A question about how current travels through the real earth?

[HappyHippyDad]

When testing Ze on a TT the only connection between the line and the earth rod is the actual ground.

When you do a Ze is it actually sending a small current through the actual ground from the earth rod at the house to the earth rod at the transformer?

Also, related to the above, I have 2 separate garden light circuits. The customer complained of RCD tripping. The garden lights have junction boxes buried in the ground that lead on to the next light. These Jb's are full of water hence the tripping (IR results 0.006Mohms N-E).

With regards the above paragraph I am getting 0.15Mohms between the Neutrals of both separate garden light circuits (also the earths and line's but you would expect that as light bulbs are in and 0.006Mohms N-E). This is with all the conductors completely isolated, is this again because the separate circuits have a link via the actual ground (due to all the water in the buried JB's)?

 

[Wilko]

Hi - I think it’s yes and yes .

 

[HappyHippyDad]

Hi - I think it’s yes and yes .

Very scientific

 

[Ian1981]

It’s sorcery and witch craft, that and physics.
Due to the presence of water, salts and minerals the earth is a very good conductor.
Also it stands to reason as when you receive an electric shock you complete the circuit via the ground by the potential difference.

 

[stevethesparks]

It’s sorcery and witch craft, that and physics.
Due to the presence of water, salts and minerals the earth is a very good conductor.
Also it stands to reason as when you receive an electric shock you complete the circuit via the ground by the potential difference.

I want to know how I can still get a belt when on my supposedly insulated step ladders made from glass fibre?

 

[Ian1981]

I want to know how I can still get a belt when on my supposedly insulated step ladders made from glass fibre?

I’ve never tested to see how well insulated they are personally or by experience.
Was your body in contact with anything else?

 

[stevethesparks]

It was a rhetorical question in jest.
However, just to satisfy, I may give it a go later after a few ciders, see if I report back

 

[Ian1981]

It was a rhetorical question in jest.
However, just to satisfy, I may give it a go later after a few ciders, see if I report back

Have a few more ciders, it might not hurt as much..

 

[DPG]

I want to know how I can still get a belt when on my supposedly insulated step ladders made from glass fibre?

If made of true glass fibre then the resistance should be of such magnitude that a shock would be almost impossible. Was it a damp day? Were they good quality ladders or ebay specials?

 

[telectrix]

It was a rhetorical question in jest.
However, just to satisfy, I may give it a go later after a few ciders, see if I report back

try jumping upand down on the fibreglass steps. if you get it right... 50 times a second, and in harmony, your feet should only touch the steps when the supply sine wave is at 0v. then you'll feel nothing except aching feet.

 

[stevethesparks]

try jumping upand down on the fibreglass steps. if you get it right... 50 times a second, and in harmony, your feet should only touch the steps when the supply sine wave is at 0v. then you'll feel nothing except aching feet.

Will I need an oscilloscope?

 

[telectrix]

only to see if there's any brain activity after you tried it.

 

[happysteve]

When testing Ze on a TT the only connection between the line and the earth rod is the actual ground.

When you do a Ze is it actually sending a small current through the actual ground from the earth rod at the house to the earth rod at the transformer?

Also, related to the above, I have 2 separate garden light circuits. The customer complained of RCD tripping. The garden lights have junction boxes buried in the ground that lead on to the next light. These Jb's are full of water hence the tripping (IR results 0.006Mohms N-E).

With regards the above paragraph I am getting 0.15Mohms between the Neutrals of both separate garden light circuits (also the earths and line's but you would expect that as light bulbs are in and 0.006Mohms N-E). This is with all the conductors completely isolated, is this again because the separate circuits have a link via the actual ground (due to all the water in the buried JB's)?

As Wilko said: yes, and (probably) yes.

I had an issue with low insulation resistance on a circuit I was going to alter - the IR reading wasn't low enough to trip the RCD, but was below the minimum so I had to find the cause and rectify before doing any work.

I found it fairly quickly on an old pond pump. The slightly strange thing was that the exterior socket it was plugged in to wasn't even wired up correctly - the earth had been terminated at the (pointless) earth terminal in the plastic casing, rather than the earth terminal of the socket:

So the leakage was between one of the live conductors (don't know which, and I don't care) and the actual earth, then to the installation earth via the lead sheath of the incoming supply (TN-S, though I suspect the supply infrastructure was PME). Intrigued, I did an insulation resistance test between live and... well, I just poked by test probe in the ground.

Here's the video:

 

[Des 56]

Hi- I think its "possibly" for the first part and "yes" for the second

Although you have a TT earth system it may not be so for the whole of the supply line
If its a TT derived from a Tnc-s supply then the current may get back to the star point via Pme rods whilst on its way back home

 

[edexlab]

Re Current flowing through the actual earth

When I was at college it was explained to us like this;

"Everything is a conductor, an insulating material is a poor conductor but still a conductor,

Soil, water, minerals etc are poor conductors

The earth is basically millions of poor conductors in parallel resulting in the earth being a conductor which can have a low enough resistance to be used as a return path"