no earth

[Stroppy]

Two rods screwed together, so 8 feet.

 

[Geordie Spark]

how deep have you gone?

All the way to my bow locks.

 

[Engineer54]

Two rods screwed together, so 8 feet.

They weren't 3/8'' rods then, if you were able to couple them together!! The 3/8'' things, are the twigs that you can't couple!! lol!!

Go back and test that new rod installation in 6 months time, you'll see almost certainly see an improvement on the present 44 ohms, ..and it will continue to improve for the next 18 months or so, as the soil slowly compacts tightly around the rods....

 

[ackbarthestar]

Exactly, I told you that 'twig's were the way to go.

Wack a 1.2m 'twig' in and the the Ra will decrease because of the contact resistance around the electrode.

Better still, back fill with conducting cement and you've increased the contact resistance immediately.

As an aside, it only works when the soil conditions are right and Hong Kong, Gibraltar and most of Norway plus the Himalayas and a couple of places just outside our local pub are not the best places for any 'twig'

 

[Engineer54]

Exactly, I told you that 'twig's were the way to go.

Wack a 1.2m 'twig' in and the the Ra will decrease because of the contact resistance around the electrode.

Better still, back fill with conducting cement and you've increased the contact resistance immediately.

As an aside, it only works when the soil conditions are right and Hong Kong, Gibraltar and most of Norway plus the Himalayas and a couple of places just outside our local pub are not the best places for any 'twig'

You can sum that up very easily, where twigs are concerned No-where will twigs be any good!!

I wouldn't say Hong Kong is a particularly bad area for creating a TT system, far from it in fact, depends where your trying to create the system. Remember Hong Kong isn't just the Island(s), it also incorporates a section of the mainland too!! lol!!

The earthing on both the Stations and the tunnel overhead rail system, as a whole, was impeccable on the MTR (Mass Transit Railway). I know because i was responsible for large sections of it, along with various much needed CP systems to suit!! ..lol!!

 

[Stroppy]

Oops my mistake, they are 5/8" not 3/8". These mediaeval measurements confuse me! 10 or 15mm make more sense to me. (see: What we SHOULD have been taught in our senior year of high school - The Oatmeal )

I will try to remember to retest in a few months time, as hopefully the soil around the top rod will have settled a bit. At the moment with all the movement from driving it in it is flapping like a dick in a shirtsleeve.

As an aside, it only works when the soil conditions are right and ...a couple of places just outside our local pub are not the best places for any 'twig'

Oh I don't know, all the wee would keep the soil nice and moist! Although may corrode the rod quite quickly.

 

[ackbarthestar]

I will concede that you are referring to a fully integrated system over several miles - hardly 'twig' territory.

The basic two up two down domestic installation with a 'twig' would suffice, IMO, as long as you get a reasonable Ra of less than about 50 Ohms and as you say this value is likely to decrease as the electrode beds in.

In any case, unless you can get the value of Ra below 1 Ohm you'll need supplementary protection Earth fault protection from RCDs

 

[ackbarthestar]

Oops my mistake, they are 5/8" not 3/8". These mediaeval measurements confuse me! 10 or 15mm make more sense to me. (see: What we SHOULD have been taught in our senior year of high school - The Oatmeal )

I will try to remember to retest in a few months time, as hopefully the soil around the top rod will have settled a bit. At the moment with all the movement from driving it in it is flapping like a dick in a shirtsleeve.


Oh I don't know, all the wee would keep the soil nice and moist! Although may corrode the rod quite quickly.

Backfilled with rubble with an overlay of concrete and tarmac ? You'd probably need a 10m RSJ pile driven into the ground

 

[Engineer54]

I will concede that you are referring to a fully integrated system over several miles - hardly 'twig' territory.

The basic two up two down domestic installation with a 'twig' would suffice, IMO, as long as you get a reasonable Ra of less than about 50 Ohms and as you say this value is likely to decrease as the electrode beds in.

In any case, unless you can get the value of Ra below 1 Ohm you'll need supplementary protection Earth fault protection from RCDs

Well for a start i wasn't referring to twigs in my assessment of Hong Kong, just that it isn't a particularly ALL bad area to create TT systems. I don't think i've ever seen a 2 up, 2 down residence in Hong Kong, they are all high/medium rise apartment blocks, or massive residence's of the very rich!! lol!!

Nope, ...it wouldn't, for a kick off there is no-way that a twig will offer any form of a stable TT system to an installation.

