earthing

[--tom]

Q1 can one earth to both the fusehead and to an earth rod. in what circumstances would this arrangement ever be required?
Q2 what is the most usual earthing arrangement in, say, a new build smi-detached?

 

[securespark]

Are you rural?

In towns, the most common form of supply is underground with earth supplied via the cable TN-S or TN-C-S if the earth is bonded to the Neutral. If TN-S, the Regional Electricity Company (REC) will sweat an earth onto the sheath or if modern cable, the earth is contained within the cable.

Out of town, overhead supplies (TT) that need an earth rod are common, but some overhead supplies have an earth too.

(This has no nomenclature - could it be TT-S??)

If you have an earth terminal supplied by the REC, then you should not need a rod, and if you don't have an earth with your supply then you definately need an earth rod.

Perhaps the best course of action would be to get a test done on the integrity of the supply earth to see if it is up to the job.

 

[Big_Spark]

Sounds to me like he's at college and wants us to answer his homework questions for him..cheeky scamp

However, in the spirit of helpfulness,

Earth Rod at an installation may be used in Two instances as described.

• 
  1 . A TT type Domestic, Commercial, Industrial Supply
  
  2 . A Temporary Installation supplying power to a construction site which is always designated as TT by the Supply authority.

Regarding Question two, this is purely decided by location. In Metropolitan areas and similar large conurbations, the usual method with be either TN-C-S (PME) or TN-S. However this picture can get a little muddled in more rural areas where overhead power transmission is common, in this case the supply will likely be TT, however some TT lines also incorporate a seperate Earth conductor which is linked back to the local transformer which in turn is connected to earth via either a local Earth rod/plate, or linked by another earth cable back to the main localisied substation where it will pick up the earth via the concentric cable feeding the unit.

 

[securespark]

Just Out of interest Jim, I mentioned "TT-S" earlier.

What do you call an overhead supply with no earth rod where the earth is bonded to the neutral where it enters the property??

TT-N-C-S??????


Seriously, I found this today in a rural cottage 400 y.o.

 

[plugwash]

sounds like a PME: earth in property joined to supply neutral

 

[ban-all-sheds]

TN-C-S, what else?

TT doesn't mean "overhead", it's just that most overhead supplies are (were) TT, and most (all?) TT supplies are overhead.

I imagine that what you're seeing when there is an earth rod and a connection to the suppliers neutral is not some weird hybrid of TT and something else, it's one of the multiple earth connections installed by the supplier, which gives TN-C-S its other name of PME.

 

[ban-all-sheds]

sounds like a PME: earth in property joined to supply neutral

Doh! - too slow typing again!!!!

 

[plugwash]

i think most TT supplies in permanent household installs are overhead

TT was a way to save money on cableing before someone came up with the not very bright idea of PME

with the regs not installing TN-S distribution anymore (to save money i presume) TT supplies are i belive common in the places where PME is banned (either by regs or by guidence notes for situations the regs don't yet cover)

outdoor events
construction sites
caravan parks
marinas
petrol stations

 

[securespark]

Oh, it most definately is PME as the earth is bonded to the neutral at the cutout, but it's the first time ever I've seen this done with an overhead supply.

The only other time I've seen a supply intake altered to PME (as opposed to a PME installation from the off) was in Bristol where SWEB (then) altered a TN-S intake to PME.

 

[Big_Spark]

It's not PME, as this is TNC-S, what this is is TN-C, (Typo by me..there should be no C on the end, just TN..apologies)and is often used in newer or rewired overhead systems.

My Supply is an adapted TT system that has no official designation. The Earth Conductor linking the Tx to Earth is actually the lightning conductor which has multiple groundings, namely a rod every 6 poles.

 

[ban-all-sheds]

It's not PME, as this is TNC-S, what this is is TN-C, and is often used in newer or rewired overhead systems.

Funny - I could have sworn that TN-C meant that the combined neutral and protective conductor arrangement was carried on throughout the installation, not ending where the supply enters. i.e. TN-C-S, but with the Separation of the neutral and protective removed. And as such, pretty unusual in domestic situations, earthed concentric cables, no point to RCDs etc etc.

No?

My Supply is an adapted TT system that has no official designation. The Earth Conductor linking the Tx to Earth is actually the lightning conductor which has multiple groundings, namely a rod every 6 poles.

Also wrong - there are not 6 poles to a rod, a rod and a pole (and a perch) are all the same - 5.5 yards, or 1/8 of a furlong.

 

[Big_Spark]

Ban, ...typo on my part..should have been TN with no C on the end..so used to typing the bl**dy thing though!!

However, in reality the system is a mix of TN-C and TN, the supply cable is most certainly TN-C, however the installation is TN....


Regarding your last comment...I think you need a Doctor fella!!

 

[ban-all-sheds]

So you've got combined neutral and earth on the supply where it enters your house, and then, presumably, separate neutral and earth throughout your house?

 

[Big_Spark]

So you've got combined neutral and earth on the supply where it enters your house, and then, presumably, separate neutral and earth throughout your house?

Yep, all it is is an adapted TT supply where they ground the Neutral in multiple locations with the lightning conductor earth rods and at the substations. However in your home they install a PME head and split them again for the a standard domestic installation with seperate conductors...that is how it was described to me by a friend who is a 24/7 Overhead Engineer anyway

 

[breezer]

a question FWL_Engineer if i may, your mate who is an overhead lineman,
would you ask him what it was like the first time he went in one of those little baskets they hang on over head lines, i used to watch them at my ex sisterin laws place, i didnt believe her untill one day i saw 3 coming down the same line