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@Megawatt as already said, in the UK only the supply authority (DNO) is allowed to bond N & E together for various safety reasons, largely to do with the consequences of an open 'neutral' making metalwork live, and to limit spurious current circulating around the earthing structures of multiple buildings, etc.

It is common in the UK for the bond point to be at the supply cut-out and that is called TN-C-S here (Common N & E to the supply point, Separate after) but within any normal installation N & E will not be bonded together. In this case the DNO is expected to have multiple low-impedance earth rods at points along the conductor (hence the PME name given for protective multiple earth). That is not always successful, and there are PME faults putting folk at risk disturbingly often across the UK.

The main advantage is to save conductor costs over the traditional TN-S system by not running separate N & E to everywhere (secondary advantage is usually a lower supply fault impedance Ze so easier to achieve fast disconnection by fuse or MCB).

The main disadvantage is the PME open-circuit fault consequences that are comparable to the TN-C risk of metalwork going live and high currents flowing in to anything bonded to true Earth (e.g. metal water pipes, etc).

There was talk of having UK properties being fitted with earth rods for TN-C-S as they are built, etc (which I think is similar to the USA arrangement) but they would go to the 'E' after the DNO point in any case (which is not isolated by incoming switch, etc) and definitely not to N. But that has not made it in to our regulations yet.

Of course with a TT setup you only have the rod(s) for earth and so in practice you need RCD protection for all circuits to have any real hope of disconnecting on a fault as it is really hard to get below ten-ish ohms for a couple of rods, and you really need one ohm or below in many cases.

"There was talk of UK properties being fitted with earth rods for TNCS as they are built. But that has not made it into our regulations yet"

It never will, it contravenes the ESQCR (real) regulations.
 
"There was talk of UK properties being fitted with earth rods for TNCS as they are built. But that has not made it into our regulations yet"

It never will, it contravenes the ESQCR (real) regulations.
In what way?

After all the practical effect (a local earth supplementing the supply) is no different from bonding to metal service pipes.
 
In what way?

After all the practical effect (a local earth supplementing the supply) is no different from bonding to metal service pipes.

Its a long story, and i dont get involved in long stories, but it was yet another hairbrained scheme dreamt up by the BS7671 picture guidance book to "improve" our network. Perhaps they should remind themselves of the scope of the regulations. Distribution/supply is out of scope of the regulations.
 
Its a long story, and i dont get involved in long stories, but it was yet another hairbrained scheme dreamt up by the BS7671 picture guidance book to "improve" our network. Perhaps they should remind themselves of the scope of the regulations. Distribution/supply is out of scope of the regulations.

But how will it contravene ESQCR?
 
I want to ask now. Why is TN-S being phased out? What was the technical justification for abandoning a previous method that worked better?
Cost.

Remember their cost decision is about delivering power, not considering the implications for more expensive EV chargers, etc., for those using the power.
 
Yes, but I don't think TNCS had been thought of at that time.
What's not to think of? All supply systems are relatively simple to design and weigh up regarding pro, s and cons. TNC-S as, a supply system has been there as long as the others but can you imagine been the electrical engineer who suggested it....
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Cost.

Remember their cost decision is about delivering power, not considering the implications for more expensive EV chargers, etc., for those using the power.
Agreed. It was an economic decision. Very smart in the short term but long term........ (sighs!!)
 
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Thinking about it a little, put yourself in the shoes of those running the distribution networks "a few years back". AIUI they typically didn't provide an earth, so the distribution network was 4 core, and 2 core to the single phase customers.
Then along came plastic gas and water pipes. Customers (or their electricians, or the builders putting houses up) had become used to having a solid earth via the water supply - and this was becoming an unknown factor. At the same time I suspect, people were starting to think more about safety - and just banging a token rod in the ground was no longer acceptable for installation earthing.
So "people" start looking to the DNOs and asking why there's no earth being provided, and at some point (AIUI) the DNOs were told they had to start providing earths. Logically, it's the place to provide an earth - they have long runs of underground cable (which at the time would have been mostly lead sheathed), and for overhead supplies they have plenty of poles they can put an earth rod in close to to make a distributed earthing system.
Where they have 4 core lead sheathed in the ground, it's easy to provide an earth - but there's no guarantee that the sheaths are electrically linked at every joint. If it's not got a conductive sheath then that's a different matter. And overhead supplies would have been typically two or four uninsulated cores strung from pole to pole. So what are they supposed to do in these situations ?
Overhead they could string another wire - as long as none of the spans are marginal for height. But if there's an insulated underground section then the only way to add an earth core would be to start digging. And in urban areas with typically underground supplies, that's a lot of digging to do. Basically, adding a separate earth to sections of the network that don't already have one is a massively expensive task.

