I find it difficult to believe that they who make the rules could be either so inept or ignorant (true sense) of what is there at the moment.
BS7671:2018 DPC - Local Earth Electrode with TN systems
- Thread starter JohnW2
- Start date
Sponsored Links
I have reported it.
Indeed so - that was, of course, the very lack of understanding of the concept/purpose of main bonding on the part of those who write the regulations to which I referred to in my most recent couple of posts.
I certainly think that 544.1.2 deserves/requires a 'comment' - as it always did.
Kind Regards, John
Has David Cockburn been co-opted onto the committee?
Sponsored Links
- Joined
- 11 Jan 2004
- Messages
- 42,733
- Reaction score
- 2,633
- Country
Lor' help us!
It's interesting that they are now saying local earth rods are required. I recall a friend in a rural village some years ago had a visit from the "electricity company" who came round to explicitly disconnect the earth rod as they were now supplying the earth. So in the past they've gone to the trouble to disconnect them, and now someone else is saying they have to be installed.
I wonder when the laws of physics changed
I wonder when the laws of physics changed
Indeed. Mind you, it's not just the "electricity company", nor only 'some years ago'. Relatively recently I have heard/seen some electricians suggesting that it was 'not allowed' and/or 'dangerous' to connect an earth rod to a TN-C-S system (do they also want to somehow 'ban' extraneous-c-ps?!), even though some countries' regulations have insisted on it for quite a long time - with us apparently soon to follow!It's interesting that they are now saying local earth rods are required. I recall a friend in a rural village some years ago had a visit from the "electricity company" who came round to explicitly disconnect the earth rod as they were now supplying the earth. So in the past they've gone to the trouble to disconnect them, and now someone else is saying they have to be installed. I wonder when the laws of physics changed
Kind Regards, John
- Joined
- 26 Aug 2016
- Messages
- 6,833
- Reaction score
- 1,010
- Country
I think it's the decline in need for bonding, if you have no gas then new houses may have no need for bonding. But the house may not be a perfect equipotential zone the main earth (or neutral) may be lost, you still want to be able to trip an RCD . not sure why they are so worried about it though.
I wonder when the laws of physics changed
I've had a flick through and it doesn't look like anyone from a DNO has replied here so I'll have a go...
Upkeep and maintenance of TNS/SNE/4 core networks has very little to do with neutral faults, inserting bits of 3 core for repairs/diversions/whatever has minimal effect on the integrity of the network as there's usually enough PILC in the ground for it to not matter. It's newer (70s onwards) underground networks that suffer. Most neutral faults are caused by Consac cable which has a plastic covered aluminium sheath which is used as a neutral earth, it wasn't really designed to be jointed on apparently, and was intended to run directly from say feeder pillar to feeder pillar. As soon as the outer sheath is compromised, by sheath damage or at a joint, water gets in and turns the aluminium to dust and the neutral and earth disappear... The next contender is Alpex cable, very similar to modern waveform cable but instead of copper concentric neutral/earth wires, they were aluminium, so the same happens as with Consac, but it's much less of a problem. After that I would say it would be broken/stolen neutral wires in an overhead system, or damage to the neutral connection on an overhead transformer. Obviously there are other circumstances where they can happen, but these are the main ones.
As for whether it's actually safe to have a rod connected in each property, I'm not sure how I feel about that, having seen singed bonding cables, gas pipes, and internal wiring following neutral faults where it has tried to find any conductive path back to the transformer, it would only be acceptable if every property had one I reckon. Modern jointing techniques require a small earth electrode (its literally a little tail of solid copper) to come out of each service joint, but it's not practicable to go banging rods down in the footpath as there would be damages to other utilities and/or inadvertent cable spikings all the time!
If you believe it should be down to the DNO to provide rods at the cutout position rather than down to the electrician, it would just be added on to the price of a new connection plus their markup. And I've never heard of anyone complaining how cheap new connections are nowadays. The same goes for the argument of installing 4 core/SNE/TNS cable, it would just get added on to the new connection costs and passed on to whoever's paying for it, and if it's a developer, they'd stick it on the price of the houses they're selling, so you just end up paying for it yourself. And equally, I've not heard many people complaining at how cheap new houses are. The DNOs offer to carry out all excavation if required, but most people choose to do their own as it's cheaper. Some offer to provide meter boxes for a cost, but again most people provide their own as it's cheaper. I can't see why it wouldn't be any different for earth rods.
In WPD at least, multi occupancy buildings are supplied with SNE/TNS earthing via a 4 core cable (but with a plastic sheath so not in contact with ground like the old PILC cables). This is usually jointed on to a 3 core main though! I would imagine having a TNS system would remove the need for supplementary earth rods, admittedly I haven't read the document in any depth, but this would make dealing with flats etc much easier.
Hope this helps in some way...
Upkeep and maintenance of TNS/SNE/4 core networks has very little to do with neutral faults, inserting bits of 3 core for repairs/diversions/whatever has minimal effect on the integrity of the network as there's usually enough PILC in the ground for it to not matter. It's newer (70s onwards) underground networks that suffer. Most neutral faults are caused by Consac cable which has a plastic covered aluminium sheath which is used as a neutral earth, it wasn't really designed to be jointed on apparently, and was intended to run directly from say feeder pillar to feeder pillar. As soon as the outer sheath is compromised, by sheath damage or at a joint, water gets in and turns the aluminium to dust and the neutral and earth disappear... The next contender is Alpex cable, very similar to modern waveform cable but instead of copper concentric neutral/earth wires, they were aluminium, so the same happens as with Consac, but it's much less of a problem. After that I would say it would be broken/stolen neutral wires in an overhead system, or damage to the neutral connection on an overhead transformer. Obviously there are other circumstances where they can happen, but these are the main ones.
