External earth fault loop tt system

[Geordie Spark]

So tell me, what do you think gives a DNO Distribution Transformer it's earth and it's TN-S cables earth and PME / (TNC-S) neutral conductors it's multiple earthing then?? lol!!

A local stable TN value TT system is better to have, than a supplied TN earthing system. You are in control of that system not others!! Yet many of you scoff at the idea as not being possible, when in fact it's more than just possible!! Though you certainly wouldn't think so, going by this thread and the ''why bother'' attitude!!

The seemingly total lack of understanding towards TT systems in the UK these days, is just amazing!!

THAT is exactly what the lecturer at the college said when I was doing the 2391 course.

Then he spoiled it by saying if you're fitting an outside halogen floodlight which has to be earthed and there's no cpc in the cable, you can link the earth terminal to the neutral at the light ............

 

[Engineer54]

THAT is exactly what the lecturer at the college said when I was doing the 2391 course.

Then he spoiled it by saying if you're fitting an outside halogen floodlight which has to be earthed and there's no cpc in the cable, you can link the earth terminal to the neutral at the light ............

They always spoil things!! Why would you even think about installing a circuit without a CPC these day's!! lol!!

 

[Deleted member 9648]

Haha, wonders never cease to amaze me!!

So what are you saying here, that a project's TT earthing system is different in importance to that of one of your domestic customers (and i'm not talking about sheds!!)?? No way on this earth would i ever see the type of light yor talking about!!

Of course your happy to conform to BS7671, it means you don't have to think about anything or come to that do much about anything either. So in your world an existing useless 700 ohms is worth changing to an equally usless 200 ohms because it says so in the Regs,yep and all because you have an RCD in place??yep Which just about sums up your argument!! That and this existing 700 ohm being perfectly safe, yeah right!! yep Why even consider the fact that the all singing, cover all RCD is going to fail sooner, rather than later....nope

Can't really be arsed anymore, you'll only come up with another smart arsed reply yep that is just going to be, yet another compromise for a working TT systemnope. I'm just wondering if you have ever installed any TT system with a sub 1 ohm or TN valuenope, perhaps before RCDs became the norm?? Probably not, definately not as you still wouldn't see the point and come up with some compromise or other!!yep
Come to that, Do you really install an S type up front on your TT installations??new ones...yep Because from your posts on this thread, Frankly i can't really see you bothering, and just using them as an example, to get over the other argument, of totally relying on a single RCD sitting on a numbty Ra value!!

lol..........

 

[Engineer54]

new ones...yep

Nope, i doubt that very much!!

Wind up merchant, nothing more, nothing less!! lol!!

 

[D Skelton]

They always spoil things!! Why would you even think about installing a circuit without a CPC these day's!! lol!!

Many reasons, the biggest one I can think of being distance.

 

[Engineer54]

Many reasons, the biggest one I can think of being distance.

Think your talking at cross purposes!! lol!!

 

[D Skelton]

I guess lol. Erm, ok, there's not very likely to be a reason to install a cable with no CPC in a domestic. How's that

 

[Engineer54]

I guess lol. Erm, ok, there's not very likely to be a reason to install a cable with no CPC in a domestic. How's that

Well, we were talking about a domestic!! But then why would you install a cable(s) that didn't include a CPC??

 

[D Skelton]

Well, we were talking about a domestic!! But then why would you install a cable(s) that didn't include a CPC??

One example would be where the distance would dictate a CPC being unreasonably enormous. We're talking miles, not meters lol.

There are many other situations where relying on ADS would not be the best option.

 

[Stroppy]

So tell me, what do you think gives a DNO Distribution Transformer it's earth and it's TN-S cables earth and PME / (TNC-S) neutral conductors it's multiple earthing then?? lol!!

A local stable TN value TT system is better to have, than a supplied TN earthing system. You are in control of that system not others!!

Good point, I hadn't thought that far ahead. Was just having a rant. I don't think we did distribution transformers on my 5 week course, although that may have been in the two weeks I was off having it large in Ibiza. Can't have missed that much.

On a serious note, the DNO is responible for getting current to and from the installation (Line and Neutral) so why shouldn't they also be responsible for the fault current path as well?

 

[Engineer54]

Good point, I hadn't thought that far ahead. Was just having a rant. I don't think we did distribution transformers on my 5 week course, although that may have been in the two weeks I was off having it large in Ibiza. Can't have missed that much.

On a serious note, the DNO is responible for getting current to and from the installation (Line and Neutral) so why shouldn't they also be responsible for the fault current path as well?

