Hi guys. To those in countries with TNC-S. What are your requirements regarding installation of earth rods for domestic installs?

[LastManOnline]

Because broken PEN faults on the DNO system can and do happen, and when they do they can be incredibly dangerous.

The advantage I see, as long as earth electrodes are properly installed in accordance with a well written regulation, is that the danger under a broken PEN fault will be greatly reduced.
Initially when the regulation comes in to effect there will be little difference but, after a few years, and as more and more installations have earth electrodes installed the overall effect will be to create a network where the dangers under PEN fault conditions are reduced.

If the regulations were to require an earth electrode system of <20ohm Ra connected to the first consumers earth terminal after the point of connection to the DNO's PME supply (this kind of wording should avoid anyone trying to connect earth rods to a 10th storey flat) then once multiple installations have them connected the combined effect could easily be <2 ohms.
So for the majority of PEN faults which affect more than one installation we end up with a very low resistance path to earth connected and minimised danger.

Of course then we will need a means of alerting people to the fact that the supply neutral has failed.
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I've never used a galvanised rod, only the copper bonded steel rods available in 4' and 8' lengths with threaded ends for screwed couplings.

I fully agree. Having a low, resistance earth electrode network is the key to dealing with the dangers of broken neutrals in a TNCS system. A low resistance return path will prevent bonded metalwork from becoming live. Those kinds of low resistance values would require not one but several rods or a mesh. It's, interesting to look back at ElectroChems comment about how people have been electrocuted in Australia under broken neutral situations DESPITE the earth rod been Installed and this is because the resistance is way to high. We have had similar issues here. So it really is, nt a question of should we or should, nt install an electrode. The question in my view is why are we not installing an earth electrode with a resistance low enough to deal with the issues raised by broken neutrals

 

[davesparks]

The question in my view is why are we not installing an earth electrode with a resistance low enough to deal with the issues raised by broken neutrals

Because the regulations don't require it and the majority of installers will always work to the minimum standard rather than the best they can achieve.

This is one thing the USA do better than us, they install an electrode system made up of 2x 8' earth rods as standard (they only need one if it is less than 25ohms to earth but they don't usually test anything and just install 2 regardless)

 

[LastManOnline]

Because broken PEN faults on the DNO system can and do happen, and when they do they can be incredibly dangerous.

The advantage I see, as long as earth electrodes are properly installed in accordance with a well written regulation, is that the danger under a broken PEN fault will be greatly reduced.
Initially when the regulation comes in to effect there will be little difference but, after a few years, and as more and more installations have earth electrodes installed the overall effect will be to create a network where the dangers under PEN fault conditions are reduced.

If the regulations were to require an earth electrode system of <20ohm Ra connected to the first consumers earth terminal after the point of connection to the DNO's PME supply (this kind of wording should avoid anyone trying to connect earth rods to a 10th storey flat) then once multiple installations have them connected the combined effect could easily be <2 ohms.
So for the majority of PEN faults which affect more than one installation we end up with a very low resistance path to earth connected and minimised danger.

Of course then we will need a means of alerting people to the fact that the supply neutral has failed.
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I've never used a galvanised rod, only the copper bonded steel rods available in 4' and 8' lengths with threaded ends for screwed couplings.

Hi Dave,
Just saw that I did, nt reply to you on this one. I think your summary is 90% good, but requires one adjustment. Your thought that multiple installations installing individual earth rods will lower the overall resistance and make a more effective return path under broken PEN circumstances.True if the broken Pen is some distance from your home, but if it happens outside your home then ADS is entirely dependent on the resistance of YOUR electrode.

Anyway, I have appreciated all the comments, and it's been interesting to note how the role of the earth electrode still seems to be a matter of debate and to some degree even controversy

I thought I,d leave the final word on the matter to John Ward, whose views I, ve come to respect,

Regarding the common belief that the earth rod is a backup for a broken PEN he states.."If you thought your rcd, s will operate when the DSO, s neutral breaks, you would be WRONG.." (Utube video)

Regarding the earth electrode in a TNC-S system... " to have any real effect the electrode would need a VERY low resistance, well under 10 ohms. In practice that will be next to impossible with a single rod.. "

 

[davesparks]

True if the broken Pen is some distance from your home, but if it happens outside your home then ADS is entirely dependent on the resistance of YOUR electrode.


Regarding the earth electrode in a TNC-S system... " to have any real effect the electrode would need a VERY low resistance, well under 10 ohms. In practice that will be next to impossible with a single rod.. "

Yes but the chances of a broken PEN occurring at all are very small, the chances of it occurring in such a location that it affects only a single installation are a vanishingly small fraction of the chances of it happening in the first place.
You cannot guard against absolutely every fault, but you can guard against the vast majority, and the fact that a fault could occur affecting just one installation is not a valid reason to not protect against faults which could affect multiple installations.


