# Another Question!



## Trimix-leccy (Dec 4, 2007)

*Another answer*

Not a clue! Never experienced it.
The 'source ' is either TNC-S or TN-S. Combining the neutral and earth after the metering point is a big No-No. And when it IS done it is carried out by the poco within their fuse cutout before the metering point.
So, in brief...you're on your own with this one:whistling2:. Cannot even get my head around what is happening:no:

Have you been given a 'spec' for the job / testing?? or any original paperwork / design. 

It seems a bit unfair that you are expected to inspect an alien installation in a foreign country to a set of unfamiliar and obsolete standards that has been installed in a 'less than normal' way

....rule of thumb; earth everything, bond everything, RCD everything, ground rods til you are sick of them and THEN get someone else to sign it off:laughing:


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## TheRick (Apr 13, 2008)

Trimix-leccy said:


> Not a clue! Never experienced it.
> The 'source ' is either TNC-S or TN-S. Combining the neutral and earth after the metering point is a big No-No. And when it IS done it is carried out by the poco within their fuse cutout before the metering point.
> So, in brief...you're on your own with this one. Cannot even get my head around what is happening:no:


Well at least I don't feel so bad anymore.:wallbash:



Trimix-leccy said:


> Have you been given a 'spec' for the job / testing?? or any original paperwork / design.
> 
> It seems a bit unfair that you are expected to inspect an alien installation in a foreign country to a set of unfamiliar and obsolete standards that has been installed in a 'less than normal' way


NO specs or plans or anything...the guys building it kinda threw it together on their own. The only reason they are claiming the installation was done to the British Standard now is to avoid driving ground rods at every facility (NEC requirement). We started this project inspecting to the NEC, but have now switched gears, and the contractor identifies the wiring system at each facility before I inspect. The problem arises when the contractor rep. does not even understand the NEC much less the BS.:hammer:



Trimix-leccy said:


> ....rule of thumb; earth everything, bond everything, RCD everything, ground rods til you are sick of them and THEN get someone else to sign it off:laughing:


This is the direction I am headed in...the only problem is I am the one that has to sign off on EVERYTHING!:hang:


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## nick (Feb 14, 2008)

*grounding neutral ?*

HEY RICK , what are you saying generator feeds 5 wire 3 phase to transformer step down to lower voltage to a 4 wire service ? explain tncs ? if you change voltage from higher to a lower voltage via a transformer you must ground that neutral as a new source of power like a new service. if your generator is feeding a power distribution panel first before the transformer then do not ground that neutral in that ( dist sub panel ) as this will effect the tripping of generator breaker in the event of a fault condition . but i hope i understand you and what you are trying to ask ? give more details i dont understand bs or tncs ? are these cables like cannon plugged cables or is this run in conduit it makes a bigg difference rick let us know we kind of like to help ya . best to ya


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## TheRick (Apr 13, 2008)

nick said:


> HEY RICK , what are you saying generator feeds 5 wire 3 phase to transformer step down to lower voltage to a 4 wire service ? explain tncs ? if you change voltage from higher to a lower voltage via a transformer you must ground that neutral as a new source of power like a new service. if your generator is feeding a power distribution panel first before the transformer then do not ground that neutral in that ( dist sub panel ) as this will effect the tripping of generator breaker in the event of a fault condition . but i hope i understand you and what you are trying to ask ? give more details i dont understand bs or tncs ? best to ya


No transformer involved...European style system here in Iraq, generator is 3 phase 4 or 5 wire, TN-C-S is a British 4 wire system T=Terra (earth aka ground) N= Neutral C= Combined (earth and neutral are one conductor) S= seperate (earth and neutral are seperate in the premises wiring).

The rules for bonding and grounding are considerably different in the British Standard compared to the NEC.


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## Trimix-leccy (Dec 4, 2007)

Just a thought, it may make it easier to comprehend if you remember that EVERYTHING before the *-S *is refering to the supply authorities side.

So the tncs means the suppliers side has the n and e combined [*C*] and the installation is seperate [*S*]

tns means the suppliers side n and e AND the installation n and e are seperate [*S*]....see, told you so! clear as mud!!:laughing:


I reckon that somebody installed the wrong cable at some time [not enough cores....you do know that we use the armouring of Steel Wire Armoured cable as the earth? along with a supplement if required] and thought they would strap N and E together as a 'get-out'


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## TheRick (Apr 13, 2008)

Trimix-leccy said:


> I reckon that somebody installed the wrong cable at some time [not enough cores....you do know that we use the armouring of Steel Wire Armoured cable as the earth? along with a supplement if required] and thought they would strap N and E together as a 'get-out'


They used the steel wire armour cable in some areas...in others no armour, where they used the armour they just cut that annoying stuff off flush to get it out of the way. So now, as you so astutely noted, they are trying to make a compliant installation out of a cluster-fk!

