Earth rod for outhouse


M

mark

I need to install an earth rod for an outhouse.
The ground is seriously rocky and getting an 8' rod into the ground is
not going to be easy.
I seem to remember reading that reinforcing bars in concrete provide a
pretty good earth, this would be a lot easier to achieve than drilling
an 8' hole in the ground.
Would several shorter rods wired together be sufficient?
Burying several meters of copper pipe to mimic the old water main earth?
 
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B

BigWallop

mark said:
I need to install an earth rod for an outhouse.
The ground is seriously rocky and getting an 8' rod into the ground is
not going to be easy.
I seem to remember reading that reinforcing bars in concrete provide a
pretty good earth, this would be a lot easier to achieve than drilling
an 8' hole in the ground.
Would several shorter rods wired together be sufficient?
Burying several meters of copper pipe to mimic the old water main earth?

Mark Roberts
Proper earth rods are only a metre in length, or there abouts, and you need to
join them together with the right kit. You also need to buy a driving stud that
screws on the end of the rod, so the hammering doesn't damage the thread of the
screwed end of the rod.

What were you thinking using instead?
 
B

BigWallop

mark said:
I need to install an earth rod for an outhouse.
The ground is seriously rocky and getting an 8' rod into the ground is
not going to be easy.
I seem to remember reading that reinforcing bars in concrete provide a
pretty good earth, this would be a lot easier to achieve than drilling
an 8' hole in the ground.
Would several shorter rods wired together be sufficient?
Burying several meters of copper pipe to mimic the old water main earth?

Mark Roberts
Found a link to a .PDF file that shows what proper earth ground rods look like
for you. You'll need a .PDF reader for the pages.

The link: http://www.keison.co.uk/furse/pdf/earthing/earthing_rods.pdf
 
I

Ian White

mark said:
I need to install an earth rod for an outhouse.
The ground is seriously rocky and getting an 8' rod into the ground is
not going to be easy.
And probably not much good either IME.
I seem to remember reading that reinforcing bars in concrete provide a
pretty good earth, this would be a lot easier to achieve than drilling
an 8' hole in the ground.
Would several shorter rods wired together be sufficient?
"Ufer grounds" are used in the USA (Google for the phrase) but they
don't seem common over here.
Burying several meters of copper pipe to mimic the old water main earth?
At my place, the ground is so rocky that even if you can get an earth
rod in, the resistance is too high to be useful. The water main is the
only effective earth connection.

If you bury a pipe to mimic a water main, it should be below the frost
line (just like a real one) because the resistance rises considerably
when the groundwater freezes.
 
M

Mike

mark said:
Thats very helpful.
But the problem is the rocky ground. A lot is made up ground and the
rest is shaley dry stuff. It's not the best stuff in the world for
conductivity.
I need more contact if you see what I mean with as much ground as
possible.

Dig a pond and throw the wire in ?
 
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A

Andy Dingley

But the problem is the rocky ground. A lot is made up ground and the
rest is shaley dry stuff. It's not the best stuff in the world for
conductivity.
There's a US army kit perfect for installing such things. It involves a
shaped charge to blow a hole in any surface crust or concrete, then a
downwards-pointing rocket motor to drive the earth rod (or anything you
might like) deep under the surface.

I've only seen one of these things in the flesh, and they wouldn't let
me push the button 8-(
 
B

BigWallop

mark said:
Thats very helpful.
But the problem is the rocky ground. A lot is made up ground and the
rest is shaley dry stuff. It's not the best stuff in the world for
conductivity.
I need more contact if you see what I mean with as much ground as
possible.
I'm sure there's a knowledgeable person somewhere who knows more about
this than I do.


Mark Roberts
I'm sure if you go deep enough, three, four or five rods deep, you'll get
somewhere close to a proper earth ground connection. :)

You can also use a ground plate to make a good earth ground source. Scrape the
top layers off, maybe two or three feet down, and lay in a steel plate to
connect the earth terminals to. Then fill it back over. A plate of four or
five foot square would probably be enough. Any scrap yards near you? Old flat
steel plate of something close to a half inch thick is what you want.

Or you could go with two or three rod sites to spread the load around them. You
have to use at least 25 mm csa' conductors to bond these sites together though.

