Connecting earth rods

[Taylortwocities]

..............being started as an overgroud service (Metropolitan)
You should read this http://www.amazon.co.uk/Metropolitan-Line-Illustrated-History/dp/1854142755 and you will see that well before the turn of the century the underground sections were up and running.

The Inner Circle line (all underground) opened in 1884.

You were the one that mentioned 40 years!

 

[ban-all-sheds]

How would a communication earth rod earth affect a tube train in 1863 when the first phone conversation took place in 1876.

-. . ...- . .-. .... . .- .-. -.. --- ..-. - .... . - . .-.. . --. .-. .- .--. .... --..-- .-- .... .. -.-. .... .--. .-. . -.-. . -.. . -.. .--. .... --- -. . ... -... -.-- .- --. --- --- -.. ...-- ----- -.-- . .- .-. ... ..--..

 

[Taylortwocities]

Indeed. Telegraph, and later, cablecode transmission was all signalled with reference to earth.

 

[1john]

How would a communication earth rod earth affect a tube train in 1863 when the first phone conversation took place in 1876.

-. . ...- . .-. .... . .- .-. -.. --- ..-. - .... . - . .-.. . --. .-. .- .--. .... --..-- .-- .... .. -.-. .... .--. .-. . -.-. . -.. . -.. .--. .... --- -. . ... -... -.-- .- --. --- --- -.. ...-- ----- -.-- . .- .-. ... ..--..

Care to translate squire?

 

[Monkeh]

What, you can't read morse?

 

[1john]

Nope, I was never taught it

 

[Gees]

It would seem that it can make it higher, as they interfere with each other if they are too close.
Have a peek at http://ecmweb.com/mag/electric_bringing_grounding_down/ and scroll down to "Ground Rod Spacing"

The total resistance cannot be increased by adding rods, regardless of where those rods are. That website actually states

The overlap increases the net resistance of each rod

which is very different from increasing the combined resistance of the set of rods.

Two rods located very close together will be virtually the same as a single rod. As the distance between the rods is increased, the total resistance measured when the rods are linked together will reduce.

Thats what I thought but good old BAS is at odds with mister OHM regarding resistors in parallel..

 

[Gees]

The best method is to install a longer (extension piece) or use a thicker rod.

If you use a second rod it must be at a distance more than the other rod according to this article http://www.keison.co.uk/furse/furse20.htm

BS7430 apparently says 2.2 times the driven depth between each rod . So it looks like the further apart the better.

There is a lot of scary formulae on this. If you can't get to sleep have a gaze at
this!


Gees, re

I would think that ANY distance is sure to lower the ze. It cannot make it higher....

It would seem that it can make it higher, as they interfere with each other if they are too close.
Have a peek at http://ecmweb.com/mag/electric_bringing_grounding_down/ and scroll down to "Ground Rod Spacing"

What fun, hey?

What it says is the impedence of two closely spaced rods would be higher that two widely spaced rods, NOT more than a single rod.

 

[ban-all-sheds]

Thats what I thought but good old BAS is at odds with mister OHM regarding resistors in parallel..

Not if when you put them in parallel the values of the individual resistors change.

What it says is the impedence of two closely spaced rods would be higher that two widely spaced rods, NOT more than a single rod.

What it says is "The overlap increases the net resistance of each rod, making the grounding electrode system less effective than if the rods were spaced farther apart".

I would think that ANY distance is sure to lower the ze. It cannot make it higher....

So if the interference drives up the resistance of each individual rod I don't think there is a cast iron guarantee (or even an extruded copper one) that 2 rods won't be worse than one.

 

[maltaron]

Whilst I will not join the argument regarding increase or decrease of efficiency of multiple rods, It should be pointed out that for the purpose of earthing rods for AC mains the measurement is IMPEDANCE not resistance, which is a DC measurement, and they can be considerably different. A perfect example of this is a loudspeaker voice coil, normally a nominal 8 ohms. Measured with a DC ohmmeter it will show almost short circuit but measured with an impedance meter the reading will be around 8 ohms, varying with frequency. Also for AC circuits where the earth conductor runs parrallel to another earthed surface inductance will affest it.

 

[ban-all-sheds]

Earth tapes are usually more effective than earth rods, but mean digging a trench. Laying a hard drawn copper conductor (50 or 70mm really) into a trech can give very low readings.

How deep should a tape be in clay soil?

And how do you connect to it? Presumably not below ground for reasons of accessibility of the connection for inspection. (OTOH it'd be fun to use one of those thermite kits ) Inside a small inspection chamber like an earth rod pit? Bring the tape up above ground and connect it there?

 

[Spark123]

Bring the tape up above ground and connect it there?

Yep, probably the best way to do it.

Re the earth rods, even if you get the rods far enough apart so the voltage pools don't cross, having two rods of equal resistance will not halve the result as the means of earthing is in the earth fault loop impedance path which will always remain in series with the two rods.

 

[Gees]

Thats what I thought but good old BAS is at odds with mister OHM regarding resistors in parallel..

Not if when you put them in parallel the values of the individual resistors change.

What it says is the impedence of two closely spaced rods would be higher that two widely spaced rods, NOT more than a single rod.

What it says is "The overlap increases the net resistance of each rod, making the grounding electrode system less effective than if the rods were spaced farther apart".

I would think that ANY distance is sure to lower the ze. It cannot make it higher....

So if the interference drives up the resistance of each individual rod I don't think there is a cast iron guarantee (or even an extruded copper one) that 2 rods won't be worse than one.

What if I where to drive in ,lets say 10 rods all within inches of one another. Would the impedence then be very much higher than a single rod? or would it be the equivalent of a thicker single rod?

 

[Taylortwocities]

What if I where to drive in ,lets say 10 rods all within inches of one another. Would the impedence then be very much higher than a single rod? or would it be the equivalent of a thicker single rod?

That depends on a lot of factors. Are those rods in a line, or a square, or a ring, or a star.
How about if they were laid out horizontally at a shallow depth?

This is the sort of thing you'd have to consider - and end up with having to work though this

Untitled

• Taylortwocities
• 27 Sep 2010
• 1

read all about it at this interesting cure for insomnia

 

[Gees]

What if I where to drive in ,lets say 10 rods all within inches of one another. Would the impedence then be very much higher than a single rod? or would it be the equivalent of a thicker single rod?

That depends on a lot of factors. Are those rods in a line, or a square, or a ring, or a star.
How about if they were laid out horizontally at a shallow depth?

This is the sort of thing you'd have to consider - and end up with having to work though this

Untitled

• Taylortwocities
• 27 Sep 2010
• 1

read all about it at this interesting cure for insomnia

All in a bunch ( almost touching )