# Grounding (earthing) U.S. vs. U.K.



## RePhase277

I am curious as to the differences in the manner of service and branch circuit grounding between the two countries. I'll give some background for the U.S. system and you guys can explain how you are required to do it.

Here, the utility grounds the neutral on the secondary side of the transformer. The service to a premises consists only of the hot conductors and the neutral. At the first disconnecting device the electrician is required by code to connect the neutral to the earth again, through various means, including water pipes and rods driven into the ground.

Now here we have to make a trade-off, because this setup means that some small portion of the neutral current will take the parallel path through the earth from the electrician's ground to the utility's ground. Alot of folks are uncomfortable with the idea of neutral current flowing through the earth, albeit small.

Now the idea is that we ground our neutral so that a lightning strike has the shortest possible path back to the earth. So there is the trade. On the one hand we don't like neutral current flowing in the earth. We could prevent this by eliminating the ground at our service and running a grounding conductor to the utility's neutral at the transformer.

On the other hand, this would increase the distance a lightning strike would have to travel before it finally reaches the earth (at the transformer). Most likely it will find an even shorter path somewhere in the building, such as a water pipe or structural member.

Guess I don't mind a little neutral current in th earth after all... How is it done in the U.K.?

InPhase277


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## cornishsparks

Yes our system is similar, normally the transformer is earthed to ground (centre) our supply cable is normally two core (concentric) for single phase and four core for three phase.
When the service enters the building .service fuse normally called cut out
the neutral and earth are linked.then seperate protective conductor and neutral then feed the instalation. the neutral and earth are never linked after the service fuse,except the icoming water pipe and gas main are earthed. this is called a TNCS SYSTEM.
TNS system is normally an underground service where the earthing connection is made to the incoming cable sheath at the cut out a seperate earth supplied or by the earthed sheath, some areas install three core cableto the cutout
TT sysem is where the POCO will not supply an earth and the installer must provide an earth via a main switch RCD (GFCI) breaker and an earthing conductor is connected to a driven earth (ground rod) In all cases at least one point of the source of supply is directly connected to earth (ie neutral of a single phase transformer or the star point of a three phase) The neutral and earth are never rejoined in the installation after the supply fuse.


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## frank

In Phase.

If you were to bond all metalwork in the dwelling - water/gas/AC/central heating/pools/baths/sinks/girder frameworks etc, and then bring all these seperate bondings to a common location and then have them connect to neutral (as is the case in the UK) would that give you sufficient confidence against a lightning strike. The prospect of disparate currents passing from house to house seems more of a danger than the possibility of a lightning strike to a building which has contact with, together with the water/gas/oil services in- the ground. Interesting topic.

Frank


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## RePhase277

frank said:


> In Phase.
> 
> If you were to bond all metalwork in the dwelling - water/gas/AC/central heating/pools/baths/sinks/girder frameworks etc, and then bring all these seperate bondings to a common location and then have them connect to neutral (as is the case in the UK) would that give you sufficient confidence against a lightning strike. The prospect of disparate currents passing from house to house seems more of a danger than the possibility of a lightning strike to a building which has contact with, together with the water/gas/oil services in- the ground. Interesting topic.
> 
> Frank


We bond that way here anyhow. It's just that in most residential construction, the water supply mains are increasingly becoming plastic as is the gas mains, the building itself is wood, so the path for lightning current is through the electrical system back to the neutral, then to earth.

Our split single phase system, if properly balanced, creates very little neutral current. I don't know how much actually circulates in the earth, but it is small compared to the 10,000 amps of a lightning stroke!

The further the lightning has to travel, the more chance it has to do damage by arc offs. So we ground at the service entrance (cut out?).

I've heard two different statements about how your system is grounded. Cornishsparks said you do it similar to us, with a ground at the utility xfrmr, and again at the cut out. Another post I've read mentioned that your system is grounded only at the utility, and a separate conductor is provided from there along with the hot and neutral.

InPhase277


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## Trimix-leccy

I've heard two different statements about how your system is grounded. Cornishsparks said you do it similar to us, with a ground at the utility xfrmr, and again at the cut out. Another post I've read mentioned that your system is grounded only at the utility, and a separate conductor is provided from there along with the hot and neutral.

InPhase277[/quote]


Just to confuse things,we do both 

Most older properties are TNS ie there are 3 conductors brought into the property, Live, Neutral, Earth
Newer properties are usually TNC-S, Live and neutral brought into property and Neutral split to provid a seperate earth connection. All this is sealed within the cut-out and we are just presented with the earth point. The rest being down to the POCO.