(csa' = cross sectional area)
 
B

BigWallop

Andy Dingley said:
There's a US army kit perfect for installing such things. It involves a
shaped charge to blow a hole in any surface crust or concrete, then a
downwards-pointing rocket motor to drive the earth rod (or anything you
might like) deep under the surface.

I've only seen one of these things in the flesh, and they wouldn't let
me push the button 8-(
Sounds like a very handy kit. Where can I obtain them? :)
 
B

BigWallop

chris French said:
Ebay ? :)

Chris French
Got one on a Buy it Now, and the postage was free all the way from Iraq. The
sellers name was Sunny Shi'ite or somethin' like that. Brilliant!!! Everybody
should have one.

ROFLMAO!!!!
 
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M

Martin Angove

In message <[email protected]>,
mark said:
I need to install an earth rod for an outhouse.
The ground is seriously rocky and getting an 8' rod into the ground is
not going to be easy.
Just as a thought, do you *have* to install an earth rod? If the shed is
close enough to the house and you use thick enough wire you could quite
safely "export" the house earth under most circumstances, but it's a
function of impedance/distance etc.

Hwyl!

M.
 
I

Ian White

mark said:
[...]
But the problem is the rocky ground. A lot is made up ground and the
rest is shaley dry stuff. It's not the best stuff in the world for
conductivity.
Cancel my previous - if it's only made ground and "shaley dry stuff ",
you have a very good chance of sinking 1m rods using a 1000x10mm or
1000x12mm SDS bit to drill a pilot hole. The reason for recommending
drilling first is that it can easily break up stones that would stop an
earth rod if you simply tried to hammer it.

For driving the rod, use the SDS drill with rotary stop, and a 0.5in
square drive adapter. An appropriate sized socket will keep it centred
on the rod. This works *much* better than just 'itting it wiv an 'ammer.

However, the earth rod is typically 1.2 m long while the drill bit is
only 1.0m... so for that last 0.2m you're on your own. Be prepared to
cut your losses using an angle grinder.

If you feel the drill bit breaking up significant amounts of hard stuff
down to 1.0m, then you've no chance of being able to sink a
double-length rod. The only exception might be if you're going to break
through into softer, rock-free ground (eg if it's a layer of made ground
covering clean, soft clay).
I need more contact if you see what I mean with as much ground as
possible.
As much *wet* ground as possible, you mean. With really rocky ground, it
can actually get drier further down, with most of the groundwater
flowing in the looser top layers.

If that is the case for you, you would get a better earth connection
from two 1.2m rods than by making heroic efforts to sink a whole 2.4m.
(Space the 1.2m rods at least 2.4m apart, or else you'll not get full
benefit.) Better still, go horizontal as you yourself suggested.

In the end, it all depends on exactly where *your* groundwater is.
 
M

mark

Martin Angove said:
In message <[email protected]>,


Just as a thought, do you *have* to install an earth rod? If the shed is
close enough to the house and you use thick enough wire you could quite
safely "export" the house earth under most circumstances, but it's a
function of impedance/distance etc.
You might be right there.
There is 12m of 25mm diameter armoured cable.
I guess if I clamp the armour in a brass gland in the steel consumer
unit box in the house and do the same at the shed (also a steel consumer
unit) it would suffice.
Would testing the earth; by seeing if an RCD works when connected in the
shed, prove the earth is sufficient?
 
J

John Rumm

Ian said:
For driving the rod, use the SDS drill with rotary stop, and a 0.5in
square drive adapter. An appropriate sized socket will keep it centred
on the rod. This works *much* better than just 'itting it wiv an 'ammer.
Now that is a good idea! (I need to stick a rod in tommorow...)

Don't spose you know any good tips for making really sure you don't
stick it through either the gas or water mains?
 
M

Martin Angove

In message <[email protected]>,
mark said:
You might be right there.
There is 12m of 25mm diameter armoured cable.
I guess if I clamp the armour in a brass gland in the steel consumer
unit box in the house and do the same at the shed (also a steel consumer
unit) it would suffice.
Would testing the earth; by seeing if an RCD works when connected in the
shed, prove the earth is sufficient?
No, because testing the RCD doesn't test the earth at all. Most RCDs
don't even have an earth connection. A good first step is to do a few
calculations (see below). Testing with the proper gear is a good second
step. Getting it all certified as per Part P is the finishing touch.
(Usual disclaimer; you do realise that all outdoor work / new circuit
work now comes under Part P and should be notified to Building Control
before work is started?)