The simple answer to your last comment is to install more than one rod if a single rod is not sufficient, just look at the USA where they generally install 2x 8' rods minimum for a house service, and I think they space them at least 16' if I remember correctly (their code allows a single rod if it has a suitably low Ra, but they never do any testing so they just install 2 rods).

 

[LastManOnline]

Yes but the chances of a broken PEN occurring at all are very small, the chances of it occurring in such a location that it affects only a single installation are a vanishingly small fraction of the chances of it happening in the first place.
You cannot guard against absolutely every fault, but you can guard against the vast majority, and the fact that a fault could occur affecting just one installation is not a valid reason to not protect against faults which could affect multiple installations.


The simple answer to your last comment is to install more than one rod if a single rod is not sufficient, just look at the USA where they generally install 2x 8' rods minimum for a house service, and I think they space them at least 16' if I remember correctly (their code allows a single rod if it has a suitably low Ra, but they never do any testing so they just install 2 rods).

Yes the chances are small but as you said in one of your previous posts "They can and do happen.. and are incredibly dangerous".

You may have misunderstood what I am proposing. I am critical of the current earth electrode arrangement not because I don't think they should, nt be ther. I think they are in fact vital. It's just that the current arrangement of a 4 foot rod is not fit for purpose.

The American system is certainly better, (two 8ft rods) but how much better?. They don't test so they have no idea if the arrangement functions.

 

[7029 dave]

My option with a TNCS, is that an earth mat or nest should be linked to every such earthing arrangement.

 

[davesparks]

My option with a TNCS, is that an earth mat or nest should be linked to every such earthing arrangement.

Whilst it would be a very good earth, it would be very hard to implement in any existing building, and incredibly expensive for small installations such as houses.
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You may have misunderstood what I am proposing. I am critical of the current earth electrode arrangement not because I don't think they should, nt be ther. I think they are in fact vital. It's just that the current arrangement of a 4 foot rod is not fit for purpose.

The American system is certainly better, (two 8ft rods) but how much better?. They don't test so they have no idea if the arrangement functions.

I agree that a single 4' rod is not fit for purpose. Even a single 8' rod would be a big improvement when you consider the first 2' to 3' can be affected by seasonal variations quite significantly.

The problem we would have is that if you make the requirements too unwieldy more and more people will ignore them for the smaller installations, the requirements need to be realistically practical as well as improving safety.

I believe that for all new builds and extensions a requirement to connect an earth to the reinfircing in the foundations would help the situation greatly, however I think this would require something put into the building regulations to ensure that it happens. Electrician's often don't get involved until after the foundations have been poured, and builders/groundworkers won't be in any rush to help out even if the electrician has spoken to them in time, it would need to be in the building regs and be part of the LABC inspection of the foundations.

 

[7029 dave]

Whilst it would be a very good earth, it would be very hard to implement in any existing building, and incredibly expensive for small installations such as houses.

Yes I agree the cost would be expensive, but we should start somewhere, maybe with new builds for starters.
The dangers of a broken PEN can be catastrophic.

 

[LastManOnline]

My option with a TNCS, is that an earth mat or nest should be linked to every such earthing arrangement.

Agreed. That would be the ideal solution
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Yes I agree the cost would be expensive, but we should start somewhere, maybe with new builds for starters.
The dangers of a broken PEN can be catastrophic.

Agreed. This is not
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Agreed. That would be the ideal solution
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Agreed. This is not an issue that can be ignored indefinately

 

[LastManOnline]

Whilst it would be a very good earth, it would be very hard to implement in any existing building, and incredibly expensive for small installations such as houses.
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I agree that a single 4' rod is not fit for purpose. Even a single 8' rod would be a big improvement when you consider the first 2' to 3' can be affected by seasonal variations quite significantly.

The problem we would have is that if you make the requirements too unwieldy more and more people will ignore them for the smaller installations, the requirements need to be realistically practical as well as improving safety.

I believe that for all new builds and extensions a requirement to connect an earth to the reinfircing in the foundations would help the situation greatly, however I think this would require something put into the building regulations to ensure that it happens. Electrician's often don't get involved until after the foundations have been poured, and builders/groundworkers won't be in any rush to help out even if the electrician has spoken to them in time, it would need to be in the building regs and be part of the LABC inspection of the foundations.

Agreed. The solutions have to be realistic. This issue was, nt caused overnight and certainly wo t be solve overnight. I think first step needs, to be an industry wide recoqnition of the issue and then a realistic balanced approach to solving it. For instance, as previously mentioned, underground TNCS supplies are much less at risk. I would suggest beginning with looking at measures first in areas with overhead supplies which tend to pose the greatest risks.

 

[LastManOnline]

Agreed. The solutions have to be realistic. This issue was, nt caused overnight and certainly wo t be solve overnight. I think first step needs, to be an industry wide recoqnition of the issue and then a realistic balanced approach to solving it. For instance, as previously mentioned, underground TNCS supplies are much less at risk. I would suggest beginning with looking at measures first in areas with overhead supplies which tend to pose the greatest risks.

