House electrical earth revisited

[JohnRoss]

Following my recent post on "House earth test" I have dug around outside and found the electrical earth wire where it comes out of the building. It has the usual colour insulation for the first 50 cms and then is bare wire which runs below ground under the fosse feed pipes. That side of the house is pretty dry always being very sheltered. The wire is a stiff multi strand and fairly heavy duty.

With the earth impedance reading, using the three probe method, of 266 ohms that I reported last time you can see that I need to get this down below 100 ohms which my experiment using a copper covered earth stake showed that this would do it. My question is can I splice the earth stake wire, bare multistrand earthing wire as was suggested, to the existing earth wire below ground level. I could either clamp this or solder it to the existing wire though no doubt such a connection would need some protection. I think it might be important not to break the existing earth wire when making this connection as some sites have suggested. I could then run the bare earth stake wire along the wall line below ground and connect it to the stake placed in a more exposed and hopefully damper location. It would be possible to connect the new wire to the bottom of the earth link borne inside the building but I would like to avoid this if possible as the walls are rather thick and that would be a rather big job as if digging a trench for the wire in compacted gravel ain't enough! The stake would be in soil by the way.

I note that some some sites recommend that earth stakes with a brass cable clamp have the clamp above and not below ground level so I will have to find somewhere where it will not get mowed! Does this approach sound o.k. or is any of it against French regs? I assume all joints would need protecting against corrosion in some way, grease, paint, tape, potted? Any advice given would be most gratefully received...............................JR

[Gluestick]

Something I'm about to do JR.

And I plan to use a concrete Regard Béton as a receiver for the top of the earth spike and clamp and junction with the 25 m.m. multi-stranded earthing wire: and once done, fill the Regard with a tube of plain silicon sealer. And thereafter whack the concrete tampon de visite on top!

Most heavy duty external hazardous environment junctions (e.g.s RF towers, marine stuff; oil rigs) have used silicon to seal junctions boxes etc against weather for many years: and this is my habit now, for any external junction.

Right or wrong, the multi-stranded will then be carried in red gaine right up to the house wall.

 

[JohnRoss]

Interesting. When you say 25mm (squared?) I take that refers to a 6mm diameter wire. Someone said in another place that the earth wire could be buried bare and not in gaine as this would increase contact with earth which makes sense as long as it does not rot which the person that proposed it said it would not and it was sold sans insulation for that reason. I had thought to solder the new wire to the old so as not to cut the old earth wire and maybe pot the junction in a plastic box filled with silicon rubber. As this would be below ground it would not be visible but would like to stick to what ever the regs say if possible...............................JR

PS I suppose the concrete box like Regard Béton might solve my mowing problem if the top was flush with the surface, does it have a lid? Oh I see that the one that Bricomarché do does have a lid but is not 22cms by 22cms a bit big for the job?

[Anton Redman II]

At the risk on being pedant of the month silicone needs the 'e'.

[Gluestick]

Quite right too, Anton: slip of the finger.

[:)]

[Gluestick]

[quote user="JohnRoss"]

Interesting. When you say 25mm (squared?) I take that refers to a 6mm diameter wire. Someone said in another place that the earth wire could be buried bare and not in gaine as this would increase contact with earth which makes sense as long as it does not rot which the person that proposed it said it would not and it was sold sans insulation for that reason. I had thought to solder the new wire to the old so as not to cut the old earth wire and maybe pot the junction in a plastic box filled with silicon rubber. As this would be below ground it would not be visible but would like to stick to what ever the regs say if possible...............................JR

PS I suppose the concrete box like Regard Béton might solve my mowing problem if the top was flush with the surface, does it have a lid? Oh I see that the one that Bricomarché do does have a lid but is not 22cms by 22cms a bit big for the job?

[/quote]

Copper corrodes very rapidly, JR: also depends on the soil constituents; and personally, I'm putting mine in gaine for this very reason!

If the 1.5 M rod in a very damp place (The plot undulates from back to front and the house is raised well above the road level and the natural water flow is considerable) aint sufficient to produce the desired reading, then we'll simply have two rods!