25mm diameter armoured cable is what csa per conductor? How many
conductors of what cross sectional area is the important question. 12m
doesn't sound too far to me, so long as the cable is chunky enough -
let's face it, there are likely to be circuits in your house with longer
runs than that. What earthing system does your house have? What size and
type is the protective device at the house end (i.e. fuse or MCB)? What
sort of distribution will you have at the shed (fuses/MCBs etc.)? To
what uses will the supply in the shed be put?

As for the actual earth connection, if it's two-core SWA and you are
using the armour as earth (easier to use 3-core) then you need to use
the proper glands and if you can't guarantee that the boxes are properly
connected to earth at each end (metal consumer units should be, but
worth checking) you'd be as well putting in a chunky wire too, connected
to a tag on the cable.

HTH

Hwyl!

M.
 
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I

Ian White

John said:
Now that is a good idea! (I need to stick a rod in tommorow...)

Don't spose you know any good tips for making really sure you don't
stick it through either the gas or water mains?
Well, it is "tomorrow" now. Probably by the time you read this, it'll be
all over...

If we were talking about the main service earth spike on a TT system,
then that's a very good point, because in many cases all the services
tend to come in pretty close together.

And don't forget the sewer pipes and any soakaway drains.
 
J

John Rumm

Ian said:
Well, it is "tomorrow" now. Probably by the time you read this, it'll be
all over...
It would be if only it would stop peeing down for long enough for me and
my trusty SDS to venture out ;-)
If we were talking about the main service earth spike on a TT system,
yup

then that's a very good point, because in many cases all the services
tend to come in pretty close together.
yup!

Gas main rises right about level with the meter cupboard. One might
presume that it is safe to sink it behind this point, however a slight
concern is the neighbouring propery has a similar rising main a few feet
further back. Hence the question: how likely is it that they would feed
a pipe to ours, tee upward, carry on for a bit then turn right and head
over to the neighbours!

Water maiun must go past - but that is probably only half inch so a
smaller target!
And don't forget the sewer pipes and any soakaway drains.
I think I am clear of those in the intended position (although they
become more of an issue if I try to avoid the other services by going
further away)
 
A

Andy Wade

Martin said:
Testing with the proper gear is a good second step.
In the absence of a fancy earth tester[1], the following simple DIY
procedure that I've posted a couple of times before will give results of
entirely adequate accuracy:

[Repost from 20/04/1998, Message-ID: <[email protected]>]
Anyone with a bit of electrical common sense, knowledge of Ohm's law,
and a decent multimeter can measure earth electrode resistance quite
easily. You need to isolate the electrode in question and then find a
way of getting some current to flow into it. A safe way to do this is
to use a double-wound mains transformer with a secondary voltage of
around 24 (exact value not critical). Connect one end of the secondary
via a suitable length of wire to the main earth terminal in the house
and connect the other end to your earth electrode via an ammeter.

Energise the primary of the transformer, and the secondary current which
flows will immediately give you a rough idea of the total resistance in
the circuit, most of which will be attributable to your electrode. For
a more accurate result, drive a second temporary earth electrode (a 2ft
offcut of 15mm water pipe will do) into the ground at a distance of 10m
or more from the one you're measuring. Then use the meter on volts to
measure the voltage drop between the two electrodes. Dividing this
figure by the electrode current measured earlier gives you the earth
resistance. (Reactance in the circuit will be negligible.) Move the
temporary reference electrode to a second position and repeat. Average
the two values obtained, but if they are significantly different, try
further positions for the reference electrode.


[1] Not to be confused with a loop tester for measuring earth fault loop
impedance, which *is* an indispensable piece of kit.
 
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D

Dave Plowman (News)

I need to install an earth rod for an outhouse.
The ground is seriously rocky and getting an 8' rod into the ground is
not going to be easy.
I seem to remember reading that reinforcing bars in concrete provide a
pretty good earth, this would be a lot easier to achieve than drilling
an 8' hole in the ground.
Would several shorter rods wired together be sufficient?
Burying several meters of copper pipe to mimic the old water main earth?
Export the house earth using suitable cable? Ie perhaps 16mm?
 

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