Twig electrodes are no good to man or beast, they are little more than the size and thickness of test spikes used for testing Real electrode rods... lol!! I've actually never seen one either, and certainly not in any of the countries i've worked in. Say's a lot for the UK, when you think about it!! lol

 

[Engineer54]

Oops my mistake, they are 5/8" not 3/8".

I will try to remember to retest in a few months time, as hopefully the soil around the top rod will have settled a bit. At the moment with all the movement from driving it in it is flapping like a dick in a shirtsleeve.

That's why most electricians that do a lot of TT installations use a SDS with either a shop made or home made driving head, to drive rods into the ground, ....and in a fraction of the time it probably took you. ...lol! It also considerably reduces the flapping about of the rod during installation, that you get when using a club hammer or the like!!

 

[Stroppy]

I was wondering about using my hammer drill while hammering it in, but couldn't think of anything suitable to use as a driver. If I have to do another one I'll get my thinking cap on and make something.

Just found a good home-made solution. I like the rubber hose sleeve to stop it slipping off! http://www.n4lcd.com/groundrod/

 

[Engineer54]

I was wondering about using my hammer drill while hammering it in, but couldn't think of anything suitable to use as a driver. If I have to do another one I'll get my thinking cap on and make something.

Just found a good home-made solution. I like the rubber hose sleeve to stop it slipping off! Easy Ground Rod Driver

Better still, weld a suitable sized socket (to fit the driving head bolt) to that chopped off SDS chisel. lol!!
Remember they don't seem to sell 8' (2.4m) rods that much in the UK anymore, they tend to be 1.2m extendable from what i can gather. So using your suggestion, will damage the rods threads, maybe to the point of making it impossible to couple another rod on to it!! Use a coupling screwed onto the rod with a driving bolt screwed into the other end of the coupler, and use my suggestion above to drive the rod into the ground!! lol!!

I have two such home made head drivers as described above for both 5/8'' and 3/4'' rods. Had them for a good 25 years now too!! lol!!

 

[Stroppy]

Ah that's a great idea with the socket and bolt. I have in my toolbox an already-damaged coupler which I used to avoid damaging the rod threads. Sometimes I love this forum!

 

[GLENNSPARK]

Ah that's a great idea with the socket and bolt. I have in my toolbox an already-damaged coupler which I used to avoid damaging the rod threads. Sometimes I love this forum!

but never forget....dig a pit first where you intend to site rods....to ensure you wont be intercepting any services with the rods.....

 

[Engineer54]

I hope he's installed a decent earth inspection pit over the rod location he's just installed too!! ...lol!!

 

[Stroppy]

I've put a cardboard box over it, that should do!

 

[Guitarist]

I've put a cardboard box over it, that should do!

Properly varnished I hope...

 

[Engineer54]

I've put a cardboard box over it, that should do!

Does that mean you didn't install an earth pit then?? If so what have you used to protect the cable connection to the rod??

 

[Geordie Spark]

Does that mean you didn't install an earth pit then?? If so what have you used to protect the cable connection to the rod??

I saw one with half a bucket of cement tipped over it once.

There it was, in a corner of a backyard, a pile of hardened cement with a length of 6mm green/yellow protruding from it & running through a hole in the back wall of the house.

 

[Engineer54]

I wonder what they thought they were going to achieve by doing that?? lol!! The chemicals in the cement will probably be doing more harm than good to the connection!! lol!!

 

[Stroppy]

Does that mean you didn't install an earth pit then?? If so what have you used to protect the cable connection to the rod??

No I didn't. The rod has a green box on it, and the cable is protected from damage by going through a length of flexible conduit into the house.

 

[Engineer54]

No I didn't. The rod has a green box on it, and the cable is protected from damage by going through a length of flexible conduit into the house.

What do you mean by a green box?? It's the actual cable to rod connection that needs ''long time'' protection.

 

[GLENNSPARK]

What do you mean by a green box?? It's the actual cable to rod connection that needs ''long time'' protection.

what i cant understand as well is what a bit of copex is supposed to do against Mr. Fothergills spade?...

 

[stuartcourt]

what i cant understand as well is what a bit of copex is supposed to do against Mr. Fothergills spade?...

I think we should open up the depth in garden thread again, I never felt we drew a line under it anyway

 

[Geordie Spark]

I wonder what they thought they were going to achieve by doing that?? lol!! The chemicals in the cement will probably be doing more harm than good to the connection!! lol!!

I agree.

