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Posted: Sun Feb 01, 2009 8:47 pm
by zajonc
I am digging a trench to lay an armoured cable to go to my new greenhouse. I have been told that I should dig the trench alongside the fence because then the cable is out of the way and unlikely to be disturbed. I have been given advice on how deep to dig the trench - figures range from 30 cm to 50 cm. I have no problem digging the trench to any reasonable depth - the soil is sandy and easy to dig. My question is: am I endangering my fence? The fence has concrete posts with slots in. Standard fence panels are slotted in between the posts. In between the soil and the fence panels there are low concrete panels. The fence is of very sturdy construction and has shown no inclination to fall down so far. I don't know how deep the posts are, but they are neatly encased in what looks like a mixture of concrete and gravel. The fence is exposed on my side because I have removed nearly all the plants, but on my neighbour's side (the east) there are plenty of shrubs and trees. I own the fence. The cable will be laid in about three weeks' time. The trench is eight fence panels long (about 16m). So far I have dug to about 30 cm and I would like to dig deeper, but I am worried. Thank you for any advice you can give me.
Helen
Posted: Sun Feb 01, 2009 8:57 pm
by msh paving
dont got to close to the fence, 2ft away,450-500mm is deep enough, dont backfill stony material ontop off cable,be a good idea to lay marker tape over cable about 100mm from top off cable so you know its there before you hit it, 
Posted: Sun Feb 01, 2009 10:07 pm
by Dave_L
Indeed - bury at as far away from said fenceposts as you possible and DO lay a marker tape above it.
Posted: Sun Feb 01, 2009 11:44 pm
by lutonlagerlout
dont want to be a killjoy here but why cant the armour cable be clipped to the fence or fence posts,that way theres no danger of people not seeing it
LLL
Posted: Mon Feb 02, 2009 11:39 am
by Tony McC
And why not use a duct to make replacing or adding cables that much simpler?
If you use a duct, you need go only 200mm deep and keep the trench to just 80mm or so in width. This will minimise any risk to the fence posts. If you use a 40mm duct, it would then have at least 150mm of cover and as Dave_L suggested, it's ALWAYS a good idea to use a marker tape just in case the next person to dig there is not yourself.
Posted: Mon Feb 02, 2009 1:55 pm
by zajonc
Thank you very much to all the kind people who replied to my question. My fence is now buried under snow so there is no danger at the moment (only joking - but the trench is filling up!)
I don't want to move the trench to 2 ft away from the fence because I have a couple of mature shrubs there that I don't want to lose. I would, of course, give the plans of the cable to whoever I sold my house to, and since the garden is quite small and the greenhouse will have plug points in it, I am hoping that anyone digging in the garden will be able to deduce that there must be a cable somewhere between the fusebox and the greenhouse (which are both on the same side of the plot).
I hadn't thought of attaching the cable to the fence, so thanks for that suggestion. I'm not that keen because I wouldn't like looking at the cable, so then I would probably cover it with plants, and then I might nick it when pruning the plants (I don't know whether SWA cable is a match for a pair of secateurs or not). Also, if the fence does blow down despite me not half-digging it up, or gets damaged by my neighbour's ivy, that could damage the cable.
My plan was to tip a bit of builder's sand over the cable, backfill the hole a bit, and then a little higher up, put a layer of gravel and spray paint it red. This is my dad's idea. It would be much easier than putting a layer of paving stones over it, as my book suggests. However, tape would certainly be easier and cheaper, and I can get it from B&Q, according to their website.
But - I really like the idea of ducting! Sounds like it's cheap and easy to use. But where can I get it? I don't suppose B&Q sell it. What about Wickes? If anyone knows of anywhere in North Hampshire I'd be grateful for that information.
Posted: Mon Feb 02, 2009 2:35 pm
by msh paving
B+Q or Wicks will sell stuff you can use,40mm plastic waste pipe will be fine and its cheap,they may have duct instock but if not waste will be fine,spraying gravel red is a bit over the top, ducting is way the forward as resident expert says quicker and less digging
Posted: Mon Feb 02, 2009 3:56 pm
by zajonc
Ah, I need to do the digging now the recession means I can't afford gym fees! But seriously, thanks for the advice about the duct. I will go to B&Q or Wickes when it stops snowing and see if I can find some nice waste pipe.
Posted: Mon Feb 02, 2009 4:01 pm
by seanandruby
i think you will find that electric duct must be what it says on the label ie, for electric use. its to do with fire resistence times etc. that armour cable can take a fair old wack with a shovel, it would be a pick that would do the damage. on a lot of our contracts we are'nt allowed to use picks when looking for buried cables. you can always put an electric cables below and distance sign on the fence. sand and marker tape are a must. you could probably beg for tape and duct off a local site.
Posted: Mon Feb 02, 2009 4:32 pm
by msh paving
wicks and b+q wont sell marked electric duct,jewsons have a national contract to supply it for mains service , travis perkins duct is not allowed for service cable, but for a greenhouse supply its fine
Posted: Mon Feb 02, 2009 4:35 pm
by zajonc
Just to clarify - are you saying that if I use waste pipe ducting there could be a fire risk? I can't imagine how a fire would really get going properly under all that soil. And do I need sand inside the ducting or outside it, or instead of it?
That's a good idea to put a sign on the fence - that's foolproof, and doesn't have to look unsightly - I could design and laminate my own!
Posted: Mon Feb 02, 2009 4:51 pm
by msh paving
there no worry of a fire,its only a risk with big cable in small duct feeding whole towns,you little bit is no problem no need to sand inside.....just a sand cover to bed it nice and firm,then cable marker tape over it will be fine,
Posted: Mon Feb 02, 2009 5:38 pm
by Dave_L
This is the sort of ducting that I'd use - making sure it has the draw cord attached, complete.
[url=http://cgi.ebay.co.uk/Electric-Cable-Du ... QQptZUK_BO
I_Materials_Supplies_Electrical_ET?hash=item220354080662&_trksid=p3286.c0.m14&_trkparms=72%3A1688%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318]26 Metres of duct on ebay[/url]
Covered with 75mm sand and then a marker tape on top before backfill.
Again, [url=http://cgi.ebay.co.uk/HAZARD-WARNING-TA ... iewItemQQp
tZUK_BOI_ProtectiveGear_RL?hash=item350158395537&_trksid=p3286.c0.m14&_trkparms=72%3A1683%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318]Electric Cable Marker Tape on ebay[/url] - otherwise it migth be worth asking a local site for 30m or so 