In my area [coastal ] the POCO have changed a lot of the services to TNC-S because of network problems.A lot of the old services use something called a 'trifurcating box'. This is a cast iron box which forms a 'T' [splice] onto the cable beneath the pavement. The cables have a lead sheath which is the Earth connection. Continuity is created across the 'box' by screwing a brass gland into the box and sweating/plumbing the lead sheath onto this. Because of the high level of salt in the ground the boxes are rusting and the continuity/ earth is lost so they are bonding Neutral to Earth in each consumers property:thumbup: Does that make it any clearer:no:


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## cornishsparks

Our local service provider (POCO) think we should call them that in the UK
have had problems with their lead sheath mains cables breaking down.
Have has ze loop readings of 450 ohms when i complained they say they can know longer provide cable sheath earthing and you will have to go on TT at your own expense rather than sort the problem out.


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## colin

I was reading the other day that instead of changing to a tt system when the ze is failing. That you can fit an rcd which inturn allows your zs readings to rocket up,but be regarded as safe


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## chrisb271

We used to go to 100 ohm max on earth rod with RCD ( GFCI ) but have known it higher in some places.

People put too much trust in an rcd.
The NIC man always goes on about how great they are,i have reservations about trusting them so much.

They do often fail.

Chris


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## Trimix-leccy

chrisb271 said:


> We used to go to 100 ohm max on earth rod with RCD ( GFCI ) but have known it higher in some places.
> 
> People put too much trust in an rcd.
> The NIC man always goes on about how great they are,i have reservations about trusting them so much.
> 
> They do often fail.
> 
> Chris


Ah, the NIC man. :notworthyue soon to a village near you if I remember correctly?

Got all your paperwork, certs,books,regs,H&S Statement,Calibration certs,complaints procedure,NIC shares,GS38 leads, lockouts,plant and machinery commensurate with your type of work?.....after checking all that he may even look at a couple of jobs

Yep. you guessed correctly. I've got one in 3 weeks time. HeyHo!


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## chrisb271

When i was on the electricity board we used the letters to mean various things,they still exist today,they are -

first letter indicates the type of supply earthing
*T *indicates that one or more points of the supply are directly earthed( usually at the transformer point star )

*I *indicates either that the supply system is not earthed at all,usually with deliberate inserted impedances ( not used in the uk now )

second letter indicates the earthing arrangement in the installation

*T *all exposed conductive metalwork is connected directly to earth.

*N *all exposed conductive metalwork is connected directly to an earthed supply conductor provided by the electricity supply company.

The third and fourth letter indicate the arrangement of the earthed supply conductor system

*S *neutral and earth conductor systems are quite seperate

*C *neutral and earth are combined into a single conductor


hence we get* TT TNS TNCS*


JUST A BIT OF USELESS INFO 


Chris


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## chrisb271

Deep joy ! mines next week,must remember to hide the quick earnerer jobs so he cant look at them :whistling2:

Yes a day totally wasted on tripe ! i've gone moist at the thought 

Chris


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## cornishsparks

Never been able to get an earth rod much below 175 ohms any where in Cornwall especially where there is beach sand near the coast, but the other day i got 78 OHMS on a TT rod i drilled through a concrete slab in the customers garage, most unusual.
Napit have told thier members you can except up tp 2000 Ohms as a reading but ive always thought it was 200.


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## colin

I have never had much luck with earth rods and try to stay clear of this horrible job. The lowest reading I have had was around 58. But I always struggle to get the dam things in!


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## Trimix-leccy

colin said:


> I have never had much luck with earth rods and try to stay clear of this horrible job. The lowest reading I have had was around 58. But I always struggle to get the dam things in!


Best I have had was on the last job, 83. I even bought a proper real Kosher Earth resistance tester as the Genny people wanted to see it tested and how. £58 !!!! well I thought it was cheap. As for knocking it in, we have 2 methods [3 if you count the lump hammer]
1) Kango hammer. Set to hammer but fit the drill [K type steel] adapter. This has a hole in it which fits the earth rod coupler a treat. Pull the trigger and the rest is history

2) managed to break an SDS chisel bit. Turned down the end in the lathe so that it is just less than the diameter of the hex hole in the driving screw. Bit of tube fastened [welded] to the tube as a guide. Fit to rod, pull trigger, lock trigger on and have a brew whilst sitting and watching it drive itself into terra firma


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## frank

Cornish. If you get 2000 earth value resistance on a rod - then best not switch on! 200 is max but I have rarely gotten less than 150. I always ensure for 100 or less even if this means using multiple rods or burying a bath tub.

Frank


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## colin

what the max your allowed on tncs and tns sytems?


