TT...installing 5/8" rods

[GLENNSPARK]

well...here I am again...this time its installing a TT system utilising 2X 5/8" rods...with the connector..:


here is the necessary gear as laid out (the 20mm PVC conny isn`t in the pic)


these are the type of rods you need...no 3/8" twigs here (apart from in that bush behind maybe)


site is about 1 1/2 meters away from the house...thats the first one in..now to connect the second onto the first ....and carry on...


still some way to go...


get it brayed in....Robert my assistant uses the fork with a bit of tape to keep the rod steady


thats a length of 10mm CSA G/Y being pulled through a length of conny for main earthing (the conny was dropped into the ground)

Ze was OK at just over 15 ohms...had to change the 16th edition setup in the board...it was configured as a split load 10 & 2....dropped another RCD in it and did it 5 & 5
happy days...:biggrin:

 

[Knobhead]

As a relatively inexperienced spark what is the appeal of a 5/8 over the thinner rods?

I have only ever installed a handful of new rods and always use the 5/8 mainly because they are obviously stronger. The surface area is not that much greater so does not make much difference to Ra when compared to a thinner rod.

So it is just a strength thing i.e. they can take a better hammering to get them deep enough....

1.667017 Greater to be precise.

 

[Richard Burns]

1.667017 Greater to be precise.

3/8 compared to 5/8 must be 1.666666666666 recurring surely?

 

[Silly Sausage]

You need a 6 with a dot on it's head there.

 

[PEG]

I knew this rod-appreciation thread couldnt last,may i suggest a duel in the morning,if swords are a problem,use two rods,where i might advise in this rare instance the lighter one would give advantage...:hurray:

 

[NDG Elecs]

1.667017 Greater to be precise.

Yeah, but that makes little difference to the Ra. Might reduce 20 ohms to, say, 16 ohms... I have not done the maths as you can tell!

Having never used the thinner rods I do not know....do they bend far too easily....I read recently that diameter itself has a marginal effect, other factors such as soil type, chemical composition (salts etc), water table, multiple rods and using marconite backfills are much more relevant to reducing Ra.

Ta.

 

[Richard Burns]

Yeah, but that makes little difference to the Ra. Might reduce 20 ohms to, say, 16 ohms... I have not done the maths as you can tell!

Having never used the thinner rods I do not know....do they bend far too easily....I read recently that diameter itself has a marginal effect, other factors such as soil type, chemical composition (salts etc), water table, multiple rods and using marconite backfills are much more relevant to reducing Ra.

Ta.

The thin rods will bend easier and in hard soil can be a problem, it is amazing how much a 66.7% increase in surface area can make a difference. (notice how I slipped in that Tony was right without admitting it).

That said the other factors will probably override in many cases. Easier to put in and you have the fittings for them to be extended.

 

[Engineer54]

As a relatively inexperienced spark what is the appeal of a 5/8 over the thinner rods?

I have only ever installed a handful of new rods and always use the 5/8 mainly because they are obviously stronger. The surface area is not that much greater so does not make much difference to Ra when compared to a thinner rod.

So it is just a strength thing i.e. they can take a better hammering to get them deep enough....

The thin short 3/8'' twigs can't be extended, so will not provide much, if any stability to a TT system, likewise with a single 5/8'' rod. As a minimum, on any TT system two 1.2m coupled 5/8'' rods should be driven into the ground, which will in most circumstances, give you a low Ra value and provide the all important stability to the system. So it's not just the strength thing.

I can't personally remember ever using 5/8'' rods, and i've never actually seen a 3/8'' rod. I'm used to using 2.4m and 3.2m 3/4'' earth rods....

 

[Silly Sausage]

It's starting to sound like a cock measuring exercise!

 

[NDG Elecs]

OK, thanks chaps.

I did not realise the twigs could not be extended. My first TT was at my own house. The house is a Edwardian terrace built on a outcrop of bedrock. The row of houses themselves are four feet up from pavement level. I only managed to get approx. 1.2m-coupler-0.7m (so 1.9m depth) in before it would not budge anymore. Ra hovers around 30ohms. Should ideally put another rod in, or maybe some other solution.....solution=not urine!

 

[PEG]

Agreed,it's not the diameter of your rod,it's the depth of penetration in virgin mother earth.....Wonder if Eng has the gimp out of the box yet? :sweatdrop:

 

[Marvo]

It's starting to sound like a cock measuring exercise!

Some people measure their cock in meters rather than centimeters.



I assume that's what you meant Archy as this is in the public forums after all.

 

[Silly Sausage]

I remember watching some film once with a young firm chickatica, the subtitles said 'I am 12 long', suddenly felt very small until I realised it was frog talking centimeters.

 

[Geordie Spark]

Q. What's the definition of an early bird?


A. A girl who wakes up at cock grow.

 

[Engineer54]

OK, thanks chaps.

I did not realise the twigs could not be extended. My first TT was at my own house. The house is a Edwardian terrace built on a outcrop of bedrock. The row of houses themselves are four feet up from pavement level. I only managed to get approx. 1.2m-coupler-0.7m (so 1.9m depth) in before it would not budge anymore. Ra hovers around 30ohms. Should ideally put another rod in, or maybe some other solution.....solution=not urine!

You could always try driving another rod position in further down the garden, but 30 ohms and a 1.9m depth is far better than the numpty 200 ohms suggested in the BGB!!

 

[NDG Elecs]

As you can tell I am sober tonight, hence boring!

Just found the bit I read from originally. It's a Megger publication called Getting Down To Earth from 2005.
It says that doubling the girth, ahem, diameter reduces Ra by approx 10%. So diameter not that important.

I have a PDF copy of GDTE on my laptop, looks quite interesting if that sorta thing floats ya boat. Dont know or recall how I got it. Maybe Megger website, not sure.