Did a re wire on a village hall TT system , after reading the threads on rods i went for it, chucked away the 3/8 twig coupled together 3 5/8 rods and away i went driving away with my 4lb lump hammer 3.6m of depth and got my ZE down to 14 ohms so i guess thats a ok reading for a TT well bellow the 200 ohms , but was hoping it would be a lot lower...
- Thread starter huntos33
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S
sparks1973
well next time send it down with a rotary hammer set to hammer only......
Good on you. A ZE of 14ohms is pretty good, sometimes 1 extra rod gives a drastically better reading especially if you get below the local watertable level. Maybe invest in an SDS attachment for you jackhammer, it's a lot easier than a 4lb hammer
The exercise did me good, think in this instance though the water table is a long way off a small village perched in the top of the cotswold hills but the attachment sounds a good idea going forward
Not so, there are springs all over the Cotswold hills, but I'm surprised that you were able to drive an electrode into the ground so far by hand since the soil is so rocky.
S
sparks1973
get a bit of bar end....say 1" dia...about 2" long....and just get someone with a drill to spotface it on one end about 1/2" deep with a drill the same diameter as the protective caps that you get with threaded earth rods then have a little sesh with the stick plant and weld it onto an old SDS shank...THERE! jobs a gud un...
Tried with an SDS homemade attachment (previously worked in engineering so it wasn't heath robinson) didn't do much so I gave up and got the 1 1/2 lb 10'' long handle lumphammer I usually use and got three rods deep in 5 mins.
you need an SDS Max or jackhammer ,normal SDS drill nowhere near enough power, all the force just causes a lot of vibration and not much penetration.
(NB for all the house bashers this 1 1/2 lb hammer looks like a toy compared to the anvils on sticks I see people using which are really only meant for bashing bricks to pieces, and the users usually have very little control which usually means lots of effort for little result, and quite often injuries occur, a smaller one will work just as well, but its about technique and directing the energy in the right place and letting the hammer do the work. I've convinced several people who've got one arm twice the size of the other and a few mangled fingers by going head to head on chasing for boxes and driving rods in.)
I saw a post about a homemade slide hammer design for earth rods which did look very good ,might have ago at one myself.
out of curiosity does anybody ever check for cable before knocking rods in?
you need an SDS Max or jackhammer ,normal SDS drill nowhere near enough power, all the force just causes a lot of vibration and not much penetration.
(NB for all the house bashers this 1 1/2 lb hammer looks like a toy compared to the anvils on sticks I see people using which are really only meant for bashing bricks to pieces, and the users usually have very little control which usually means lots of effort for little result, and quite often injuries occur, a smaller one will work just as well, but its about technique and directing the energy in the right place and letting the hammer do the work. I've convinced several people who've got one arm twice the size of the other and a few mangled fingers by going head to head on chasing for boxes and driving rods in.)
I saw a post about a homemade slide hammer design for earth rods which did look very good ,might have ago at one myself.
out of curiosity does anybody ever check for cable before knocking rods in?
E
Engineer54
I bet that when you first started driving in the first rod, it was swinging around all over the place using a lump hammer!! lol!! Anyway now for the good news, ...Because the rod couplers have a greater diameter than the rods themselves, the ground soil, is not as yet consolidated around the top two rods. So you can expect that 14 ohm Ra value to get considerably better over the next 12 to 18 months as that ground compacts and consolidates around those two upper rods... One things for sure, you will have created a very stable TT system, and a system that will only improve over the coming months....
Well Done!!!
That was a serious question , a friend of mine lives on the south coast and told me he knew of a case where someone knocking a rod in went through a 240mm cable, it penetrated 2 phases and he received serious burns and some fragments of the exploding cable injured his legs,
for example if you are digging a trench then the obvious thing is to use a cable locator to check for hidden utilities yet no one seems to think twice about knocking a rod in without checking whats below them.
surely he would have penetrated the earthed sheath first?
E
Engineer54
A 240mm SWA cable is in all likelihood, going to be a DNO cable, unless on an industrial or large commercial site. So in that instance there should have been cable protection tiles (usually 10'' X 10'' concrete paver's) so he should have known that he had hit something quite solid. Bit foolish to carry on thumping away, without making some kind of investigation. It's not as if he'd gone down that far before hitting that protection tile....
S
StuSpiers
Just created a blog of my last Spike install.
How To install An Adequate Earth Spike - Blogs - Electricians Forum | Electrical Advice Forum | An electrical forum for electricians in the UK | Electricians Forum
Was a beauty!
How To install An Adequate Earth Spike - Blogs - Electricians Forum | Electrical Advice Forum | An electrical forum for electricians in the UK | Electricians Forum
Was a beauty!