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## chrisb271

Trimix-leccy said:


> Best I have had was on the last job, 83.


 
5.32ohm 

Read it and weap boys ! :notworthy:

Mind you we did bung down 9 x 20mm copper bond rods and a full bag of bentonite :whistling2:

And it was on Boston flats where its wet 

Chris


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## chrisb271

When i was on the board we regular used to get 0.85 but it was always with a copper grid the size of Wales and stacked with bentonite 

Chris


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## cornishsparks

We just bury a Massey Furguson in the back yard and take off the tyres to use to hold down the tarpauline that stops the roof from pissing in water.
Makes a good earth rod !
How many of you saw a bit off when it wont go no more, or forget to put the clamp on or feed it through the protection cover,!


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## frank

Colin.

You wouldn't use a rod on any of these systems. Just TT by and large. There are other service situations that you would need to install rods ie weigh bridges etc - but for the most part TT only or special manufacturing situations, Sure Chris can fill in here,

Frank


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## chrisb271

Ahh i see what your doing wrong straight awayCornish ,if you bury an old fergie in your back garden then you will get crap results.you should use a John Deer as the old farmers say " Nothing runs like a deer" 

Chris


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## Trimix-leccy

chrisb271 said:


> 5.32ohm .....note to self...'check meter calibration'
> 
> Read it and weap boys ! :notworthy:
> 
> Mind you we did bung down 9 x 20mm copper bond rods and a full bag of bentonite :whistling2:
> 
> And it was on Boston flats where its wet
> 
> Chris


Ah! Bentonite. I have a customer which puts it into 'Mats' to line waste pits etc. Also used in babies nappies, grounds maintenance on sports pitches and I am lead to believe as a constituent of the thickener in mister Donalds milk shakes [allegedly, for reasons of litigation etc]...enjoy lunch


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## chrisb271

colin said:


> what the max your allowed on tncs and tns sytems?


 
As Frank says Colin we don't use a rod on TNCS or TNS,thats done externaly.

The figures they aim for Ze ( external impedance is 0.80 for TNS and 0.35 for TNCS allthough i've had figures like 0.90 and 0.42 respectively )

On TNCS (PME)the neutral is earthed at most poles

TNS is earthed at origin.

Filling stations and garages all should be put on TT NOT PME.

Chris


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## chrisb271

chrisb271 said:


> 5.32ohm .......Note to self,Just remembered that calibration was done prior to test.
> 
> Read it and weap boys ! :notworthy:
> 
> Mind you we did bung down 9 x 20mm copper bond rods and a full bag of bentonite :whistling2:
> 
> And it was on Boston flats where its wet
> 
> Chris


 
The joys of a bentonite lifestyle !

So thats why i have a job removing the stains from the toilet bowl after a visit to Mr Donalds 

Chris


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## Trimix-leccy

chrisb271 said:


> The joys of a bentonite lifestyle !
> 
> So thats why i have a job removing the stains from the toilet bowl after a visit to Mr Donalds
> 
> Chris


Use their 'Pokey Pola or Rola Cola'...well you can't drink it.

At least Kentucky have the good manners to provide thier 'fried rat' in a bucket so you have something to vomit in


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## chrisb271

They give you a special white sick bag at donald mc ronalds and a free tissue to wipe the sick off your shirt :blink:


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## cornishsparks

Chris, All the farmers round here drine 40K air conditioned tractors paid for by us from thier set aside and european grant funding. Get a digger, bury them in a field, claim on the insurance the dig them up again twelve months later.


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## septiclecky

chrisb271 said:


> When i was on the electricity board we used the letters to mean various things,they still exist today,they are -
> 
> first letter indicates the type of supply earthing
> *T *indicates that one or more points of the supply are directly earthed( usually at the transformer point star )
> 
> *I *indicates either that the supply system is not earthed at all,usually with deliberate inserted impedances ( not used in the uk now )
> 
> second letter indicates the earthing arrangement in the installation
> 
> *T *all exposed conductive metalwork is connected directly to earth.
> 
> *N *all exposed conductive metalwork is connected directly to an earthed supply conductor provided by the electricity supply company.
> 
> The third and fourth letter indicate the arrangement of the earthed supply conductor system
> 
> *S *neutral and earth conductor systems are quite seperate
> 
> *C *neutral and earth are combined into a single conductor
> 
> 
> hence we get* TT TNS TNCS*
> 
> 
> JUST A BIT OF USELESS INFO
> 
> 
> Chris


 
And to totally confuse things the *T* actually stands for *Terra* from the French for *Earth*:thumbsup:


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