Adding a further TT Earth Rod to garage

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I have started to review and consider the wiring in my late sixties built house that I have lived in for a few years. The wiring is pvc and not rubber and appears pretty sound but has had various additions before my time ( and a couple since) and no doubt before the 2003 regs as some wires are red and black. There are no issues in terms of functionality and I can see no glaring safety issues but I doubt looking at it some of the practices then are up to scratch now. My intention is to get an electrician in (who recently did a good job on some lighting wiring in my lounge refurbishment) to do some testing to highlight any important improvements which hopefully won't involve a complete rewire as the existing cables appear sound. (I'm more concerned about disruption than cost, to be honest, as it has a concrete floor)
I've given the above information because I really don't want the answer to my question below to be " you shouldn't be doing it mate, get an electrician in" since I will be!
So the power to the garage is taken from a fused ring main circuit that has just two double sockets on it indoors. (Underground for just a metre or so via a metal conduit.) It is connected to a small consumer unit with 32A and 6A for the lights and a 30ma RCD, you know the sort of thing, and the supply to two double sockets and the lights come from that with a further socket and light in an adjoining brick workshop come shed.

So the question is this. The house has what I think is not a brilliant TT earth spike at the front. At least it is in fairly wet clay most of the time but looks like one of the basic 4ft copper plated rods. So I was wondering if it is ok in the meantime to add a further earth rod next to the garage and take that straight to the earth of the garage consumer unit to improve things and know that the garage will have a good earth? (A plug in socket tester shows earth ok on all sockets but I don't know what the resistance is yet).
 
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I suppose it depends on what the resistance of the rod is.
Find out what it is and then think about it, in which case I suppose you will need an electrician or, at least, his meter.

As long as you have 30mA RCD, which you do, it won't make much difference

What is the difference in appearance at the surface of one rod, two or several?
 
The current TT is a single (looks like 3/8") copper plated spike. Probably 4 ft with 4" above ground with a 10mm earth cable from the clamp to the main consumer unit. Not really sure whay you mean by appearance. It looks like a weathered earth rod!
 
The current TT is a single (looks like 3/8") copper plated spike. Probably 4 ft with 4" above ground with a 10mm earth cable from the clamp to the main consumer unit. Not really sure whay you mean by appearance. It looks like a weathered earth rod!
I think what he means is that by looking at the visible part (above ground), you cannot tell by the 'appearance' of that whether what is below ground consists of one rod, or maybe 2 or 3 screwed together.

Kind Regards, John
 
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Thanks, I see. I'm pretty sure it is just the one as it is those relatively cheap thinner ones that are widely sold and not threaded so I think that it is just over 1 metre in the ground. Probably okay in this weather ....... but. I think my concern is that by the time the earth conductor reaches the garage consumer unit it may have a few connections and doesn't look that substantial just being an extension of the old ring main cable, the thought being you're only as good as your weakest point.
 
Thanks, I see. I'm pretty sure it is just the one as it is those relatively cheap thinner ones that are widely sold and not threaded so I think that it is just over 1 metre in the ground.
Fair enough.
Probably okay in this weather ....... but. I think my concern is that by the time the earth conductor reaches the garage consumer unit it may have a few connections and doesn't look that substantial just being an extension of the old ring main cable, the thought being you're only as good as your weakest point.
If you have doubts about the adequacy of your 'main' earth electrode, it would probably be advisable to address that directly (perhaps after testing, ideally after fairly dry weather), rather than adding a further 'remote' earth electrode at your garage.

A lot depends upon the type of soil etc. On clay soil, like I have, it very rarely 'dries out' more than a foot or so below the surface. Hence, my TT rod (which currently probably has a resistance of about 50Ω) rarely rises above 70-75Ω, even after protracted periods of dry weather.

Kind Regards, John
 
The power to the garage is a spur from a ring final circuit with a CU on the end of it, feeding a 32A and 6A circuit? Is the conduit earthed?
 
Thanks John. I think I was being drawn to that conclusion anyway. I am in a belt of very heavy clay which is good (except for gardening!). I have read that a 2 metre 15mm copper pipe would be better than the 4ft plated ones you tend to get in Screwfix etc . I believe people have some success in sinking them by attaching a hose then just "pumping" it down.
The power to the garage is a spur from a ring final circuit with a CU on the end of it, feeding a 32A and 6A circuit? Is the conduit earthed?
It's actually not what I would call conduit. It's something I believe they used in times gone by. It is a fairly thin copper tube (~5mm) which I believe has an inner sort of ceramic insulator. This goes to a metal junction box with a metal gland and the box is earthed so the pipe will be. From there it goes with a short cable to the consumer box. But this is probably my biggest area of concern in that the concrete above it is cracked (not sure how deep the pipe is) but the earth wire in that is all that carries it to the garage, so if that alone broke (it's very old) there would be no earth. I'd assumed that if I put in another earth spike any short would take the path of least resistance to ground which would be either to that one or the existing depending, but if the single earth wire were to be damaged the external circuit would have a backup from the new spike and the external consumer unit. In the long run I will probably get the electrician to put a new external supply to it as I noticed there are spare connections on a Henley block in the Consumer unit but thought this might be a simple interim measure.
 
But this is probably my biggest area of concern in that the concrete above it is cracked (not sure how deep the pipe is) but the earth wire in that is all that carries it to the garage, so if that alone broke (it's very old) there would be no earth.
Ok. you could just run an additional earth wire to a connection in the house.

I'd assumed that if I put in another earth spike any short would take the path of least resistance to ground which would be either to that one or the existing depending,
It doesn't take the path of least resistance but all paths in inverse proportion to their resistances.

but if the single earth wire were to be damaged the external circuit would have a backup from the new spike and the external consumer unit. In the long run I will probably get the electrician to put a new external supply to it as I noticed there are spare connections on a Henley block in the Consumer unit but thought this might be a simple interim measure.
Not the simplest, though.

You really need to establish the effectiveness of the existing rod.
 
Okay. Thanks everyone for your useful and prompt responses.
 
Thanks John. I think I was being drawn to that conclusion anyway. I am in a belt of very heavy clay which is good (except for gardening!). I have read that a 2 metre 15mm copper pipe would be better than the 4ft plated ones you tend to get in Screwfix etc .
Well, 2 metres is obviously 'better' than 4 feet, but the latter is likely to be adequate, particularly since you also have clay soil. If you had very sandy soil, it might be a different matter.

As everyone is telling you, if there are uncertainties in your mind you ought to get the resistance of your earth rod measured.

Kind Regards, John
 
So the power to the garage is taken from a fused ring main circuit that has just two double sockets on it indoors. (Underground for just a metre or so via a metal conduit.) It is connected to a small consumer unit with 32A and 6A for the lights and a 30ma RCD, you know the sort of thing,

So you don't want the CU in the garage then as the circuit is already protected by the 32a of the ring it is taken from. Do you also have another RCD indoors as well? For garage lights a FCU with 5a fuse is all that is needed.
 
So you don't want the CU in the garage then as the circuit is already protected by the 32a of the ring it is taken from. Do you also have another RCD indoors as well? For garage lights a FCU with 5a fuse is all that is needed.
Only the OP can tell us what he "wants". It's undoubtedly true that he doesn't need a CU in his garage, but since he's already got one there is no sensible reason for ripping it out.

Kind Regards, John
 

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