Having just dug a 40 metre long trench for drainage from the house, about
1.5 metres deep, I'm not keen on the idea of digging another. Would it be
madness to use the same trench for sewage, electricity supply to a barn via
40mm conduit and water supply to the barn?
yes. but be careful. You can bed water and sewage down in gravel but
power cable should not be in gravel alone. Better to use sand.
And bear in mind sewers occasionally need digging up. so try and locate
the mains as far as possible away..and tape over it.
Are "drainage" and sewage" one and the same, or do you have separate
systems for surface and foul water? If the latter, it is usual to put
the sewage pipes at the lowest level so that if they leak you don't get
sewage mixing with surface water.
Sorry for the lack of clarity, sewage and surface water are completely
separate. The purpose of the trench was to connect the house to the septic
tank which is near the barn.
Yes, sewage will be the lowest in the trench, but tiday threw a new
problem, the sewage pipe has shrunk by about six inches during the day and
had opened a joint - it's push fit corrugated 6" tube - I've not seen this
before and I can only put it down to the current 40C noon temperature.
Nothing else has changed in the 24h since the drain was laid.
Presumably the pipe expanded with the heat, extending the overall
length. When things cooled down, the joints weren't strong enough to
pull the full length back up a steep slope as you mentioned earlier?
Perhaps the corrugations prevent this happening when the trench is back
What country is this? Your said "no armoured" impying it's not the UK... and
I find a building code that prohibits armoured rather than requiring it to
be very weird.
OTOH for electrics, if you are in the EU, AFAIK you *could* do it to IEE
standards as long as the whole circuit is done that way... of course, a
warning sign on the CU stating the fact would be courteous...
Me? If the drains are going at the bottom of the hole, It's back fill to 1m
deep, then lay the water and electric at that depth either side of the
trench, then backfill 30cm then warning tape, then fill over.
What cable are you "supposed" to use? Does it require ducting?
It's in Italy, where "safety" includes not distinguishing live from
neutral. The electrician is insisting that 40 metres run of cable does not
need to be more than 2.5mm^2. I'm over ruling him on that one. However he
insists that burying armoured cable without conduit is "illegal".
Ah. And that is the case in many EU countries... Even in the UK, neutral is
now termed as a "live" to break the associaion of it being "safe".
What sized supply are you running to the workshop? 2.5mm @40m is going to
have a practical limit of about 8A for a circuit supplying lighting due
primarily to volt drops - but there also remains the question of whether an
MCB or fuse will even clear with a dead short on the load end - or at least
whether it will clear in 40mS (unless we class this as a distribution
circuit and have local MCBs/fuses in the workshop - or RCD protect the
circuit). Sorry - do not have my books to hand right now...
For a 32A W/S supply, I'd be looking at 10mm2 over that sort of distance.
What sort of circuits are you installing and total load?
This is of course IEE 17th numbers - but although the regs may be different,
physics doesn't change a lot between UK and Italy.
One of the other big impacts with be how the earthing is supplied to the
workshop - local earth rod?
I agree... Have a look at http://www.tlc -
It's not perfect - does not allow for different breaker types (B vs C vs D)
but it will be a reasonable rough guide.
I suppose if you have a local bod doing it, he will have to do it to local
regs - but there's no way he can complain about beefing up the spec.
Perhaps their "armoured" is built to a different design than ours and
genuinely not rated for direct burial?
If you don't mind the dosh - bury a couple of flexiducts (sort used for
traffic lights etc - comes in big coils) - one for mains and one for pulling
through all manner of intresting other services and leave a rope in and
maybe 1-2 intermediate small manholes.
That's possible. IIRC, in the USA there is a distinction between the
normal equivalent of PVC twin & earth cable and "UF" (underground
feeder) cable. The former is not supposed to be used underground,
even in conduit; the latter has mould- and mildew-resistant outer
Most sites I could find do seem to concentrate on installtion using
conduit/tubing/mechanical protection methods, but this shows a direct
buried armoured cable (with a marker above)
Might be useful for starting an argument with your sparky!
On Tue, 23 Aug 2011 08:18:47 +0100, Adam Funk wrote:
Yes, I'm not even sure if I'm allowed to use any kind of armo[u]red cable
underground where I am in the US; I can bury 'bare' cable, or I can use
conduit (and I think that conduit has to be 12" deep or more, and 'bare'
wire 24" or more).
On Tue, 23 Aug 2011 15:27:39 +0100, The Natural Philosopher wrote:
No, I don't believe so, at least not with anything that'd survive an
impact with something like a shovel; I suppose they just rely on it being
deep enough to be out of the way in most cases :-) (there is a
requirement to use conduit on the verticals where they enter/leave the
ground, just not for the horizontal sections)
They're very big on calling in location services here before digging,
with good reason :-) The last few times I've done that it's been a quick
form on a website and all the utilities companies show up in a few hours
and use their gadgets to mark out where their services run.
At some point I need to run new wire up to my workshop (so I can have
220V up there rather than 110-only), but I need to look into the rules as
it'd be nice to just have some form of service trench so I can run
network, phone and water up there, too - and add other stuff at a later
date if needed.
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