The job was done by a couple of blokes in a white Transit van with NICEIC plastered all over it.

 

[Stroppy]

What do you mean by a green box?? It's the actual cable to rod connection that needs ''long time'' protection.

One of these green boxes that say "safety electrical connection" on. Bearing in mind the distance from the rod to the wall is less than 30cm the probability of damage is minimal.

 

[Engineer54]

One of these green boxes that say "safety electrical connection" on. Bearing in mind the distance from the rod to the wall is less than 30cm the probability of damage is minimal.

You'll be lucky if you get 2 to 4 years from that load of crap!! They should ban those bloody things, they stand absolutely no chance of lasting the lifetime of the TT installation!! Which is minimum of 30 years, but in reality much longer... Do yourself a favour and throw that thing away and get a proven propriety flush to ground, concrete or heavy duty plastic earth pit!!

So you drove your rod in the worst area possible on a domestic, straight into all that old builders rubble, ...that was clever!! lol!! If you had gone a metre or so, away from the house walls, you would have probably got a better Ra value too...

 

[DPG]

Don't sit on the fence Eng, do you think it's a good job or not?? Daz

 

[telectrix]

surely that green box doesn't comply with current regs. it should be green/yellow, with neither colour taking over 70% of the surface.

 

[Stroppy]

It is in the same place as the old rod, and as my house was built in 1826 there is no rubble - it is thick clay soil which is giving me a reading of 44 ohms which should get better over time. If the new rod had given me a rubbish reading or encountered rubble (not likely as the original one didn't) then I would have tried further away, but it didn't so it would be totally pointless to go half way down the garden for no reason. When (eventually) I repave the path it will be treated to a proper concrete pit.

 

[Engineer54]

It is in the same place as the old rod, and as my house was built in 1826 there is no rubble - it is thick clay soil which is giving me a reading of 44 ohms which should get better over time. If the new rod had given me a rubbish reading or encountered rubble (not likely as the original one didn't) then I would have tried further away, but it didn't so it would be totally pointless to go half way down the garden for no reason. When (eventually) I repave the path it will be treated to a proper concrete pit.

What are you saying here, that house builders were cleaner in those days?? lol!! In thick top clay with a two coupled together 5/8'' rods, i'd be hoping and looking for an Ra of around 15 ohm as an initial value...
I'd hardly call a metre or so, half way down the garden, unless you only have a small yard out back!! lol!!

 

[DaveyD]

You'll be lucky if you get 2 to 4 years from that load of crap!! They should ban those bloody things, they stand absolutely no chance of lasting the lifetime of the TT installation!! Which is minimum of 30 years, but in reality much longer... Do yourself a favour and throw that thing away and get a proven propriety flush to ground, concrete or heavy duty plastic earth pit!!

So you drove your rod in the worst area possible on a domestic, straight into all that old builders rubble, ...that was clever!! lol!! If you had gone a metre or so, away from the house walls, you would have probably got a better Ra value too...

LOL, I could hear E54's buttocks clench when I read 30cm from wall and plastic box. Your moments were numbered

 

[Stroppy]

Clean builders or not, the point is that the old rod was not in rubble, so the new one in the same place won't be, and if it was I would have felt it scraping on the way down!

Anyway, you can argue all you want, its staying where it is, as is the purpose-made green box, and the 0.75mm green and yellow wire out of some flex that connects it to the consumer unit, and not a separate pointless earthing terminal!!

"lol!!"

 

[GLENNSPARK]

What are you saying here, that house builders were cleaner in those days?? lol!! In thick top clay with a two coupled together 5/8'' rods, i'd be hoping and looking for an Ra of around 15 ohm as an initial value...
I'd hardly call a metre or so, half way down the garden, unless you only have a small yard out back!! lol!!

i think what he is refering to eng is that houses built in the early part of the 19th century tended to have very shallow foundations....if at all.....
many georgian buildings were simply built on bedrock...or soakaways....
still doesn`t mean though that any rods shouldn`t be given the same consideration in regards to siting as any other installation...

 

[Stroppy]

Having been under the floor and seen the foundations when having an extension built, mine seem to be about 2 feet deep. House hasn't caved in in nearly 200 years, so can't be that bad! On a new rod then I would consider the ground conditions.

 

[GLENNSPARK]

Having been under the floor and seen the foundations when having an extension built, mine seem to be about 2 feet deep. House hasn't caved in in nearly 200 years, so can't be that bad! On a new rod then I would consider the ground conditions.

well....careful consideration needs to be paid to where to site rods....
say, a meter away from the building and in a shady area if possible...
dig a pit first to verify that any rods knocked into the ground wont hit any services (cable, pipes etc)...go for 2X 5/8" rods connected together....then get an Ra....
depth is key with TT....

