Earthing Rod

[johnb2713]

I was asked a question the other day regarding TN-C-S system. Does it cause any issues if an earthing rod is connected into the system to avoid the potential problem of the Neutral becoming disconnected?

I cant think of any reason it would cause an issue other than appliances still running ok between live and earth in the absence of a neutral, I would however appreciate your thoughts on the subject.

J

 

[binky]

That's a subject much discussed previously on here. There's no easy answer as it depends where the neutral gets broken. In theory there should be multiple rods to earth along the grid supply, in reality we haven't got a clue how the grid has been installed. The main worry is if your neighborhood has lost the neutral and you haven't, your rod can become the easiest return path for the neighborhood.

 

[Murdoch]

This is a can of worms

Best you put the lid back on this subject and move on

 

[johnb2713]

Sorry guys, I didnt know this was such an emotive subject. I will shut up and crawl back under my stone LOL.

J

 

[UNG]

I have seen the reality of this, previous spark didn't want to call the DNO so in went an earth rod connected to the MET and gave a Ze of 37Ω, after a few issues go to look at the installation the supply was looped from next door so knocked next door and I asked if I could do a few tests and surprise surprise Ze was 37Ω and it was the same for a few other houses so DNO called in and they had to dig to repair the earth fault. Could have been interesting if a high current fault had occured

 

[kerching]

I think I Am talking complete here but, was it not a proposal in either 18th edn or Amd1 that every installation was fitted with an earth rod??

May have dreamt it

 

[Murdoch]

I think I Am talking complete here but, was it not a proposal in either 18th edn or Amd1 that every installation was fitted with an earth rod??

May have dreamt it

This maybe :

https://professional-electrician.com/18th-edition/earth-requirements-set-go-live-18th-edition/
??

 

[binky]

Sorry guys, I didnt know this was such an emotive subject. I will shut up and crawl back under my stone LOL.

J

emotive, no, technically confusing as hell, you bet your shirt!

A friend of mine who worked for Western Power was telling me how the neutral failed in Truro shopping centre one day. The first anyone knew anything about it was everyones gas appliances going nuts. Gas Board eventually called out WPD, in the abcence of a neutral, the leccy had decided the old cast iron gas main was a good return path. As it got hotter an hotter it was heating the gas in the pipe hence the appliance issues. Apparently it was glowing red by the time WPD had isolated the leccy and dug the road up to find the fault.

 

[binky]

one of our long lost members was a great champion of TTing everything, I ws never sure how that woud work with aneutral fault if the neighbours are all TN-C-S or PME? I'm guessing without the neutral - earth link within the consumer head, a fauty neutral could not send 'leccy up your rod' ( sounds like a carry on film ).

 

[Andy™]

I was asked a question the other day regarding TN-C-S system. Does it cause any issues if an earthing rod is connected into the system to avoid the potential problem of the Neutral becoming disconnected?

I cant think of any reason it would cause an issue other than appliances still running ok between live and earth in the absence of a neutral, I would however appreciate your thoughts on the subject.

J

well BS7671 did want to make it mandatory to install an earth electrode on TNCS systems becuase the DNO are not capable of maintaning their network adequately and want us to do their job...

 

[Murdoch]

well BS7671 did want to make it mandatory to install an earth electrode on TNCS systems becuase the DNO are not capable of maintaning their network adequately and want us to do their job...

which would have meant that the DNO's would save money and we would have to give our customers bad news about changes and extra costs

Thankfully this daft idea got dropped

 

[Andy™]

maybe dropped for now, but definately not forgotten. it'll be back

 

[Mike.J]

In rural France the electrical provider does not supply an earth and leaves it to the householder.

 

[Murdoch]

In rural France the electrical provider does not supply an earth and leaves it to the householder.

No different here loads of TT systems

 

[kerching]

This maybe :

https://professional-electrician.com/18th-edition/earth-requirements-set-go-live-18th-edition/
??

Aha! My Sanity has been restored

 

[johnb2713]

Sorry guys, one more question on this subject if I may.

If I've understood it correctly, if a householder installed an earthing rod, the danger is if the neutral was lost say 50 houses upstream all of the neutral current could potentially going down this earthing rod vapourising the earth wire to the rod / potential fire issue. Is that a fair assessment?

 

[Gian]

well BS7671 did want to make it mandatory to install an earth electrode on TNCS systems becuase the DNO are not capable of maintaning their network adequately and want us to do their job...

My generator install gave several issues with regards change over switch and pme. Our issue was how the generator was bonded and how it was wounded. The change over switch works with L/N . We have 2 ev chargers with pen fault detection built in and they both did not opperator when the generator was used. In this instance as well as the way the internal generator was configured an earth rod system was installed to allow EV chargers to work. So now we are configured as tncs and also earth rods. Both separate systems were tested and all RCDs work within the specifications .

 

[UNG]

Sorry guys, one more question on this subject if I may.

If I've understood it correctly, if a householder installed an earthing rod, the danger is if the neutral was lost say 50 houses upstream all of the neutral current could potentially going down this earthing rod vapourising the earth wire to the rod / potential fire issue. Is that a fair assessment?

You have understood correctly

 

[Joules]

The compromises surrounding TN-C-S earthing is nothing short of surprising. I found some very helpful YouTube content. The first is by CW Electrical

BrokenPen Conductor - What’s Going on Inside a TN-C-S Cable Joints. PEN – Protective Earth Neutral. What was of interest was that the DNO should by rights ground spike the PEN but no one does this in practice probably because there are restrictions on how far away from services like gas and water the spike must be. So historically they have instead bonded to the copper water pipe to protect appliance metal casings becoming live if the PEN becomes disconnected from the supply cable braiding in DNO equipment. Water pipe bonding seems to give multiple safety redundancy from adjacent housing.

Relating to this is content by John Ward Earthing systems, EV charging connection options and open PEN detection devices it’s his recommendation at the end of the video that deals with ground spikes and supplemental earths.

The ground spike in use in our house is some 10 metres away from any underground services and the impedance to the PEN in parallel to the copper water pipe is 2 ohms. Lastly John Ward discusses wider issues in TN-C-S Danger - Broken PEN Conductor (CombinedEarth & Neutral)

The issue of plastic interposing or replacing copper piping is touched upon by partPtrained.co.uk toward the end of their video Earthing and Bonding - Part 5 Chapter 54 BS7671:2018 18th Edition Wiring Regulations .

 

[Andy™]

Sorry guys, one more question on this subject if I may.

If I've understood it correctly, if a householder installed an earthing rod, the danger is if the neutral was lost say 50 houses upstream all of the neutral current could potentially going down this earthing rod vapourising the earth wire to the rod / potential fire issue. Is that a fair assessment?

yes, however the resistance of the rod will not be low enough to have enough current flowing to melt anything

the biggest risk is a broken neutral and current flowing though the bonding into a water/gas pipe and using that to get to the neighbours TNCS, that can and has caused burnt out wiring before