As for whether it's actually safe to have a rod connected in each property, I'm not sure how I feel about that, having seen singed bonding cables, gas pipes, and internal wiring following neutral faults where it has tried to find any conductive path back to the transformer, it would only be acceptable if every property had one I reckon. Modern jointing techniques require a small earth electrode (its literally a little tail of solid copper) to come out of each service joint, but it's not practicable to go banging rods down in the footpath as there would be damages to other utilities and/or inadvertent cable spikings all the time!
If you believe it should be down to the DNO to provide rods at the cutout position rather than down to the electrician, it would just be added on to the price of a new connection plus their markup. And I've never heard of anyone complaining how cheap new connections are nowadays. The same goes for the argument of installing 4 core/SNE/TNS cable, it would just get added on to the new connection costs and passed on to whoever's paying for it, and if it's a developer, they'd stick it on the price of the houses they're selling, so you just end up paying for it yourself. And equally, I've not heard many people complaining at how cheap new houses are. The DNOs offer to carry out all excavation if required, but most people choose to do their own as it's cheaper. Some offer to provide meter boxes for a cost, but again most people provide their own as it's cheaper. I can't see why it wouldn't be any different for earth rods.
In WPD at least, multi occupancy buildings are supplied with SNE/TNS earthing via a 4 core cable (but with a plastic sheath so not in contact with ground like the old PILC cables). This is usually jointed on to a 3 core main though! I would imagine having a TNS system would remove the need for supplementary earth rods, admittedly I haven't read the document in any depth, but this would make dealing with flats etc much easier.
Hope this helps in some way...
I must say I find your logic somewhat ironic.
That people may consider it cheaper to fit a rod themselves, by which I presume you mean employ an electrician, could be more to do with exorbitant prices charged by the suppliers.
If electricians charged thousands then people probably would literally do it themselves.
That people may consider it cheaper to fit a rod themselves, by which I presume you mean employ an electrician, could be more to do with exorbitant prices charged by the suppliers.
If electricians charged thousands then people probably would literally do it themselves.
What people probably don't realise is the hourly rate of a contract jointer is huge, especially by the time the DNO has put their uplift on. It makes no sense to tie up a team of two to bang rods in and hang meter boxes when you're going to have an electrician there anyway to install your electrical installation, and a labourer is capable of hanging meter boxes. Then they can use the jointer for more productive tasks like another new connection.
As for what they charge, I don't really get involved with that, but broadly speaking it's not too different to other utilities.
the culture also allows for costs versus probality to affect the regulations. If the risk of an incident happening is very small and there is a cost involved in preventing it from happening then that incident may be excluded from consideration in the regulations.
If the rod has a very low impedance then the current in bonding connections during a hailed Neutral condition will be high. In a few cases high enough to cause a fire. Worst case is when a Neutral fails and the water supply is via a metallic pipe.
Another situation where ( dangerously ) high currents in bonding cables can occur is when when two properties have a common metallic service pipe ( gas, water or oil ) but are fed from different branches of the local electrical supply network. Two supply Neutrals are connected together by a low impedance path via bonding and metalic service pipes. There doesn't have to be a Neutral fault in this situations for high currents in bonding wires. A 5 volt dfference in Neutral potentials and a 0.1 ohm path is 50 amps through the bonding cables. And there is no fuse in that path between Neutrals.
- Joined
- 11 Jan 2004
- Messages
- 42,733
- Reaction score
- 2,633
- Country
I admit that I have not read all of the comments in this thread so to date.
However, may I draw your attention to
"Grounding - Safety Fundamentals" at
It is my understanding that the reason for installing a "local earth electrode" at any structure will be found between 23:00 and 28:30 (with some important continuation to 33:00) of this video.
The “System Protection” provided by the use of a local earth electrode/earth stake/earth rod is a path to Earth for any High Frequency DC Pulse due to lighting activity.
Because of this, the (Low) Impedance of the Earthing Path is vastly more important than the Resistance to Earth at the local earth electrode.
To limit the imposed voltage, the grounding electrode conductors should not be any longer than is necessary and unnecessary bends and loops should be avoided.
For this reason, https://commons.wikimedia.org/wiki/File:HomeEarthRodAustralia1.jpg actually shows an example of how NOT to wire a “Local Earth Electrode”.
(A local earth electrode is NOT a protection against a direct lightning strike NOR is it for "Equipment Protection".)
However, may I draw your attention to
"Grounding - Safety Fundamentals" at
It is my understanding that the reason for installing a "local earth electrode" at any structure will be found between 23:00 and 28:30 (with some important continuation to 33:00) of this video.
The “System Protection” provided by the use of a local earth electrode/earth stake/earth rod is a path to Earth for any High Frequency DC Pulse due to lighting activity.
Because of this, the (Low) Impedance of the Earthing Path is vastly more important than the Resistance to Earth at the local earth electrode.
To limit the imposed voltage, the grounding electrode conductors should not be any longer than is necessary and unnecessary bends and loops should be avoided.
For this reason, https://commons.wikimedia.org/wiki/File:HomeEarthRodAustralia1.jpg actually shows an example of how NOT to wire a “Local Earth Electrode”.
(A local earth electrode is NOT a protection against a direct lightning strike NOR is it for "Equipment Protection".)
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