Yes, the regard is big; but cheaper than the pvc equivalent: also, I'm using it as a junction for other external lighting circuits, as it will be a convenient point to route all wiring into the property.

If I can find a smaller robust item, then I would use that instead.

 

[Chancer]

The local fix for a waterproof cover on an exposed  piquet de terre for a Consuel inspection is a plastic vending cup, proper solutions like mine and Gluesticks just get a smily knowing look from the inspector.

[JohnRoss]

Point taken though the existing earth wire is bare and has not yet corroded through our soil conditions may be different to yours. Someone has suggested using a length of 100mm plastic pipe with an end stop as a removable lid and slot cut for the wire over the top of the stake in the earth pit. I suspect a plastic cup would serve the same purpose just as well!.................................JR

PS What think you of connecting the new wire to the old below ground, solder?

[Gluestick]

Now whilst I do love solder JR ([:)]) on this occasion I think I would elect for a solid copper clamp: simpy because underground there are loads of differing salts and moisture: and you could well suffer from Bi-Metal Corrosion, caused by the electolytic action. Note copper clamp: not brass since this also would suffer from De-Zincification.

Interesting stuff here!

http://www.discount-electrical.co.uk/product.php/861498/black-lightweight-inspection-earth-pit-1-8kg

Better than a beverage cup methinks!

[:D]

[JohnRoss]

Well made for the job I guess. Ok on the clamp so will I see these in the average brico place? I take it that they are smaller than rod clamps........................JR

[Gluestick]

Might be something you have to semi-fabricate, JR: mainly since you wish to connect into the existing earth loop without actually cutting it: and most earth rod type junction connectors I've seen are made from brass.

Thus it must clamp the new feed firmly: and additionally clamp around the existing multi-strand copper.

 

[JohnRoss]

Hi again and yes point about the clamping taken but having compared the existing earth wire with the 25mm² stuff I bought yesterday then I have come to the conclusion that the existing earth wire maybe just stripped heavy duty wire normally used in the house and significantly smaller than the 25mm² wire. I suppose standards may have changed since 1985 when the house was rewired. I have changed my plan and will replace the existing wire where it connects to the earth link in the house with the new wire and maybe splice the old wire onto the new  in the wall cavity without cutting either. On the subject of putting your earth wire in gaine to go to the stake would it be advisable to either grease or oil the wire to limit corrosion do you think? There would be a lot of air, damp air maybe, around the wire in the gaine. Obviously you would not do this if you were just going to bury it without gain................................................JR

[Gluestick]

If the gaine is not cracked or pierced along its length and each end sealed with silicone, then it should prevent ingress of moisture until the plastic degrades: which, considering it is not being irradiated by UV, should be many years.

All provided a gardener doesn't stick a fork tang into it! [:)]

One could always squirt a can of WD40 into the gaine before sealing each end, I suppose: or even pump in Waxoyl.

http://www.waxoylrustproofing.co.uk/waxoyl-rustproofing.php

Or treat it like an automotive battery terminal and coat with Petroleum Jelly.??

[JohnRoss]

Yes indeed and I hope to remember where it is so I don't stick a fork through it. Got the earth stake in the ground and dug the trench with the earth wire in gaine such as you described. Have yet to make a hole in the house wall to pass the wire through and connect to the bottom of the earth link. However did do the three electrode impedance test as described in the helpful article you were kind enough to let me have the URL for in my post about House Earth. The impedance came out at 215 ohms so not good enough yet. Once  I have the wire connected to the bottom of the earth link I will splice in the existing earth wire and repeat the test. If still not below 100 ohms I will get another earth stake and link it into the first one some distance away.

I did do one other measurement which gave very similar result. I wired a 25 watt soldering iron between Live and the new earth and measured the current. I had previously noted the supply voltage between Live and  the original house earth and when the iron was connected I measured the voltage across the iron. The difference between the two voltages must be that lost across the new earth  impedance or thereabouts. Using this figure and the current flowing through the iron and the earth stake the impedance calculated came out almost the same as the three electrode method, interesting!.........................ATB....................JR

PS Got the two earths connected up today and impedance measures 45.5 ohms so I am happy with that though will measure it again once the soil has dried out a bit as is a bit damp just now.........................JR