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?
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?
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:
And probably not much good either IME.
"Ufer grounds" are used in the USA (Google for the phrase) but they don't seem common over here.
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.
In message , BigWallop writes
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.
Dig a pond and throw the wire in ?
In message , Mike writes
:)
I'd have to line it, how conductive is butyl?
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-(
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)
Sounds like a very handy kit. Where can I obtain them? :-)
In message , BigWallop writes
Ebay ? :-)
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!!!!
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.
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).
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.
In message , Martin Angove writes
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?
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?
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.
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.
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: ] 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.
Export the house earth using suitable cable? Ie perhaps 16mm?
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