It is my job to ensure that everything is first and foremost SAFE for the end users...but at the same time try and apply some kind of standard to the installation as well...neither of which are easy at times!

Thanks Again!


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## nick (Feb 14, 2008)

*paralled paths to earth*

Well Rick , from what you said and looking at it iam not much help and i maybe wrong ? But i see a multi paralled paths for current and voltage if you add ground rods it gets worst to me . i wish i could be there to see what or how so do not listen to me please . If these are cables or cannon plugged connections it might be a bigger issue meaning leak to least point to ground like closest metal grounded object on site one lost ground connection in the stream is bad news . just dont understand how one can combine and then open earth ground between points its not good . Take care Rick be safe sorry we could not help ya


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## RePhase277 (Feb 5, 2008)

Trimix-leccy said:


> Just a thought, it may make it easier to comprehend if you remember that EVERYTHING before the *-S *is refering to the supply authorities side.
> 
> So the tncs means the suppliers side has the n and e combined [*C*] and the installation is seperate [*S*]
> 
> tns means the suppliers side n and e AND the installation n and e are seperate [*S*]....see, told you so! clear as mud!!:laughing:


If the neutral and earth are separate at the supplier side and the consumer side, where is the fault path established? In the States, the utility earths the neutral of the transformer and supplies us with the hot and neutral conductors only. At our service equipment, we bond the neutral to the metal cabinet, and each branch circuit gets a neutral and a separate safety "ground" wire also tied to the neutral. After the service, we never tie the safety ground and neutral again.

In what you describe as a TNS, there is no tie at all, on supply or consumer, so where does fault current go to complete the circuit?


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## TheRick (Apr 13, 2008)

InPhase277 said:


> If the neutral and earth are separate at the supplier side and the consumer side, where is the fault path established? In the States, the utility earths the neutral of the transformer and supplies us with the hot and neutral conductors only. At our service equipment, we bond the neutral to the metal cabinet, and each branch circuit gets a neutral and a separate safety "ground" wire also tied to the neutral. After the service, we never tie the safety ground and neutral again.
> 
> In what you describe as a TNS, there is no tie at all, on supply or consumer, so where does fault current go to complete the circuit?


In the TN-S system there is a bond betweeen the neutral and protective (aka ground/earth) conductors at the source, from there they are seperate (where the S comes from). So they are bonded, but are delivered on seperate conductors to the premises. In the TN-C-S you are provided with on combined condcutor that is the neutral and the protective in one. You then bond this conductor to basically everything you would bond your grounding electrode system to in the states except for that grounding electrode (not required), there is however much testing that is required to prove that a very low impedance path is provided to facilitate the operation of the overcurrent protection. From that bonding point you then have a protective conductor (equipment ground) to bring to all your devices.

Hope that helps...I am still learning myself...as fast as I can!:blink:


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## Trimix-leccy (Dec 4, 2007)

InPhase277 said:


> If the neutral and earth are separate at the supplier side and the consumer side, where is the fault path established? In the States, the utility earths the neutral of the transformer and supplies us with the hot and neutral conductors only. At our service equipment, we bond the neutral to the metal cabinet, and each branch circuit gets a neutral and a separate safety "ground" wire also tied to the neutral. After the service, we never tie the safety ground and neutral again.
> 
> In what you describe as a TNS, there is no tie at all, on supply or consumer, so where does fault current go to complete the circuit?



Ah! You read what I wrote and not what I THOUGHT i had written:shifty:
It was late, I was tired etc etc etc! sorry

Supply authority supplies an earth [seperate] with a TNS service [originates from tranny] and an earth derived locally from the neutral within their cutout. Only variations are with TT where you supply tour own Earth via a rod and protect all installation with an RCD.

To quote the US Sitcom "Soap"........._Confused??...you will be _


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## sparkie (Apr 2, 2008)

last time I checked TNC in the uk required a licence-hence you don't normally see it in factories etc.
my advice would be look at a uk substation and you will find there are massive earthing grids buried in ground. wooden overhead lines the poles are grounded at intervals. supply to house split concentric to TNCS.

If your working on an elliot porta cabin type building, then supply earth and rcd board with earth stake to ground-acceptable


Finally I asked about TNCS overhead supply to remote farm building and the regs and electricity board will allow extra earth stake on TNCS and rcd in these situations great idea.

What you need to consider is the reliability of the earth as well.


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## RePhase277 (Feb 5, 2008)

Trimix-leccy said:


> Ah! You read what I wrote and not what I THOUGHT i had written:shifty:
> It was late, I was tired etc etc etc! sorry
> 
> Supply authority supplies an earth [seperate] with a TNS service [originates from tranny] and an earth derived locally from the neutral within their cutout. Only variations are with TT where you supply tour own Earth via a rod and protect all installation with an RCD.
> ...


I see. A pic posted on the other thread help clear my confusion. I have modified it to show the typical U.S. install. The principle is the same for single and 3-phase.


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