Benefits of a TT system?

[Crosswire]

If an installation is supplied by a two wire system (E.G. a TT system) , what are the benefits of using an earth electrode instead of simply joining earth to neutral at the supply head to create a TNCS system?

Surely using the supplier's neutral is a more effective return path for fault current than relying on the earth electrode and the solid mass of earth?

All replies welcome,

Cheers,
Crosswire.

 

[R G]

Have experienced the Neutral fault on TNCS system a couple of times with a DNO and its not pretty , with return currents from other properties returning through the bonding of the house with least resistance via the plumbing and taking out various appliance , TNCS systems have the neutral bonded down at various intervals usually every fourth pole on overheads , but quite often when the cables are below ground feeding estates this gets overlooked as cables are unseen , and thats where these faults were on joints in newly built estates .

 

[Crosswire]

Crosswire that is effectively what IS done, the bonds to the gas and water, although no one will admit it, act as back up TT rods (obviously only if metal).

Almost every time I have found a half decent TT reading, it is due to the parallel paths to these services, not the electrode itself.

Very true, despite the fact that the regs expressly forbid using incoming services as a means of earthing.
Would I be correct in thinking that a proportion of fault current would travel through the the bonds to gas and water, in the event of an earth fault, as they are connected to the fault current return path?

Didnt see above post before replying

*Edit* Also the Ze should be measured with the main incoming earth disconnected from the installation , so as to avoid the parrallel paths described above. In reality however, fault current occurs with the incoming earth connected.

 

[DPG]

Although I'm assured by my learned friends here that it does happen I've not seen a failed neutral on a TN in my 34 years in the trade. I've seen whole cables fail but not just the N.
Some countries do exactly what you're talking about so maybe it would be a good idea if it were adopted here. Would I do it? Probably not

Seen it twice, once on my own house. Both times it was the joint under the pavement where the house was tapped off. Spoke to the jointers who said it's not at all uncommon. Poor quality 1970s joints maybe? Daz

 

[DPG]

:sifone: Unlike the 60s joints which were apparently much better :sifone:

 

[telectrix]

was a much better quality grass in the 60's. i blame the EU for allowing imports of sub-standard pot.

 

[Geordie Spark]

:sifone: Unlike the 60s joints which were apparently much better :sifone:

I can't say I remember.

 

[telectrix]

geordie. forgot to thank you last week for giving me my 20,000th like.

 

[Geordie Spark]

geordie. forgot to thank you last week for giving me my 20,000th like.

You're welcome.

 

[SPARTYKUS]

Mrs Trev makes a fantastic bacon sarnie

White bread?

 

[trev]

We get a choice, white, brown or buns
Spoilt rotten

 

[Geordie Spark]

White bread?

White bread?? ....Hadawayanshyte!!

Stotty cyeke bonny lad .... Mrs. Trev's a Geordie lass.


Stottie cake - Wikipedia, the free encyclopedia

 

[Silly Sausage]

Baps, barms or rolls (crusty or soft), the choice is endless!

Devil's Bridge is a fine place for a bacon butty and tea.

 

[R G]

We get a choice, white, brown or buns
Spoilt rotten

Must say I like a nice pair of Buns ,,,:sifone:

 

[trev]

White bread?? ....Hadawayanshyte!!

Stotty cyeke bonny lad .... Mrs. Trev's a Geordie lass.


Stottie cake - Wikipedia, the free encyclopedia

The thing is Geordie, with the death of the small local bakers the only stotty that's available now is from Greggs. Have you tasted that crap? It really is vile, it's just a disc of bland stodge.
I'm going to go look up a recipe for it and try making some.

 

[Geordie Spark]

The thing is Geordie, with the death of the small local bakers the only stotty that's available now is from Greggs. Have you tasted that crap? It really is vile, it's just a disc of bland stodge.
I'm going to go look up a recipe for it and try making some.

Yep .... tell me about it!

As for ASDA's bread .. let's not even go there.