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.

 

[Midwest]

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

Come on @DPG, I bet you like all those leotards and tap shoes.

 

[DPG]

Maybe. Not saying.

 

[Dave OCD]

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

Me too PEG , and today I was on such a fault finding mission. It involved measuring below and then lifting a 9"square of upstairs chipboard flooring- which still had the original old floorboards beneath. Fault 1 was a badly terminated live in a broken pendant base used as a JB in the void above the lounge light and fault 2 was a burned 1mm squashed behind a heating pipe, very satisfying to find,fix then test and get good results, I'm the 3rd Electrician called in to sort out this one [and the 1st invited via recommendation], knackered now though.

 

[Nigel]

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?

Eh?

 

[johnduffell]

measuring below and then lifting a 9"square of upstairs chipboard flooring

That's impressive, how did you work out the location of the fault, was it something fancy like time domain reflection to find out the distance to the fault, or something less exotic like a mirror and steel tape?

 

[Dave OCD]

It was a combination of experience, optimism and desperation. And measuring carefully to lift the floor exactly above the living room light fitting.

 

[weevilward]

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?

So if there are dodgy DNO rods out there leading to a very high ELFI - Isn’t a Ze test more meaningful (and important) than a dead Ra test? After all, the touch voltage and the successful operation of the RCD depends on the EFLI being low enough. You could have the best customer earth rod in the world but if the nearby DNO rod is pants then the EFLI will be very high.

 

[PEG]

It was a combination of experience, optimism and desperation. And measuring carefully to lift the floor exactly above the living room light fitting.

Nice one....Delboy and Rodney needed a man like you,for that chandelier....

 

[HappyHippyDad]

Opening myself up here, but I have very little knowledge of the electrics outside of the domestic situation.

Am I right in thinking that at the transformer there is an earth rod (similar to a domestic one, just bigger?) in the ground and this is attached to the neutral at the transformer?

 

[Deleted member 26818]

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?

I don’t see that happening, as the RA is just the resistance of the electrode and the earth conductor combined to earth.
Whereas what PEG is describing is the Ze.

 

[Deleted member 26818]

Opening myself up here, but I have very little knowledge of the electrics outside of the domestic situation.

Am I right in thinking that at the transformer there is an earth rod (similar to a domestic one, just bigger?) in the ground and this is attached to the neutral at the transformer?

In most instances yes.

 

[Mike Johnson]

For anyone interested this is the requirements for earthing in France: Mise à la terre d'une installation électrique, norme NF C 15-100 - https://www.schema-electrique.net/mise-a-la-terre-installation-electrique-norme-NF-C-15-100.html Google translate is your friend, or set Google to translate automatically.