Earth Rod size
Osprey
there any rule or decision factor that decides on the size to use …
standard 4’ rods come in 3/8” or 5/8”
Maximum current feed to installation is 32A
Colin Wilson
> there any rule or decision factor that decides on the size to use =3F
> standard 4=3F rods come in 3/8=3F or 5/8=3F
Bang enough in to ensure a low enough resistance. One might be enough
depending on the type of ground, sometimes twenty might be required.
John Rumm
The thicker ones are better if you need to use multiple lengths to get
enough depth. If however you can get to permanently wet clay within a
couple of feet like in these parts, the thinner ones are fine.
--
Cheers,
John.
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cynic
There is not "normally" a lot of difference in the thinner and thicker
rods performance but the thicker rods are physically more able to
drive straight if the ground contains stones etc. The ground
conditions do have a more considerable effect but your location is
critical to this, i.e. are you on dry well drained chalk or on
permanently damp clay.
You should ensure that the electrical characteristics meet the
requirements which will require at the very least an earth fault loop
impedance test carried out at the origin of your installation. Look
for less than 200 ohms to avoid instability due to drying/freezing. I
usually find the conditions in my location give between 20 and 40 0hms
(Loam over a bed of clay) but your situation may be completely
different.
It is also a good idea to use an earth rod chamber to make the final
connection to the rod as this will give protection and reduce the
surface voltage gradient in the event of a fault. It must provide
access to inspect the termination at intervals.
The conductor you use must be suitably selected/protected to avoid the
effects of corrosion and mechanical damage. Does your local library
have Regs Guidance notes in the reference section?
HTH
Steve Firth
> Does your local library have Regs Guidance notes in the reference
> section?
No need:
http://www.tlc-direct.co.uk/Book/5.1.1.htm
http://www.tlc-direct.co.uk/Book/5.5.2.htm
http://www.tlc-direct.co.uk/Book/8.6.1.htm
Ian White
>Osprey wrote:
>> Installing a small TT installation ... need to fit an earth rod … is
>> there any rule or decision factor that decides on the size to use …
>> standard 4’ rods come in 3/8” or 5/8”
>> Maximum current feed to installation is 32A
>
>The thicker ones are better if you need to use multiple lengths to get
>enough depth. If however you can get to permanently wet clay within a
>couple of feet like in these parts, the thinner ones are fine.
>
between the electrical performance of a 3/8in or a 5/8in earth rod. But
there may be other more important differences.
I use them with radio aerials, so unlike mains earth rods they sometimes
get pulled out and can be checked for corrosion. The 5/8in rods have
much thicker and better-quality copper plating, at least in my limited
experience.
All the 3/8in rods from Screwfix have turned into red rust within two
years. Both above and below ground, the thin copper plating was
completely gone. (I didn't measure their effectiveness as earth rods,
but dread to imagine.)
By contrast, after 10 years in the ground, a 5/8in rod made by Furse
came out looking almost like new. The only rust was where the point had
met a few stones, and most importantly those bare patches had not
spread. Furse have a proprietary bonding process, and the layer of
copper is also much thicker than on the cheap rods.
The 5/8in rods sold by TLC are almost certainly made by Furse (TL358):
http://tinyurl.com/6fayks
I don't know anything about TLC's 3/8in rods, but another point in
favour of the thicker ones is that they are much more rigid, and
therefore much easier to drive through underground obstructions they may
meet.
The bronze earth rod coupler for the 5/8in rods is also worth the money,
to avoid damaging the threads in case you need to go down deeper. It's
easy to make an adapter to drive the rods with an SDS drill (hammer
only).
--
Ian White
Rick Hughes
"Ian White" <I...@ifwtech.co.uk> wrote in message
news:ZkJTJ1Vq...@ifwtech.co.uk...
> John Rumm wrote:
>
> The 5/8in rods sold by TLC are almost certainly made by Furse (TL358):
> http://tinyurl.com/6fayks
>
That was the one I was intending to get
John Rumm
Yup, good choice. I have used the screwfix ones but they are nowhere
near as nice.
John Stumbles
> The bronze earth rod coupler for the 5/8in rods is also worth the money,
> to avoid damaging the threads in case you need to go down deeper. It's
> easy to make an adapter to drive the rods with an SDS drill (hammer only).
Or to make a pilot hole with one of those extra-long, thin SDS drill bits.
--
John Stumbles
87.5% of statistics are made up
Ian White
>On Wed, 23 Apr 2008 14:15:22 +0100, Ian White wrote:
>
>> The bronze earth rod coupler for the 5/8in rods is also worth the money,
>> to avoid damaging the threads in case you need to go down deeper. It's
>> easy to make an adapter to drive the rods with an SDS drill (hammer only).
>
>Or to make a pilot hole with one of those extra-long, thin SDS drill bits.
>
Yes, a pilot hole can be very helpful to clear the way for the rod. An
SDS drill bit is much better than the point of the rod for nudging
stones out of the way, and even breaking them up (it's surprising how
much impact energy does reach the far end of a metre-long bit) so the
pilot hole almost guarantees that you'll be able to sink a 1.2m rod at
least as far as 1.0m.
However, the pilot hole mustn't be too large, because a loosely-fitting
rod would have poor electrical contact with the ground. A 10mm bit will
make too large a hole for a 3/8in rod, so that is yet another reason to
step up to 5/8in. A 12mm bit is usually about the right diameter, giving
a nice firm fit for the rod.
--
Ian White
John Stumbles
> However, the pilot hole mustn't be too large, because a loosely-fitting
> rod would have poor electrical contact with the ground. A 10mm bit will
> make too large a hole for a 3/8in rod, so that is yet another reason to
> step up to 5/8in. A 12mm bit is usually about the right diameter, giving
> a nice firm fit for the rod.
Unless you're drilling into granite the soil is likely to collapse back
onto the rod within a short period so an oversize hole should not
permanently impair the effectivess of the rod.
--
John Stumbles
I'm more non-competitive than you
Ian White
>> However, the pilot hole mustn't be too large, because a loosely-fitting
>> rod would have poor electrical contact with the ground. A 10mm bit will
>> make too large a hole for a 3/8in rod, so that is yet another reason to
>> step up to 5/8in. A 12mm bit is usually about the right diameter, giving
>> a nice firm fit for the rod.
>
>Unless you're drilling into granite the soil is likely to collapse back
>onto the rod within a short period so an oversize hole should not
>permanently impair the effectivess of the rod.
>
That's true... but how long might you have before the electrical test?
BTW, I did try sinking a rod into almost solid rock, and even when the
ground was soaking wet it measured 630 ohms! Two years later, it had
come down to 580 ohms. Complete waste of time, but we keep it as a pet.
--
Ian White
Colin Wilson
> ground was soaking wet it measured 630 ohms! Two years later, it had
> come down to 580 ohms. Complete waste of time, but we keep it as a pet.
IIRC on substation "hot sites" sinking rods into holes filled with
rock salt helps...
John Stumbles
> BTW, I did try sinking a rod into almost solid rock, and even when the
> ground was soaking wet it measured 630 ohms! Two years later, it had
> come down to 580 ohms. Complete waste of time, but we keep it as a pet.
You'll deserve all you get from the bunny-huggers if you keep your pets
buried up to their necks in the ground :-)
--
John Stumbles
Extreme moderate