 

[Stroppy]

2x5/8 got me down from 125 to 44. To be honest I was surprised it made such a big difference. I knew I was out of the way of services as (a) there was a rod there already, and anyway I know where all the services go.

Now I've peeled back some of the plastic off my incoming cable and wrapped a wire round the armouring my Ze is even better!

 

[GLENNSPARK]

2x5/8 got me down from 125 to 44. To be honest I was surprised it made such a big difference. I knew I was out of the way of services as (a) there was a rod there already, and anyway I know where all the services go.

Now I've peeled back some of the plastic off my incoming cable and wrapped a wire round the armouring my Ze is even better!

get a third rod connected onto the others and carry on banging it in....whatch that Ra come down....plus it will maintain this stability as well...
happy days strops.
glenn.

 

[Stroppy]

Two's enough for me. Unless I end up making an sds rod driver, then I'll have to test it out!

 

[GLENNSPARK]

Two's enough for me. Unless I end up making an sds rod driver, then I'll have to test it out!

well then do so....
a little weekend project for you....
the depth of those rods are whats going to dictate how much the Ra rises n falls under different weather conditions.....
dont forget that as you get more than about a foot or so below the ground the soil conditions are likely to remain moist throughout the year....as long as their not on a slope of course...or a soft sand/shingle...
thats the idea with going deep with rods....to get below all the dry stuff on the surface.....

 

[Stroppy]

Bog-all hope of the ground drying out these days!

 

[GLENNSPARK]

Bog-all hope of the ground drying out these days!

you dont take the risk though strops.....
a properly sited, well installed TT system would not be unduely affected either way....
we always take the worst case scenareo strops when dealing with electrical installations.....

 

[Stroppy]

I know we should aim for the lowest possible Ra, but how far would you go before being satisfied with a reasonable result? 4 rods, 8? Dig up the entire garden and bury tape and mesh? My 44 is considerably better than the BGB's max of <200. Is there a 'law of diminishing returns' where you could drive stakes to the centre of the earth and still not get much better? Depends on the ground, I suppose - if you hit a spring you might get better.

Bearing in mind with my service bonding connected I am getting 0.45 I'm satisfied I have a good EFL path.

 

[SteveEmartin]

You are permitted to have a Ze for a TT supply up to 200 ohms - Above 200 ohms it may become unstable..

 

[GLENNSPARK]

You are permitted to have a Ze for a TT supply up to 200 ohms - Above 200 ohms it may become unstable..

but you wouldn`t though....would you...lol

 

[Engineer54]

but you wouldn`t though....would you...lol

Oh yes he would, cause the BGB told him so!! lol!!

 

[Engineer54]

you dont take the risk though strops.....
a properly sited, well installed TT system would not be unduely affected either way....
we always take the worst case scenareo strops when dealing with electrical installations.....

Don't waste any more breath on the matter, he obviously knows far more than us!! ..lol!!

 

[Stroppy]

You are permitted to have a Ze for a TT supply up to 200 ohms - Above 200 ohms it may become unstable..
but you wouldn`t though....would you...lol
Oh yes he would, cause the BGB told him so!! lol!!

So considering my Ra was 125 in the first place I should have left it then, but I didn't!
Anyway I'm not bothering to waste any any more time discussing the subject (I see no-one could be bothered to answer my questions), as it is descending into taking the ---- and ignoring genuine discussion, as usual.

 

[Engineer54]

Bearing in mind with my service bonding connected I am getting 0.45 I'm satisfied I have a good EFL path.

Have i missed something along the way??? Why are you installing a TT system if you have a Ze at the service cut-out of 0.45??

And no-ones taking the ----, you asked for advise got it, and then you start pulling it apart to suit yourself!!

 

[Stroppy]

Yes you have missed something. It is an existing TT system of which I was upgrading the rod as it was giving 125 ohms, which technically satisfies the BGB, but it reality is a bit rubbish. The 0.45 is the resistance of my bonded pipework (underground gas and water pipes) when tested without the earth stake (new or old) connected, not the service head. As I know we shouldn't rely on bonding for our earth path I set about replacing the rod, which got it down to 44.

I was joking about peeling back the plastic off my incoming cable and wrapping the earth wire around the armour.