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.

 

[SparkyChick]

They may have repaired the local earth spike for the transformer, or put a new rod in.

 

[SparkyChick]

But could be different ground conditions... we've had a lot of rain so the water table may be higher making the ground more conductive closer to the surface, thus improving the rods performance.

 

[AJshep]

Id agree with Sparkychick.
Answering your question, RA is the sum of the resistances of the earth electrode (to Earth) and its using the mass of earth as its conductor, so a nice new earth at a transformer would reduce your reading.

Sounds like your pretty close to the transformer so if you were getting a reading of 400ohms other people down the road probably had readings up in the 1000 I expect someone complained so DNO had to sort it out.

 

[Wilko]

Hi - that is their local rod for PME and your earth loop now goes to that by the looks .

 

[Bellendian]

Your rods might have a nice short route back to new dno rods, soil might be wetter than it was last time, or possibly nextdoor converted to pme, but old tt rod nextdoor still connected or bonded water mains close together giving a better path back. Loads of possibilities.

 

[Nigel]

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

In fact it is impossible.

 

[Ian1981]

Did you do a Ra electrode test or was it with a loop tester?

 

[westward10]

It must have been an elfi test.

 

[Bellendian]

Yep ok, agree it wouldn't affect Ra if measured with electrode tester.
But it could change a Ze done with a loop tester, which I guess is what you're getting at?

 

[UKMeterman]

They may have repaired the local earth spike for the transformer, or put a new rod in.

I know of one property where I had reported that the local earth conductor had been liberated from the local transformer pole...

 

[PEG]

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

In fact it is impossible.

I will have to say,that is incorrect,fella.
Unlikely,would be a fair statement,but certainly not impossible.

 

[Nigel]

I will have to say,that is incorrect,fella.
Unlikely,would be a fair statement,but certainly not impossible.

Please school me.

 

[PEG]

Would not dream of doing so,friend.
Just imagine the tasks one would perform,either intentionally,or deliberately,to improve the Ra on a particular installation.
Now consider,if any work or task,agents from a DNO would or could carry out,and how this could affect things.

 

[Nigel]

Would not dream of doing so,friend.
Just imagine the tasks one would perform,either intentionally,or deliberately,to improve the Ra on a particular installation.
Now consider,if any work or task,agents from a DNO would or could carry out,and how this could affect things.

I honestly swear I cannot think of anything.