So if you look at the cost involved of providing a separate earth across the network, you can understand why combined N&E looked attractive. And even when building a new bit of network, you've eliminated a 5th core - which even allowing for it perhaps being a smaller CSA, is a big saving in copper.
And if you have (e.g.) lead sheathed cables in the ground, just linking the neutral to sheath at some joints immediately gives you a strong earth - without having to go round checking for sheath bonding across all joints.
 
Thinking about it a little, put yourself in the shoes of those running the distribution networks "a few years back". AIUI they typically didn't provide an earth, so the distribution network was 4 core, and 2 core to the single phase customers.
Then along came plastic gas and water pipes. Customers (or their electricians, or the builders putting houses up) had become used to having a solid earth via the water supply - and this was becoming an unknown factor. At the same time I suspect, people were starting to think more about safety - and just banging a token rod in the ground was no longer acceptable for installation earthing.
So "people" start looking to the DNOs and asking why there's no earth being provided, and at some point (AIUI) the DNOs were told they had to start providing earths. Logically, it's the place to provide an earth - they have long runs of underground cable (which at the time would have been mostly lead sheathed), and for overhead supplies they have plenty of poles they can put an earth rod in close to to make a distributed earthing system.
Where they have 4 core lead sheathed in the ground, it's easy to provide an earth - but there's no guarantee that the sheaths are electrically linked at every joint. If it's not got a conductive sheath then that's a different matter. And overhead supplies would have been typically two or four uninsulated cores strung from pole to pole. So what are they supposed to do in these situations ?
Overhead they could string another wire - as long as none of the spans are marginal for height. But if there's an insulated underground section then the only way to add an earth core would be to start digging. And in urban areas with typically underground supplies, that's a lot of digging to do. Basically, adding a separate earth to sections of the network that don't already have one is a massively expensive task.

So if you look at the cost involved of providing a separate earth across the network, you can understand why combined N&E looked attractive. And even when building a new bit of network, you've eliminated a 5th core - which even allowing for it perhaps being a smaller CSA, is a big saving in copper.
And if you have (e.g.) lead sheathed cables in the ground, just linking the neutral to sheath at some joints immediately gives you a strong earth - without having to go round checking for sheath bonding across all joints.
I appreciate your points and likewise I appreciate the dilemma the various DNOs were presented with and obviously a, solution had to be arranged. I can, t comment on the situation in the UK but I do not believe it is satisfactory here (ROI) where it is becoming almost exclusively TNC-S to accept that we must now regard the risks associated with a broken neutral as the "new norm".
If the DNO is not for whatever reason in a position to provide a solution let's at least as an industry "front up" about the reality of the situation and start looking at ways to solve the issue from the homeowners standpoint.
I don't want to go into any detail about possible solutions, as its been discussed already extensively (and very adequately) on this and other threads. I can appreciate that there may be a degree of "fatigue" setting in. But I will say this. If I am to hear that the UK is going to follow our lead (and Aus, NZ) etc and implement the "four foot" rod (AKA "the fig leaf), I will despair ?. COOKIE, Are you out there? Time to launch a transatlantic campaign to fully TNC-S?
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I appreciate your points and likewise I appreciate the dilemma the various DNOs were presented with and obviously a, solution had to be arranged. I can, t comment on the situation in the UK but I do not believe it is satisfactory here (ROI) where it is becoming almost exclusively TNC-S to accept that we must now regard the risks associated with a broken neutral as the "new norm".
If the DNO is not for whatever reason in a position to provide a solution let's at least as an industry "front up" about the reality of the situation and start looking at ways to solve the issue from the homeowners standpoint.
I don't want to go into any detail about possible solutions, as its been discussed already extensively (and very adequately) on this and other threads. I can appreciate that there may be a degree of "fatigue" setting in. But I will say this. If I am to hear that the UK is going to follow our lead (and Aus, NZ) etc and implement the "four foot" rod (AKA "the fig leaf), I will despair ?. COOKIE, Are you out there? Time to launch a transatlantic campaign to fully TNC-S?
Sorry fourth sentence should read" NOT satisfactory"
 
I appreciate your points and likewise I appreciate the dilemma the various DNOs were presented with and obviously a, solution had to be arranged. I can, t comment on the situation in the UK but I do not believe it is satisfactory here (ROI) where it is becoming almost exclusively TNC-S to accept that we must now regard the risks associated with a broken neutral as the "new norm".
If the DNO is not for whatever reason in a position to provide a solution let's at least as an industry "front up" about the reality of the situation and start looking at ways to solve the issue from the homeowners standpoint.
I don't want to go into any detail about possible solutions, as its been discussed already extensively (and very adequately) on this and other threads. I can appreciate that there may be a degree of "fatigue" setting in. But I will say this. If I am to hear that the UK is going to follow our lead (and Aus, NZ) etc and implement the "four foot" rod (AKA "the fig leaf), I will despair ?. COOKIE, Are you out there? Time to launch a transatlantic campaign to fully TNC-S?
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Sorry fourth sentence should read" NOT satisfactory"


I'm still here! :)

See my other thread, I may have a solution for full TN-S!
 
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