I am running a supply out to a garage in a courtyard, it's in swa, is it recamend it be laid in a buried tube labelled or just buried without the mechanical protection? Also as the regs says out buildings require their own means of earth, would it be sufficient to leave the earth rod clamp exposed (vulnarable to damage and the local fools) or stick it in a secure enclosure? Thanks for the help guys
Sub main to garage block.
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Firstly, this is notifiable //www.diynot.com/wiki/electrics:part p - legal requirement.
This courtyard - who owns it? You say its a garage block so I assume the block has communal access. Do you have permission to lay this cable? If so do you have insurance in case anything goes wrong? (Dig through another cable/pipe)
How far is it (cable-metres, not walking-metres)?
Where in the regs does it say about they require their own means of earth? If your house supply is TNC-S (PME) then you should be fine exporting the earth from there. If however its TT, you should sink another earth rod at the garage. Rod ends should be in an enclosure, yes.
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See Issue 16 Autumn 2005 wiring matters although outdated it is still very good.
The earth arrangement is complex as it depends on location. For example a garage at end of garden in an estate of houses where all gardens back onto each other would likely be supplied using house earthing arrangement.
However a house on it's own and garage at bottom of garden with countryside beyond then likely a TT earth would be used.
As to protection under fault conditions the voltage on the earth rod could be lethal so they are always protected and provision made so no one can touch the rod or ground to a safe distance away from rod. Distance will vary but if a pre-made assess point is used so rod is sunk to below ground level with inspection lid above then unlikely there will be any problems.
As to using pipes to run cables it is not the rules we consider but cost. If laid under slabs then if there is a fault relativity easy to renew however under tarmac it would destroy the drive so with latter we would use a pipe so it can be renewed without high cost.
As to Part P that would depend where supplied from. If supplied from commercial premises then not required but if from Domestic premises in England and Wales then likely it would require Part P.
Since you say courtyard this may be a farm and there are special rules for farms with cables being buried deeper and far stricter earthing arrangements.
Once you have read the Wiring Matters article you may have further questions. The RCD requirement has changed since the article was written and you are likely to need RCD protection somewhere.
The earth arrangement is complex as it depends on location. For example a garage at end of garden in an estate of houses where all gardens back onto each other would likely be supplied using house earthing arrangement.
However a house on it's own and garage at bottom of garden with countryside beyond then likely a TT earth would be used.
As to protection under fault conditions the voltage on the earth rod could be lethal so they are always protected and provision made so no one can touch the rod or ground to a safe distance away from rod. Distance will vary but if a pre-made assess point is used so rod is sunk to below ground level with inspection lid above then unlikely there will be any problems.
As to using pipes to run cables it is not the rules we consider but cost. If laid under slabs then if there is a fault relativity easy to renew however under tarmac it would destroy the drive so with latter we would use a pipe so it can be renewed without high cost.
As to Part P that would depend where supplied from. If supplied from commercial premises then not required but if from Domestic premises in England and Wales then likely it would require Part P.
Since you say courtyard this may be a farm and there are special rules for farms with cables being buried deeper and far stricter earthing arrangements.
Once you have read the Wiring Matters article you may have further questions. The RCD requirement has changed since the article was written and you are likely to need RCD protection somewhere.
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Run it in some kind of duct (such as soil pipe). this is not for protection (that's what the SWA is for!) but to allow the cable to be replaced or other cables drawn through alongside it. (leave a pull-rope in there for the future.)
You need to give much more info before anyone can advise on the earthing arrangement.
You need to give much more info before anyone can advise on the earthing arrangement.
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I don't quite understand this. The voltage on the rod will be earth potential. Anyone touching it will be stood right next to it. Surely there can't be enough of a potential gradient over 1ft, and the impedance of a metal rod is effectively zero.
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I don't quite understand this. The voltage on the rod will be earth potential. Anyone touching it will be stood right next to it. Surely there can't be enough of a potential gradient over 1ft, and the impedance of a metal rod is effectively zero.
It would of course depend on size of earth rod but if you with a fault connect the earth rod to line then the earth rod and ground right next to it will be at Line voltage. As you move away from the rod the ground will have a gradient and by time you are 50 meters away it will be at neutral potential or there about.
The steepness of the voltage gradient will depend on ground resistance and how wet. If the ground is a very bad conductor the gradient will be gradual but at some point one will reach a point where any animal without shoes could be killed. Dog or Cat and dogs have been killed due to faults under the pavement.
With a boat for example the resistance is more known and a boat in a canal with an earth fault would kill anyone swimming by it. However in the sea because the sea is a better conductor you need to touch the boat before you will be killed.
Two things should protect us. The first is driving in a long stake and covering the top so without a tool no one can touch it. The second is the RCD should trip removing the fault to earth. However we should not rely on a RCD and not guarding the metal work from being touched would be silly.
If the rod is of a very low ohm reading. One I fitted for a Radio Ham was 0.3 ohms being 4 rods each 2.4 meters long and connected together with bear copper strip at 1 foot deep then touching it will not be any real danger. However I have needed to sink 5 rods and more each at 1.2M long to get an 8 ohm reading and earth rods used with a house are often reading 60 odd ohms. Where the water, gas, and other metal work is also bonded the resistance is likely a lot lower but just the rod on it's own it can be accepted at 200 ohm and at that sort of resistance voltages could be high.
Resistance area (for an earth electrode only). The surface area of ground (around an earth electrode) on which a significant voltage gradient may exist.
Simultaneously accessible parts. Conductors or conductive parts which can be touched simultaneously by a person or, in locations specifically intended for them. by livestock.
NOTE: Simultaneously accessible parts may be: live parts. exposed-conductive-parts, extraneous-conductive-parts, protective conductors or earth electrodes.
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