They are, where they provide an earthing point!! Sometimes the system just cant take any more end user PME connections. It's not always as simple as it first seems, and why you should always ask the DNO, if a PME connection is available. And more importantly, why you should never make your own PME connection, even if you know your next door neighbours on either side has been provided with a PME connection!!

 

[R G]

Having worked for one of the RECs and got involved with supply and distribution the pme system is the preffered system used at all times by them , you will probably notice more and more overhead TT systems being converted with the new aerial buched conductor(ABC) network , you will also probably have noticed that every 4th pole as required by Distribution Supply regs that the neutral is bonded down to earth with a stake , this is for safety reasons in case the neutral breaks down , There are drawbacks of course firstly the need to test for polarity on the incomming supply and also the loss of the neutral on the incoming supply , and the consequences. But there is no difference whether there are 10 or 100 properties being supplied , as long as the Ze is below the 0.35 . The fault current that returns back to the transformer is no longer fault current from the cut out back to the Tx , only within the customers premises , Yes it is correct that the REC would need to be contacted if you want a PME conversion , you can not do it yourself , but as time goes by more and more of the old TT systems will be converted , Indeed many olde

 

[Engineer54]

Having worked for one of the RECs and got involved with supply and distribution the pme system is the preffered system used at all times by them , you will probably notice more and more overhead TT systems being converted with the new aerial buched conductor(ABC) network , you will also probably have noticed that every 4th pole as required by Distribution Supply regs that the neutral is bonded down to earth with a stake , this is for safety reasons in case the neutral breaks down , There are drawbacks of course firstly the need to test for polarity on the incomming supply and also the loss of the neutral on the incoming supply , and the consequences. But there is no difference whether there are 10 or 100 properties being supplied , as long as the Ze is below the 0.35 . The fault current that returns back to the transformer is no longer fault current from the cut out back to the Tx , only within the customers premises , Yes it is correct that the REC would need to be contacted if you want a PME conversion , you can not do it yourself , but as time goes by more and more of the old TT systems will be converted , Indeed many olde

Go and ask your Engineer if that is always correct or not!! You may be very surprised by the sound of it!! lol!! Think you must have been working on relatively all new PME installations, and not on existing converted cables that are in excess 60+ years old!! Most of the older TN-S cables that are now beginning to breakdown haven't been completely converted either, many being over the 0.35 ohm, and also carrying TN-S earthing on sections of the same cable!!

I can think of a few valid reasons for the DNO to refuse connection to a PME converted supply, as well as too converted overhead systems as well!!

 

[R G]

TN-S systems mostly remain TN-S systems , what we are talking about here is a TT system!!
The older TT systems that are converted are allways assesed and Ze readings taken into account before conversion . Their are exceptions where even with a PME supply you would have to install your own earthing system of course!!

 

[D Skelton]

Got to agree with Eng that TT is by far the most reliable method of earthing. Disregarding the Ra value and the reliance on RCDs argument. The only thing you are relying on is the earthing arrangement at the sup tranny. No supply cable breakdown to worry about at all!

 

[R G]

Yes your right of course you do have more control of your earth arrangements . It is not unknown for neutral faults to come about on PME systems , sometimes actually melting the bonding cables and taking out appliances in some instances , I have seen it a few times

 

[Deleted member 9648]

Nope, i doubt that very much!!

Wind up merchant, nothing more, nothing less!! lol!!

Are you accusing me of lying?...:toetap05:

 

[Engineer54]

TN-S systems mostly remain TN-S systems , what we are talking about here is a TT system!!
The older TT systems that are converted are allways assesed and Ze readings taken into account before conversion . Their are exceptions where even with a PME supply you would have to install your own earthing system of course!!

I think you should really go and talk to your Engineer if you are really being serious about older DNO TN-S supply distribution cables remaining TN-S!! So what do you think the DNO's do when the lead sheathing of these old cables starts breaking down, ....dig it all up and replace them?? I would confidently say there are more partially converted TN-S cables throughout the UK than fully converted!!


Yes the thread were on, is about TT systems. But you made a post statement that isn't correct, (as you have done again in this post too!!) so i've replied!! Actually, an overhead PME system either converted or purpose installed, will probably all be full blown PME supplies, as they are much easier and cheaper to PME!!

 

[Engineer54]

Are you accusing me of lying?...:toetap05:

Maybe i wouldn't go as far as that!! But a wind up merchant, you most definitly are!! lol!!

 

[SYKRAPS]

Just read this thread from start to finish and IMO I think that it will be very useful to many people as an informative and well constructed debate........well done to 'most' involved