Neutral link to earth

[rantoftheday]

Can someone tell me why on certain installation where a main earth ain't in place ie domestic property why can't an earth be taken off main incoming neutral as a tn-c-s system instead if installing a tt system?

 

[trev]

To system? I'm guessing you mean TT mate but please clear that up.

In a lot of cases the DNO does not supply an earth facility, this is why TTs exist because if an earth is not supplied it has to be put in place by us. DIY TN-C-S systems are not the way forward

 

[rantoftheday]

Sorry yes TT system

 

[rantoftheday]

But effectively would a tn-c-s system installed by a qualified spark not work as well, if not better than a TT system? Plus saves the hassle of putting in earth rod(s) running cables to db and putting in type s RCD etc

 

[Sintra]

The DNO have to convert to a TN-C-S how does a spark coming into a job know if PME is available. There is more to it than just joining N&E together in the service head.

 

[trev]

It may well work better than a TT mate but what you have to remember is that if you do a DIY TN-C-S you're messing with the DNOs toys. If anything were to go wrong with it it's going to be you that's in a big wooden panelled room with blokes in wigs explaining why you did what you did when you had no right to do that. On the other hand it may not work well at all and you could fry people.
Is it really that difficult to install a decent rod system? I'd say not. It's always worth a call to them to see if PME is available in a particular area but sometimes you're going to be told no in which case, since you're the apprentice hehe, you'd best get swinging that hammer

 

[rantoftheday]

Great reply trev. Tbh it was purely a curiosity question. I don't swing hammers no more mate we have a younger apprentice now ha. By the looks of your pic been a while since you've been swinging hammers! Unless your the little un in the pic! Ha cheers for the answer buddy all the best

 

[rantoftheday]

Why and how do they convert for a tncs Sinatra?

 

[Sintra]

The DNO will only convert if PME is available externally. PS people have been banned for calling me Sinatra :lol:

 

[trev]

It's always good when a newer apprentice turns up because he then gets the crappier jobs which you used to enjoy so much, sadly now I'm self employed I have to do all the hammer swinging, and the bloody sweeping up, getting the sarnies....bloody hell it's like a second childhood
No mate, the little un in the pic is my grandson and newset apprentice, 2 years old come Monday and he was "helping" me with a couple of jobs round the house today.

 

[Sintra]

The additional source earths are what need to be installed before a system can be changed to TN-C-S

 

[Darkwood]

If you combine earth to neutral on a standard TT system it will work fine and dandy but under certain fault conditions it can be lethal - - -a neutral break anywhere on the supply cable could make all the earthed metalwork live....
Hence a very dangerous situation for everyone.....
When they convert a TT to TNCS they strap N to earth at every available point hence PME stickers 'Protective MULTIPLE Earthing'.... this in turn gives a very low risk that the return N/E path is lost ever as a break will have multiple return options.


As Sintra says there is alot more to it than even i have explained but it shows how dangerous converting it yourself can be as well as illegal.

 

[trev]

If you can aprenticesprky, print out that diagram that Frank posted. It's one of the best pictorial explanations I've seen of a TN-C-S earth path in a long time.
I'll see you after me ban expires

 

[rantoftheday]

Sorry sintra it's self correcting text and never noticed didn't realise it was frank. Trev, ill bet your 2 yo grandson is more competent than some of my journeymen. Ps good diagram

 

[trev]

Sorry sintra it's self correcting text and never noticed

Good save mate, I'll try that one meself sometime cheers

 

[Sintra]

If you can aprenticesprky, print out that diagram that Frank posted. It's one of the best pictorial explanations I've seen of a TN-C-S earth path in a long time.
I'll see you after me ban expires

This one shows the fault path.

 

[rantoftheday]

Sintra do you have guidance notes in electronic format?

 

[Sintra]

Sorry sintra it's self correcting text and never noticed didn't realise it was frank. Trev, ill bet your 2 yo grandson is more competent than some of my journeymen. Ps good diagram

Could be 2 for the :ban: hammer tonight :lol:

- - - Updated - - -

Sintra do you have guidance notes in electronic format?

I sure do

 

[rantoftheday]

Are they available to buy in e format? Where can I purchase? Kindle?

 

[Sintra]

You can get the full package from the IET for £215.00 should work on kindle through vital source bookshelf.

IET Wiring Regulations BS 7671:2008(2011)
Guidance Note 1: Selection & Erection
Guidance Note 2: Isolation & Switching
Guidance Note 3: Inspection & Testing
Guidance Note 4: Protection Against Fire
Guidance Note 5: Protection Against Electric Shock
Guidance Note 6: Protection Against Overcurrent
Guidance Note 7: Special Locations
Guidance Note 8: Earthing & Bonding
On-Site Guide
Electrician’s Guide to the Building Regulations
Electrical Installation Design Guide: Calculations for Electricians and Designers (new edition to be added upon publication, late 2012)

Wiring Regulations Digital - Business Package - IET Electrical