M
Marvo
I'm glad people are getting a bit more excited about achieving a decent TT earth, I think it's a worthwhile thing not to put all your eggs in one basket relying on the RCD because of a poor Ra.
Maybe with the growing interest they'll do end users everywhere a favour and amend the regs at some stage in the future.
Maybe with the growing interest they'll do end users everywhere a favour and amend the regs at some stage in the future.
Last edited by a moderator:
K
KevinS
"all the force just causes a lot of vibration and not much penetration."
Nothing worse!
Read more: http://www.electriciansforums.net/e...62028-5-8-earth-rod-debate.html#ixzz23wNSb5ie
Nothing worse!
Read more: http://www.electriciansforums.net/e...62028-5-8-earth-rod-debate.html#ixzz23wNSb5ie
M
MarkieSparkie
T
trev
Good article mate, one criticism though. The ones who don't know how to create a good TT system may have a few why questions.
Such as, why come away from the building 2 metres? Well we know that the area you're avoiding will probably be filled with the builder's rubble but the uninitiated may not.
E
Engineer54
A good effort at bringing some important factors together for the benefit of those that are inexperienced in providing a TT system...
I am however, having problems with the Ra values you gained. The only exception, would be if the area is or was at one time a salt marshland. I see that you were using a MFT to measure Ra values, one that i take has a 3 pole earth test facility. Did you check these values you gained, with a Ze type ELI test at the service head position (MET) with the bonding conductors disconnected etc?? Without knowing what distance your axillary/temporary current test rod (Y) was placed and the distances your voltage test rods (Z / Z1 / Z2) were placed, i can't really comment. Only that they do need to be placed in a relatively straight line, the greater the distances, and the more points the Z rod/spike is tested (normally 3 points but better with 5, ...''eg 50% -10 / -20% / +10% / + 20%'') the more accurate the values obtained will be. It's fine to water in the temporary rods, but never the earth rod/electrode under test!! I doubt very much that your Ra value will half in the course of just one day, it takes a number of months for ground soils to consolidate around driven rods.
imago
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True, but there's another factor to consider with the distance from where builing work was carried out. Most of the chemicals and mixes used (cement, plaster etc) are alkaline. Not only are they affecting the soil pH level during building work, but the affect the pH level as the rain runs through the brickwork and concrete. Alkaline soil has less hydrogen ions in it and is less conductive than acid soils. So the distance away from the building is more about chemical differences in the soil as it is about rubble.
At two metres from the building you are at a point where you can reasonably expect the soil conditions to be at 'normal' levels for the area.
S
StuSpiers
Ze seemed very low to me also (that's kinda why I used it as an example)
On reflection though when you take the ground conditions into account the recent weather it isn't so strange.
This house was inset into a hill - the hill had been excavated to build the house.
The hill seemed to be a deposit of pure clay.
It was and appeared to be perpetually wet - the area was completely shaded but still open to the rain and deep moss was everywhere.
I only use ELI method for Ra readings, parallel paths would have been removed for Ze yes.
I appreciate it isn't the most accurate method of testing Ra and that's probably why I got inconsistency between the readings.
On reflection though when you take the ground conditions into account the recent weather it isn't so strange.
This house was inset into a hill - the hill had been excavated to build the house.
The hill seemed to be a deposit of pure clay.
It was and appeared to be perpetually wet - the area was completely shaded but still open to the rain and deep moss was everywhere.
I only use ELI method for Ra readings, parallel paths would have been removed for Ze yes.
I appreciate it isn't the most accurate method of testing Ra and that's probably why I got inconsistency between the readings.
E
Engineer54
[QUOTEI only use ELI method for Ra readings, parallel paths would have been removed for Ze yes. ][/QUOTE]
So what was you using the MFT at the rod position for then??? I'm still sceptical with your ultra low Ra values, especially with just 2 rod's, but no doubt that it will provide a stable TT system. Maybe you have hit the Ra jackpot, in achieving a better than TN value, and hope that you Have. But there is this feeling, that's telling me something is not quite right....
Perhaps, if it's at all possible, you could test this rod on a regular basis say every couple of months or so. at the very least it will show you just how stable your Ra value is...
Clay can be a good soil for TT systems, but can dry out very quickly too, all depends on what type of clay it is. If this hill is all clay, i doubt if they would have built a house on it, too much of a risk of subsidence.
So what was you using the MFT at the rod position for then??? I'm still sceptical with your ultra low Ra values, especially with just 2 rod's, but no doubt that it will provide a stable TT system. Maybe you have hit the Ra jackpot, in achieving a better than TN value, and hope that you Have. But there is this feeling, that's telling me something is not quite right....
