
There was some carry-on,as the pole auger vehicle,got stuck,and the efforts to make a hard-standing for it to work,resulted in some top soil,being banked over the boundary,and two rods.

The links,between the rods,were underground,anyway,but the steady,summer Ra of about 150,was 20-30 when tested,2 days after they cleared site,and although i have only ever tested during summer,it appears stable.

It is not that long ago,that the work done,by any DNO,was a tad "individual",to say the least,where certain methods of work were driven more by sole characters ideas of methodology,and not rules and directives.
I have been told dozens of stories,by some of the older lads from National Grid,when i worked their sites at Carrington and Penwortham,of how they enabled expected earthing values,for a surprise visit from an engineer,Friday afternoon.....

Believe nothing you hear...only half of what you see...and never,say never

This sounds like Ze not Ra??

 

[davesparks]

There is no reason why anything the DNO does will affect your Ra.

In fact it is impossible.

I don't think it's impossible, just very unlikely.
It sounds like the DNO's earth rods are reasonably close to the installations earth rod.
My knowledge is a bit rusty here but I think if the DNO have increased the length of their earth rods the spheres of influence may now overlap where they did not before and thus affect Ra.
I think the effect on the measured Ra will depend on which test method is used, I doubt it would affect a 3 wire fall of potential test but a clamp tester or direct measurement may be affected.

Obviously if it is not Ra which is being measured but Ze by and efli test then whatever the DNO have done could have a big effect.

 

[Marvo]

....It is a TT and the Ra was something like 300Ω or 400Ω, I cant remember exactly. I put in 2 new rods 5/8" and it came down to around 180Ω, still poor but <200Ω......

Assuming you mean Ra and not Ze, you put new rods in and over time the disturbed ground around the rods will naturally settle and compact against the rod. This is especially so if you had long rods with couplings along their length.

I've installed deep earth rods and earth nests that have tested 6.5 ohms when installed and two years later were down to 2 ohms when retested.

 

[HappyHippyDad]

I think I should give some apologies here. I thought that the correct term for the measurement you get when doing the external earth fault loop impedance for a TT was Ra rather than Ze.

I have used a MFT to do a external EFLI test, so I should have said Ze.

 

[PEG]

This sounds like Ze not Ra??

Nope,we are talking Ra,in it's meaning of "...total resistance of the earth electrode and the protective conductor connecting it to exposed parts..."
The methods used to test this,were not a bone of contention,in the OP's post.

My assertion that work carried out by any DNO,can vary the test readings,whatever method of test is used,stands.

I'm prepared to accept potAto/potARto,tomAto/tomARto...lets call the whole thing off...it was only the word "impossible",that got me going....

 

[Bellendian]

Ah....I have to admit that I don't possess an electrode tester, and only use the efli test method on tt.
I had it in my head that if you did a bone-fide Ra test, then you were literally just testing the electrode to the test probes in isolation, i.e. the earthing conductor would not be connected to the electrode under test.
If the earthing conductor remains connected, then the effects of any DNO activity could still be seen?

 

[PEG]

It is the method of choice,usually,due to many reasons. Not having easy access to disconnect the earthing conductor...not being able to stick your spikes in at the correct spacings...time...patience...etc

As for any work the DNO could do,having an effect on the readings on an earthing electrode,tested in isolation...again,unlikely but certainly possible - as are a myriad of other entities,being the cause of varying any other result we seek in life.

I have prided myself,on the ability to discover faults,where others had either failed,or give up. One of the most useful assets,in these endeavours,is never discount any variable - however bizarre or unlikely

 

[Nigel]

Ah....I have to admit that I don't possess an electrode tester, and only use the efli test method on tt.
I had it in my head that if you did a bone-fide Ra test, then you were literally just testing the electrode to the test probes in isolation, i.e. the earthing conductor would not be connected to the electrode under test.
If the earthing conductor remains connected, then the effects of any DNO activity could still be seen?

Ra is a dead test. If you are carrying out the EFLI test, which is a live test, this is called Ze.

 

[telectrix]

OMG. I've agrred with essex. that's twice in under 10 years. this has to stop. knuckes rapped. .

 

[Harry_P]

It is the method of choice,usually,due to many reasons. Not having easy access to disconnect the earthing conductor...not being able to stick your spikes in at the correct spacings...time...patience...etc

As for any work the DNO could do,having an effect on the readings on an earthing electrode,tested in isolation...again,unlikely but certainly possible - as are a myriad of other entities,being the cause of varying any other result we seek in life.

I have prided myself,on the ability to discover faults,where others had either failed,or give up. One of the most useful assets,in these endeavours,is never discount any variable - however bizarre or unlikely

the other useful asset needed is a client willing to pay for your protracted fault finding endeavours (unless you do it for free)

 

[PEG]

the other useful asset needed is a client willing to pay for your protracted fault finding endeavours (unless you do it for free)

Alas,yes,this would be the driving factor,i suppose,with many jobbing sparkies...

I do not fit in to that category,so my reasons for getting involved and stuck-in,to a quandary,are different.

Customers who tell you half a story,give you rules,times,costs and a flatulent pet,to work round....are NOT my idea of fun

Those that have to face such obstacles,have my respect and sympathy

 

[richy3333]

It's Friday, I have popcorn and wine and am now awaiting Essex"s explanation as PEG rose to the challenge and gave his.

So Essex can we hear your theory for the argument on the flip side please?

 

[Midwest]

It's Friday, I have popcorn and wine and am now awaiting Essex"s explanation as PEG rose to the challenge and gave his.

So Essex can we hear your theory for the argument on the flip side please?

Some people watch Strictly or X Factor for their weekend excitement.

 

[richy3333]

Strictly's finished and my work pants can't take any more sequins!