I'm after getting power to my seperate garage, and I have two options: Run a cable around 30 odd meters of garden wall until it gets to the garage, or go underneath 3 meters or so of lawn. Either way, it's going to be exposed to the elements and anything that might be living there, so I'm presuming armoured cable is a must. I'd rather go underground, but I have no idea what is required to do so.
Are there any regulations that specify how deep a cable must be buried? Also, presumably it's a requirement to have that "Warning, you're about to dig through a bloody big cable" tape over it - is there a requirement for a certain amount of space between cable and tape?
Also, I really don't fancy digging up and reconcreting the garage or kitchen floors, so the cable will be leaving the house and entering the garage through the wall. I'm thinking steel conduit attached to the wall for the full vertical journey of the cable - is that the right approach?
I'm not qualified, so these are snippets, some of which may need double checking in the details... Don't take this as authoritative, just things that you may need to research more...
Recommend you read this first - a lot of wisdom from pe> I'm after getting power to my seperate garage, and I have two options:
Yes, armoured - known as SWA. Other protected cables are potentially OK (eg MICC) but SWA is the easiest for the job. Make sure you know how to handle the earthing of the armour via the gland kits - it is essential.
I thought there used to be specifics, but it may have disappeared (in specifics) from the current regs. What you are aiming for, in spirit, is deep enough to reasonably avoid damage. How far down would someone be reasonably digging a flower bed? Go deeper. 2ft at least IIRC might have been a recommended depth once upon a time. And/or protect it with some concrete capping. Lawn is less bad - but you want it deeper than the prongs of a fork can go. As it's only 3 meters, capping will give it best protection at minimal effort/cost - but it's not essential.
Yellow tape, made for the job - even B&Q sell this.
This is some:
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you should ideally prepare the ground - take out any stones from the trench, and put a layer of sieved soil or soft sand under and over the cable before infilling. Don't know about the specifics of the depth of the tape.
You can clip the SWA to the wall and take it in a hole. Watch the bend radius isn't too tight. No need for conduit - SWA is protected cable.
Except the bit where it goes through the house wall. Is it a cavity wall? PVC needs protecting from some types of cavity insulation which are now known to eat PVC over a long period of time.
Earthing - complex area. What type of earthing has your house got? PME, TT, etc?
This makes a big difference to whether you will export the house's earth to the garage or use a local TT system (earth rod). If latter, you need to design in a time delayed RCD too. Is the garage a metal affair or brick/concrete?
How much current are you supplying - do you know how to correctly size the cable? Will there be a mini consumer unit in the garage, or something simpler like an FCU for the lights? Will the supply for the cable be coming off the house CU or an FCU?
Hope some of this helps - more informed people will undoubtedly comment soon :)
The regs do not specify a buried depth but say that the cable should be deep enough to avoid damage from all reasonably expected occurences. However, the electricians guide suggests 700mm. The cable should also be laid in sand to prevent penetration by stones The thickness of sand isn't specified but 75 - 100mm should be the minimum. Warning tape should be laid above the cable. This should be deep enough not to be exposed during normal digging but far enough above the cable to give adequate warning. I would put it at 500mm. You should also make accurate drawings of the cable route. Do remember that you may have a lawn over the cable so damage is unlikely but futeure house owners may use the area differently.
on abit of a generalisation, most people, when they see a change in composition as they are digging start to dig more carefully, so if this holds true, dig a comfortably deep trench, as deep as you can(sensibly) then use sand to 'bed' the cable then chuck some limestone over that, couple of 100mm then infill with soil and all the other gubbins mentioned. that should make it obvious to any one that something is there!
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