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Topic Title: Neutral is re-earthed in the control panel
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Created On: 14 July 2012 05:11 PM
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 14 July 2012 05:11 PM
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Glendower

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I have bought a house in Bulgaria which needs to be rewired

I have been doing a bit of research into how the electrics should be wired in Bulgaria and came across this useful PDF document by Legrad, 'International electrical
standards & regulations', Link removed/files/fck/F...uide-International.pdf

It appears that Bulgarian wiring should be done in accordance with German regulations see page 4. Pages 14-21 give the information regarding the German regs.

I have only seen a little of electrics in Bulgaria but they do not appear to adhere to any of the earthing requirements? As I want to do my property as per the regs I will be making sure it is earthed correctly.

In regard to earthing I have a question that someone may be able to help me with and that is on page 16 is says "Neutral is re-earthed in the control panel". Can anyone explain what this means please?
 14 July 2012 05:56 PM
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david911cockburn

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When I worked in Germany the available supply was just a line and neutral.
Therefore I wired my system as normal and simply connected my earth to the supply side of the neutral.
The RCD main switch and the MCB's worked fine as you would expect them to.
In short, create your own PME system.
 14 July 2012 08:46 PM
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dickllewellyn

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I think I'd rather put a rod or two in!

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Richard (Dick)

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 14 July 2012 09:42 PM
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postman

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Originally posted by: david911cockburn

When I worked in Germany the available supply was just a line and neutral.

Therefore I wired my system as normal and simply connected my earth to the supply side of the neutral.

The RCD main switch and the MCB's worked fine as you would expect them to.

In short, create your own PME system.


What's going to happen if you have a heavily loaded Neutral?
The Neutral voltage will rise substantially above zero volts and so will all your metalwork.
And what about losing the supply Neutral?

It's dangerous to simply bond your Earth to your Neutral.

Edited: 14 July 2012 at 10:10 PM by postman
 15 July 2012 07:55 AM
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gkenyon

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Originally posted by: postman
What's going to happen if you have a heavily loaded Neutral?

The Neutral voltage will rise substantially above zero volts and so will all your metalwork.

And what about losing the supply Neutral?



It's dangerous to simply bond your Earth to your Neutral.
Let's get rid of PME then !

-------------------------
Eur Ing Graham Kenyon CEng MIET TechIOSH
 15 July 2012 09:47 AM
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postman

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Originally posted by: gkenyon
Let's get rid of PME then !


That's not what I mean.

With PME in the UK you can pretty much guarantee the Neutral is held at ground potential because it is rodded at various points.

We are talking about Bulgaria here, can you guarantee that the Neutral cable has any earthing at all?

What David is recommending is to connect all the metal work in a property to the Neutral cable without knowing if the Neutral is grounded.
 15 July 2012 10:11 AM
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daveparry1

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without knowing if the Neutral is grounded
-------------------
I could hardly believe he said that Postman considering all the other stuff he's posted about electrical safety etc!

Dave.
 15 July 2012 10:18 AM
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ebee

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That there new fangled PME theory will never catch on!
None of us would be daft enough to walk around on a live conductor.



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Ebee (M I S P N)

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 15 July 2012 11:53 AM
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rocknroll

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I would like to point out that a lot of countries have the arrangement where they supply you with a live and a earthed neutral and unlike us you are required to make the earth/neutral connection within the consumer unit.

Generally under their wiring rules you are also required to connect an earth rod to the neutral bar as well, to ensure safety we often connect heavy current using equipment like water heaters, cookers, A/C etc; to an earth rod but be aware a lot of countries wiring rules prohibit the use of TT.

The whole question of the continued use of TT as we now live in a world of earthed neutral is under scrutiny by the IEC 60364 committee who have not met properly for 30 years, there is a big meeting that is likely to stretch over 2014/2015 and rumour has it will involve the NEC to discuss the continued use of TT or not, the general feeling by engineers is that it should be prohibited because of concerns of safety but that will be advice and it is up to the individual countries own wiring rules bodies to decide on this.

If you are wiring a house in another country you need to forget BS7671 and concentrate and study the local wiring rules and building codes as should something happen and you have not followed that nations rules there could be consequences, like insurance for instance.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 15 July 2012 at 12:16 PM by rocknroll
 16 July 2012 09:12 AM
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broadgage

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In many countries, the electricity supply consists of a live and and allegedly/hopefully earthed neutral.
In many such countries, the usual practice is that the consumers installation has live, neutral, and earth wires. The protective earth is obtained by connecting together the earth and neutral bars in the consumer unit.
It is allways good practice, and often a requirement, to also connect an earth rod to this neutral/earth connection.