Agreed. The solutions have to be realistic. This issue was, nt caused overnight and certainly wo t be solve overnight. I think first step needs, to be an industry wide recoqnition of the issue and then a realistic balanced approach to solving it. For instance, as previously mentioned, underground TNCS supplies are much less at risk. I would suggest beginning with looking at measures first in areas with overhead supplies which tend to pose the greatest risks.

When an electrical fault takes place inside the home protective measures are in place to ensure its cleared within seconds via mcbs and rcds. Bonding ensures that the homeowner is protected for the duration of the fault.


Is, nt it ironic that when a fault takes place outside the home (DSO, s neutral breaks) there currently are no measures in place to clear the fault. All outside metalwork (garden lights, heatpumps, electric gates etc) is now live. Co summers mcb, s and rcd, s are rendered ineffective.

Obviously we have no control over DSO, s network. But at the consumers end, what if we were to install a mains contactor? DSO, s neutral breaks, Contactor automatically decouples the live as well. Danger to home removed. DSO, s repairs fault and contactor automatically kicks in again. I don't propose this as a permanent sution, rather a stopgap. What do you think?

 

[LastManOnline]

Yes I agree the cost would be expensive, but we should start somewhere, maybe with new builds for starters.
The dangers of a broken PEN can be catastrophic.

Hi Dave. Am agreed about the "catastrophic" consequences and the "need to start somewhere". What do you think about the proposed "stopgap" solution I replied to "dave sparks" with?

 

[davesparks]

Hi Dave. Am agreed about the "catastrophic" consequences and the "need to start somewhere". What do you think about the proposed "stopgap" solution I replied to "dave sparks" with?

What is your stopgap soloution?

Bearing in mind anything intended as a stopgap will almost certainly become permanent

 

[LastManOnline]

What is your stopgap soloution?

Bearing in mind anything intended as a stopgap will almost certainly become permanent

Think I might have made a "dogs dinner" of a previous post. Did you get to read my post from Sat morning about the mains contactor which would drop out when DSO, s neutral breaks? That was a, proposed stopgap solution.
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What is your stopgap soloution?

Bearing in mind anything intended as a stopgap will almost certainly become permanent

Think I might have made a "dogs dinner" of a previous post. Did you get to read my post from Sat morning about the mains contactor which would drop out when DSO, s neutral breaks? That was a, proposed stopgap solution.

Just realised that the post I intended for you on Sat morning I inadvertently sent to myself?. Anyway just scroll back and it's there

 

[davesparks]

Think I might have made a "dogs dinner" of a previous post. Did you get to read my post from Sat morning about the mains contactor which would drop out when DSO, s neutral breaks? That was a, proposed stopgap solution

How do you see that being rolled out?

Contactors can, and do fail, this would likely cause more problems than it solves.
If the contactor is energised 24/7 until a PEN fault occurs then it will likely burn out the coil, or be stuck closed, long before a fault occurs, plus it will be a lot of wasted energy holding all those contactors closed.
If the contactor energised on the failure of the PEN with the load connected through N/C contacts there is still the risk of sticking due to years of not moving, plus the issue of getting a reliable circuit to operate it without an incoming neutral.

You can't have a soloution which fails more commonly than the fault it is supposed to protect against occurs.

Maybe thinking along those lines something could be done on the DNO's installation to signal the substation to trip out an affected distributing main when a PEN fault occurs. But again the risk of failure may be greater than the risk of the fault being protected against.

 

[LastManOnline]

How do you see that being rolled out?

Contactors can, and do fail, this would likely cause more problems than it solves.
If the contactor is energised 24/7 until a PEN fault occurs then it will likely burn out the coil, or be stuck closed, long before a fault occurs, plus it will be a lot of wasted energy holding all those contactors closed.
If the contactor energised on the failure of the PEN with the load connected through N/C contacts there is still the risk of sticking due to years of not moving, plus the issue of getting a reliable circuit to operate it without an incoming neutral.

You can't have a soloution which fails more commonly than the fault it is supposed to protect against occurs.

Maybe thinking along those lines something could be done on the DNO's installation to signal the substation to trip out an affected distributing main when a PEN fault occurs. But again the risk of failure may be greater than the risk of the fault being protected against.

We are here in Ireland heading towards a 100 % TNC-S supply system. So for us it's a question of when, not if there will be an increase in PEN faults.
It would not be realistic at this point to expect the DSO to do a u-turn and change supply system so the only real option is some protective measure.whether its your suggestion of the DSO taking some measure to trip out a, faulty line or my suggestion to trip out a contactor in the home or some other variant (or some hybrid), is all up for debate and discussion. But I think the key thing is to get a discussion going and that has happened and hopefully that will bear some fruit. Its clear that on this forum that sparks on the ground are aware and concerned and I see that as really encouraging