Perhaps, if it's at all possible, you could test this rod on a regular basis say every couple of months or so. at the very least it will show you just how stable your Ra value is...
Clay can be a good soil for TT systems, but can dry out very quickly too, all depends on what type of clay it is. If this hill is all clay, i doubt if they would have built a house on it, too much of a risk of subsidence.
P
PEG
I'm with you on the regular testing bit re;earth electrodes,did a post a while ago concerning this.If any lads had done or had knowledge of electrode install and then could give conditions and test results over time,it would give an idea of whats good and what varies,just a thought....But stop scaring my missus with the clay/subsidence stuff! Mines on clay (blue) and not moved since 1937.Took 45 tonnes out for rainwater tank in garden.It's like IRON.Get your point with other types,ground heave etc just off to give her a calmer......:wink5:
Yes it was a DNO cable and there were no tiles or tape and the depth of the cable was 320mm below the surface cable was installed in 1995
and in regard to a different post, as I'm sure most of us will appreciate irrespective of the earthed sheathing if the cable is penetrated it goes bang!
A firm I have subbed to also hit a cable some time ago again the cable was just below the surface approx 380mm and again no markers or tape and when the DNO sent their repair bill they challenged it with the fact that the cable was not deep enough
The Dno replied that due to ground settlement and erosion that cables can end up closer to the surface ,this seems unlikely as this cable had been in the ground for about 15 years, its actually a sheltered housing type of development and the cable route was through the middle of the garden and it is obvious that there has been no abnormal, if any erosion and only normal settlement, they also said that the absence of cable markers or tiles could be down to cables being installed by the use of a Mole machine, but the Director of the trust an ex civil engineer said the ground was excavated and cable laid and he has photos to prove it, which he took as the project progressed.
Anyway the company involved had their H&S consultant look at it and he's reported it to the HSE who are investigating the Dno for similar occurences, but I would imagine that the HSE would be duty bound to investigate the company's safe working practice as they were using builders plans which were vague and they never used a cable tracer and were using a pick and shovel, which is pretty much what led me to ask the question whether others scanned the ground before knocking the rods in ie if you do put a rod through a cable then the owner of a business is going to be liable for repair costs and fines at the very least.
M
Marvo
Working in Africa it's probably different in many respects to the UK. The safest place to knock a rod in here is exactly where the drawing shows a supply cable, I've never seen a council drawing that's accurate in over a decade and that's assuming there actually is a drawing.
Seriously I would always excavate at least 600-700mm and often a full meter with a spade before starting a rod in the ground. Also if I hit something solid in the first meter of driving the rod in I will stop and try again about a foot away. It's not 100% foolproof and there's always a nagging doubt in my mind that there could be services but after 1.5 meters below ground level it's highly unlikely. I would certainly agree with their statement though that ground levels can change radically over time. We've been back to a couple of jobs years later where we installed cabling at 1 meter depth and it's become exposed on the surface.
Seriously I would always excavate at least 600-700mm and often a full meter with a spade before starting a rod in the ground. Also if I hit something solid in the first meter of driving the rod in I will stop and try again about a foot away. It's not 100% foolproof and there's always a nagging doubt in my mind that there could be services but after 1.5 meters below ground level it's highly unlikely. I would certainly agree with their statement though that ground levels can change radically over time. We've been back to a couple of jobs years later where we installed cabling at 1 meter depth and it's become exposed on the surface.
E
Engineer54
In both the instances you gave in your post, the DNO responsible will be cited for gross negligence if the burial depth does not adhere to their own publicised depths, and additionally installed with no warning tape or protective tiles. This is ''Standard Practice'' when all said and done, where cable(s) pass or are installed in public area's
Cable burial depths are actually increased where they are run through gardens etc where there is a higher likelihood of soil disturbance due to digging etc...
Now anyone driving an earth rod in the ground that hit's something solid (cable tile etc) will if they had any sense stop an do a little investigating before thumping their way through it. If your unsure if any services are in that area, then excavate 500mm or so, and then drive your rod in....
Cable burial depths are actually increased where they are run through gardens etc where there is a higher likelihood of soil disturbance due to digging etc...
Now anyone driving an earth rod in the ground that hit's something solid (cable tile etc) will if they had any sense stop an do a little investigating before thumping their way through it. If your unsure if any services are in that area, then excavate 500mm or so, and then drive your rod in....
Interesting to read about digging pits first, i assume this is not always possible but seems sensible i must admit i spent some time checking and was happy i would be safe where i was overhead supplies etc. This forum has opened my eyes to TT systems as i normally work in the retail area so when i have done the odd domestic job it's always been a twig, now im SE and doing more so it's been of a great help finding this forum, keep up the good work mods and members.
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