This is very similar in principle to our PME system, the main difference being that the earth is connected to the suppliers neutral within the consumer unit, rather than within the suppliers cut out.
 16 July 2012 10:22 AM
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Parsley

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The whole question of the continued use of TT as we now live in a world of earthed neutral is under scrutiny by the IEC 60364 committee who have not met properly for 30 years, there is a big meeting that is likely to stretch over 2014/2015 and rumour has it will involve the NEC to discuss the continued use of TT or not, the general feeling by engineers is that it should be prohibited because of concerns of safety but that will be advice and it is up to the individual countries own wiring rules bodies to decide on this.

RnR that's interesting,and seems to be the opposite of what the engineer's at schneider thought was going to happen when they predicted the increased use of TT in the mid 90's.

Regards
 16 July 2012 12:27 PM
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rocknroll

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Originally posted by: Parsley

The whole question of the continued use of TT as we now live in a world of earthed neutral is under scrutiny by the IEC 60364 committee who have not met properly for 30 years, there is a big meeting that is likely to stretch over 2014/2015 and rumour has it will involve the NEC to discuss the continued use of TT or not, the general feeling by engineers is that it should be prohibited because of concerns of safety but that will be advice and it is up to the individual countries own wiring rules bodies to decide on this.

RnR that's interesting,and seems to be the opposite of what the engineer's at schneider thought was going to happen when they predicted the increased use of TT in the mid 90's.

Regards


Ever since 1984 when 99% of the country was PME'd right up to the substations and various engineering documents relating to global earthing were put forward by the DTI the TT vs TN debate has flourished and no matter what is decided in the future the debate will no doubt continue.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 16 July 2012 01:30 PM
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timothyboler

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From what I understand the American system is as described above by Rock and Broadgage. A typical house has 2 or 3 "service conductors" comprising of 1 or 2 being "ungrounded service conductors" (line) and 1 "grounded service conductor" (neutral).

At the customer's premises the supplier's "grounded service conductor" (neutral) has to be re-grounded at the first disconnecting means by use of an earth electrode connected to the neutral bar. The neutral bar is connected to the earth bar via a "main bonding jumper" (neutral earth link). From here the neural and earth split and serve the installation.

In IEC terminology this is in effect a TN-C-S (PME) system with an additional mandatory earth electrode at the customer's service disconnecting means. But note there is no requirement for the earth electrode to have any minimum resistance or any requirement to test it - just a minimum of 8ft depth (for a rod for example).

In contrast to IEC the American NEC does not recognize TT as an earthing system. A fundamental requirement of their low-voltage electrical system is that there is a low impedance path for fault current back to the source and it explicitly states that "the earth shall not be considered as an effective fault - current path".

This PME type set-up mandatory even for agricultural buildings however additional earth electrodes are required at each and every outbuilding and "equipotential planes" are required to be installed in some locations e.g. where accessible to livestock.

The question is which system is best? I'm not sure but I'll take a stab by saying that the chance of a disconnected neutral only and not the line at the same time is pretty slim; probably significantly slimmer than a faulty RCD plus earth fault. The British gave the green light to PME (following the German system) after 10 years of careful consideration during the 1950s so it would be a bit of a U-turn to go back now.

Regards, Tim

-------------------------
Everyone loves a fireman - but hates the fire inspector.
 16 July 2012 03:57 PM
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jcm256

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While you are on earthing systems debate, what is the advantage of this system?

Based on BS7671 wiring regulations the Abu Dhabi wiring regulations use a system called (TN - S - TT):
A system of supply where the Distribution Company provides an Earth connection to the Customer's Main Earth Terminal and a local Earth provided by the Customer is also connected to the same MET, having an Earth Resistance value of not more than 10 Ohm
The preferred earthing system to be used in Abu Dhabi Emirate is TN-S-TT. However, either TN-S or TT systems may be used

Earth fault current shared between Customer Earth Electrode and Distribution Company Earth Earth sheath or armour of Distribution Company Cable is connected to Customers Installation Transformer Neutral Point Earth Customer's Earth Electrode Main Earth Terminal Customer's Main Distribution Board


Components of earth fault loop impedance

X
Internal earth loop impedance

1 Impedance of Circuit phase conductor
2 Resistance of fault
3 Impedance of Circuit Earth Conductor (CEC)
4 Impedance of Local Earth Electrode
5 Impedance of fault path through ground

