Earth Rod Location

daimack · Apr 14, 2012

Gents,

Please can I seek the opinion of those experienced in positioning earthing rods (this is my first time!!!)

I am about to start a full rewire on an old mid terraced house, which is currently unoccupied. The existing electrics are ancient, so everything has to be renewed.

Its a TT system, but there doesn't appear to be an earthing rod; I suspect it used to rely upon the water main as an earth (although at some stage that has been upgraded to plastic!)

The meter is just inside the front door, and it a "straight onto the street" house so there's no front garden to put an earth rod in. The downstairs floors are concrete. As I will be doing a full rewire all the floorboards will be coming up, so from a practical point of view it would be easy to run the main earthing conductor through to the back garden (its not a large house) where there is ample scope for an earthing rod.

It looks to me as if my options are;

To put an earthing rod at the front, although this would technically be on the local authorities pavement by an inch or so, so would I need to ask permission from them? A couple of other houses on the street appear to have done this already, although the down side -apart from the council agreement- seems to be the relative difficulty of driving the rod through the pavement (I don't know what rubble / services / foundations might be under there) and that the rod may be more vulnerable to damage from pedestrians / buggies etc over time, although it could be mechanically protected, or

To run the conductor through the house and put the rod in the back garden, where it would be easy to drive and less vulnerable to damage. The only down side I can see here is that the conductor would be longer and therefore have a higher impedance, but we are only talking of a house that's about 35-40'front to back in total.

I'm swaying towards the back garden - does anyone have any views as to what would be the best option?

Thanks in advance,

Dave

malcolmsanford · Apr 14, 2012

Well chances are Dave that if you get a Rod under 100ohms in value say 75 ohms 40ft of cable is not going to do too much damage to that, might get it up to 75.08 ohms .................................. so don't fret too much.

Really no brainer out the back mate

daimack · Apr 14, 2012

Thanks mate, thats kinda what I was hoping people would say! I figured the extra impedance would be negligible in the greater scheme of things, but in honesty I was thrown a bit by the fact that a couple of the neighbours did have rods at the front and was starting to wonder if I was missing something. I guess perhaps if their earths were being updated without a full rewire then maybe that was the easier option at the time to avoid lifting all the boards. Anyway, thanks for the reply!

Engineer54 · Apr 14, 2012

First off, check your local DNO if your distributed supply line has been PME'd or not!!

As Malcolm states, it's a no brainer to locate your Rod(s) in the back garden, try and keep a good 1 or 2 metres away from the external house wall, which is where you will hit all the old building rubble. Don't what ever you do, make use of those 3/8'' twigs they have the cheek to call earth rod. use 5/8'' extendable rods, and use a minimum of 2 coupled rods for depth and stability!!

Check out the other similar threads at the bottom of this page, and other threads relating to TT systems, to get a broader outlook on your TT installation....

malcolmsanford · Apr 14, 2012

Yes Dave quite a few places round me are the same. My mate has his in his porch next to the intake. In the good old days when earthing was an optional extra, you stuck the rod in and relied on the mains service to back you up.

So in many cases the rod was literally throw it in the air and where it lands that will do.

With RCD protection now, your more likely want a stable earth value. So site it away from a wall, about a metre to clear any old rubble that was left in the building and try to get deep.

There are countless arguments on here about the values, personally I prefer depth rather than too much about value, If I can get a couple of rods in the great, and if the value of those rods are exceptionally a bit of Bentotite helps

Engineer54 · Apr 14, 2012

malcolmsanford said:
if the value of those rods are exceptionally a bit of Bentotite helps

Bit late for Bentoite, after the rods are in the ground!! lol!!!

malcolmsanford · Apr 14, 2012

Engineer54 said:
Bit late for Bentoite, after the rods are in the ground!! lol!!!

True always good if next door had a rod to nip in and see what values they had before starting, but I have know guys to improvise while fitting rods

daimack · Apr 14, 2012

Thanks for the advice gents, much appreciated!

Just out of interest (assuming I have uploaded the picture right!) attached is a photo I took of the "consumer unit" at the house. I suspect it may not comply with the current edition of BS7671 - or the one before! (the meter is just out of shot on the left).

malcolmsanford · Apr 14, 2012

Not so much a consumer unit but a varied array of switch fuses by the looks of things

As this is a TT I guess there must be some sort of upfront RCD, most likely looking at those it's an ELCB......................please tell me there is one !!!!

No I think you may have to recommend fitting a new CU to replace that lot

Engineer54 · Apr 14, 2012

daimack said:
Thanks for the advice gents, much appreciated!

Just out of interest (assuming I have uploaded the picture right!) attached is a photo I took of the "consumer unit" at the house. I suspect it may not comply with the current edition of BS7671 - or the one before! (the meter is just out of shot on the left).

I suspect this installation hasn't been touched since sometime in the 50's, i doubt very much, that there is any form of RCD/ELCB up front protection...lol!!!

telectrix · Apr 14, 2012

i see the phantom painter has been. more paint on the electrical gear than on the wall.

WPD Lad · Apr 14, 2012

As previously stated speak to the DNO about the possibility of getting a PME (TNC-S), will save you a load of aggro and the customer will get a nice shiny new cutout to match the rest of the installation!

ipf · Apr 14, 2012

telectrix said:
i see the phantom painter has been. more paint on the electrical gear than on the wall.

Yea, looks like the cables have been pasted to the ceiling before being papered over ,too. Is it in some kind of lean-to or small extension ?

daimack · Apr 14, 2012

Thanks again all, and will definitely take the advice of confirming with the DNO first. Obviously the whole lot will be changed and maybe there will be a place for the old gear in a museum somewhere!

All your help is much appreciated,

Dave

daimack · Apr 14, 2012

ipf said:
Yea, looks like the cables have been pasted to the ceiling before being papered over ,too. Is it in some kind of lean-to or small extension ?

Sadly not mate, this is how the whole house was wired, hence the need for a full rewire. You are right though, in most places the wires have just been run down the walls and then papered over. I suppose (and I'm really trying to look for the silver lining here), at least by doing that they were less likely to drill into a concealed cable! And as telectrix says there's paint everywhere.

Earth Rod Location

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