Not allowed under all circumstances.
Not allowed under all circumstances.
[...]
I wasn't talking about testing an earth rod, I was talking about working out if it was possible to export the house earth rather than having to install a rod.
For which job a loop impedance tester would be extremely useful :-)
Interesting procedure of yours though; I'll hang on to that post.
Hwyl!
M.
If you have PME, it is not permitted to export the house earth. Outbuildings must have their own.
OK folks. Thanks for the advice. The shed (stone outbuilding build into an earth bank) itself was originally very damp indeed. The single socket and light bulb in there used to run form an old wylex board and this was earthed via the steel armour of the 25mm swa running to the shed.
I have since demolished the old shed and rebuilt it to the same dimensions, reusing the old stone to reproduce the outward appearance. Internally its block built with dpm, drainage & insulation pipes to keep it all dry and snug. Because the cable was buried under things I don't want to dig up putting a new cable in or adding a new earth cable was not an option I wanted to use. I was a little worried about using the armour for an earth as I hadn't come across it before. Asking a few electricians came up with some very different answers from what I've read here. I have now decided to use the swa as an earth (only 12m long) but I will be adding shrouds and washers with tags to bolt short lengths of heavy earth cable connected to the earth bars on the CU's at each end. No earth spike. :) Previously at the house end the swa was relying on the brass glands connection via the painted steel consumer box and the bolt holding the earth bar onto the box for the earth path. No attempt at removing paint though. At the shed end the armour had been manipulated so that it occupied several different screw down terminals on the earth bar of the wylex box.
Anyways :) Ta very much
I will of course be ensuring that my Part P capable professionally qualified person will be doing the job right.
Huh?
Sorry, not met that one before. Can you point me in the direction of the appropriate regulation?
Hwyl!
M.
OK. But in my ignorance I'd say exporting the house earth with a suitable cable - even 2000 mm might just work.
I still don't know where Huge has this idea from. I can see how the logic *might* work, but I'm blowed if I can find any reference to it in the regulations or in the OSG.
But it's been less than two days since he posted so I'm going to give him a bit longer to respond :-)
Hwyl!
M.
That is not the case. This is a matter at the designer's discretion, the main criterion being the feasibility of implementing an equipotential zone in the outbuilding in question.
Sorry, perhaps I got a bit lost there, but ISTM that you were talking about "testing the earth" after pointing out to someone that the RCD test button only tests the RCD's internal operation, not the earthing.
Shows the dangers of not being absolutely precise in a text-only forum, eh? The way I read the post it went like this (paraphrased, obviously!):
OP said: I need to install an earth rod.
I said: Have you thought about exporting the house earth?
OP said: You might be right. Could I make the connections and then test it using the RCD test button?
I said: No, you'd need to do the calculations and then test using the proper equipment.
Never mind. I still haven't worked out exactly what sort of SWA (i.e. csa) the OP has for the job, nor what earthing system his house has, so this is all a bit academic really.
Hwyl!
M.
In message , Martin Angove writes
2 cores of multi-stranded copper about 5mm diameter. Spiral strands of steel wire as armour making a cable that is about 25mm diameter total. The house has an earth that is a big yellow and green cable from the earth bar in the CU connected to a strap on earth connector on the main cable coming into the house.
OK - makes sense when you put it that way. I think I've been sampling the group at somewhat less then the Nyquist rate lately...
2-core SWA (to BS 5467), if really 25mm o/d, would be 50mm^2 CSA, which seems a little excessive. Perhaps you're over-stating the o/d a bit (easily done). An accurate o/d measurement with vernier callipers is needed to identify the size - although you may find this embossed on the sheath [1] along with manufacturer's name, year of manufacture, BASEC approval and British Standard number.
TN-S.
[1] Usually in a format like 2 x 16.0 (i.e. no. of cores x CSA in mm^2).
I read the post as 25mm OD over the outer PVC sheath which without taking detail from a cable chart I would have guessed at about 6 to 10 mm^2 conductors, maybe at a maximum 16? Bigger sizes may be involved if shaped conductors are involved.
or was it your alias? ;-)
According to the Pirelli data sheet for 2-core XLPE SWA to BS 5467 the o/d's are as follows:
CSA O/D mm^2 mm
--- ----
1.5 11.5 2.5 12.9 4 14.4 6 15.6 10 16.8 16 19.6 25 20.9 35 23.0 50 25.3 [... continues to 400mm^2, 54.7 mm o/d, beyond most DIY requirements :-)]Shaped conductors come in from (and including) 25mm^2, IIRC.
It may well be excessive. I put the thin in 15 years ago when we moved here as I had a huge drum of it :)
Still have.
and according to my vernier it is 21.9mm . The drum was not new when I got it so it could well be just PVC cable (rather than this thermo setting stuff) According to my maths it must be 16mm csa as the cores are made up of strands that altogether are about 5mm across.
Yes 21.9 mm o/d agrees exactly with a table I've got for 16mm^2 2-core PVC insulated SWA to BS 6346. (And the TLC site is in error for not having updated the dimension after the change to XLPE.)
In which case the armour CSA is 46 mm^2 and the armour resistance at 20 degC is 3.5 milliohm/m. Someone else can do the design calculations this time...
So to summarise what we know so far, the OP has:
TN-S earthing
A metal-cased CU at the house
Device protecting SWA to shed not known (type, rating)
12 meters of 16mm2 SWA.Unknown CU at shed
Unknown circuits at shed end, though implied small loads.
I would have thought that that spec of cable is going to be fine in terms of both loop impedance and voltage drop but I don't have time to work on the details right now :-)
Hwyl!
M.
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