Source earth loop impedance, Ze

6 Impedance of transformer neutral earth point
7 Impedance of network cable earth conductor / armouring
8 Impedance of network cable earth conductor / armouring
9 Distribution Company transformer winding
10 Live conductor of distribution network cable
11 Live conductor of Supply cable


http://www.scribd.com/doc/6093...lctricity-Wiring-Rules
 16 July 2012 04:34 PM
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kj scott

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Originally posted by: timothyboler

The question is which system is best? I'm not sure but I'll take a stab by saying that the chance of a disconnected neutral only and not the line at the same time is pretty slim; probably significantly slimmer than a faulty RCD plus earth fault. The British gave the green light to PME (following the German system) after 10 years of careful consideration during the 1950s so it would be a bit of a U-turn to go back now.

Regards, Tim


Loss of neutral conductor only, is not so rare in rural LV overhead lines, where the neutral is the lowest of the conductors; although the distributors would have us believe otherwise.

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 16 July 2012 05:33 PM
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Parsley

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Originally posted by: rocknroll

Originally posted by: Parsley



The whole question of the continued use of TT as we now live in a world of earthed neutral is under scrutiny by the IEC 60364 committee who have not met properly for 30 years, there is a big meeting that is likely to stretch over 2014/2015 and rumour has it will involve the NEC to discuss the continued use of TT or not, the general feeling by engineers is that it should be prohibited because of concerns of safety but that will be advice and it is up to the individual countries own wiring rules bodies to decide on this.



RnR that's interesting,and seems to be the opposite of what the engineer's at schneider thought was going to happen when they predicted the increased use of TT in the mid 90's.



Regards




Ever since 1984 when 99% of the country was PME'd right up to the substations and various engineering documents relating to global earthing were put forward by the DTI the TT vs TN debate has flourished and no matter what is decided in the future the debate will no doubt continue.



regards


For sure!

I thought the post was about the different types of earthing used throughout the world not just the UK.

I think the Schneider engineer's were concerned about high fault currents, EMC, harmonics and the associated damage to electronic equipment. They show a hybrid of TN-S/TT with the link from the neutral TX to earth through an impedance to reduce the fault current and damage to electronics and in theory reducing EMC issues because there's no PEN conductor used in the distribution.

Regards
 16 July 2012 08:34 PM
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timothyboler

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Originally posted by: jcm256

While you are on earthing systems debate, what is the advantage of this system?

Based on BS7671 wiring regulations the Abu Dhabi wiring regulations use a system called (TN - S - TT):


I can't really see the purpose of this system. The additional earth electrode at the installation has no bearing on the neutral like in a PME system as the earth and neutral are already isolated before the installation. Only if the supplier's earth was disconnected, broken, or never connected :-s would the electrode provide a backup current return path to operate an RCD. Would be wishful thinking for other protective devices though.

In any case the nomenclature of TN-S-TT is misguided as a true TT system has the installation electrode earth electrically separated from the suppliers earth i.e. the only electrical connection between source earth and installation earth is through the ground. In fact the double 'T' makes no sense either as the first letter should represent the means of earthing at the source.

In essence what the Abu Dhabians have here is simply a TN-S with an extraneous conductive part (in the form of an earth rod) bonded to the main earthing terminal.

Regards, Tim

-------------------------
Everyone loves a fireman - but hates the fire inspector.
 16 July 2012 09:08 PM
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timothyboler

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Originally posted by: kj scott

Loss of neutral conductor only, is not so rare in rural LV overhead lines, where the neutral is the lowest of the conductors; although the distributors would have us believe otherwise.


Good point and I guess could affect multiple customers at the same time. Probably best then that we're flexible and utilize both systems; like rings and radials You'd be hard pushed to say that one is inferior to the other (although people will try).

Regards, Tim

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Everyone loves a fireman - but hates the fire inspector.
 17 July 2012 01:08 PM
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AJJewsbury

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In any case the nomenclature of TN-S-TT is misguided

Agreed. Although I can perhaps see some value in multiply earthing a TN-S system in a country where maintaining a good earth must be difficult (e.g. if the water table under the substation drops leaving the rod in little more than dry sand) - having a few hundred 'backup' electrodes on the system seems sensible.
- Andy.
 17 July 2012 02:13 PM
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ebee

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if we ever ask "the board" for a Ze strangely they always seem to quote 0.3 anywhere in three main towns I work in for TNS.

We usually measure it at around 0.24 or 0.23.

Who is to say it is not nearer 0.3 in reality and all the bonding etc of neighbouring properties is not pulling it down a little even though our own bonds are disconnected?

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
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