Ducting ??

[confused 2]

Does SWA cable need to be ducted if going underground between house and garage, or can it just be buried???

 

[mapj1]

Normally it can be direct buried if the ground is soft (free of sharp stones that might tear the jacket and cause the steel to rust). If the ground is not nice, or there is a risk of disturbance then either a sand filled trench, or piping ducts may be used. In a domestic setting this is normally all that is required (bury some 'cable below' tape placed so it gets dug up first.....) If it is in soil that is exposed or under a lawn, then 18" /0.5m is a good minimum, much more clearance is needed if the land will be dug or ploughed, less depth can be OK if its under concrete slabs or similar hard standing that you know will never be lifted during the life of the cable.


Pipes are more common on large sites, or where cabling may need re-routing at short notice, particularly for sites like chemical works etc, where the cables, which may be a mix of mains and instrumentation/signalling periodically erupt under man-hole covers for threading -like a giant version of conduit with threading elbows- it is not normally possible to draw in more than a few 10s of metres at a time, even with the landrover winch and quite often the site is laid with covers. 4 or 6" pipes and draw lines in place but no cables.
On such a site woe betide you if you pull your new cable in and don't thread in a new draw cord behind the old one with it, as then nothing else can be drawn into that tube. Though I have seen brave attempts to add a draw cord to an empty pipe with compressed air and running water - the compressed air seemed to work quite well, surprisingly, though very slowly - a rag was tied onto the rope to make a sort of plug come parachute. I suppose given that optic fibre can be blown into ducts 100s of metres long I should not be surprised, but it looked odd.
To the original question, depends on your soil quality - direct burial may well be OK. - if it emerges through concrete slabs a cast in hockey-stick shape of pipe is often used just for the ends, so if it ever needs re-threading it can be done without smashing up the floor slabs.

 

[ban-all-sheds]

No specific requirements for depth of burial are given in the Regulations, except that the depth should be sufficient to prevent any disturbance of the ground reasonably likely to occur during normal use of the premises. Hence, a cable to outbuildings installed under a concrete path could be at 400 mm, whilst if running through a cultivated space which could be subject to double digging would be less likely to disturbance if buried at 700 mm.

Cables must be identified by suitable tape or markers above the cable, so that anyone digging will become aware of the presence of the cable. Cable covers may also offer both identification and protection as shown here:

It is often useful to lay a yellow cable marker tape just below ground level so that this will be exposed by digging before the cable is reached. Careful drawings should also be made to indicate the exact location of buried cables; such drawings will form part of the installation manual .