I am in the process of having a large 'shed' installed to act as a
small workshop and study which naturally needs power. The total load
including electric heaters is around 24A but certainly shouldn't
Now I intend to lay an underground cable in due course, but this will
require a small digger (solid clay around here) and I have no way of
gaining access to my property with one. At least not until the council
fill in the 4ft deep 8ft wide trench behind my property where they are
culverting a small brook.
A temporary solution would appear to be to suspend the cables. The
distance is only 20m so shouldn't present any major problems, but are
there any regulations I should be aware of before dangling cables
between my house and the outbuilding?
Before anyone suggests bunging the digger operator working on the
council job some cash they're already long gone...
This is going to cause problems with a span of 20 mtrs. I'd personally take
the power supply under ground where ever possible over that sort of
distance. You'll find that straining forces will be absolutely enormous to
be able to hold anything up and away to a safe working height for a mains
electrical supply, and you'll need at least posts between the gap to take up
There is no specific instruction in "the regs" as far as I can see, but
table 4B (p104) in the On Site Guide is very relevant...
For a PVC cable "supported by a catenary wire" there is "no limit" on
the maximum length of span. Non-supported PVC gets just 3m.
At road crossings there must be 5.8m miminum height (obviously taking
any sag into account), at other positions "accessible to vehicular
traffic" 5.2m, in positions inaccessible to vehicular traffic (except in
agricultural premises) 3.5m - just to keep it out of reach one assumes.
For a temporary installation I wouldn't worry about the effect of UV on
PVC cables, but if it's to be for 5 years or more it may be worthwhile
investigating a cable that isn't susceptible to UV deterioration.
Martin Angove: http://www.tridwr.demon.co.uk /
Don't fight technology, live with it: http://www.livtech.co.uk /
I lost my copy of the overhead line regulations when we moved some time ago
but this post reminded me of the "good old days" when hard drawn copper
strung between D-irons and porcelain insulators was the norm for overhead
services. Somewhere in a shed I believe I have an old linesmans tensioning
I watched the tensioning of the replacement 250,000V lines over
our industrial estate. The 'tensioning device' was a winch truck
same size/shape as one of the airplane tugs but with a winch built
in, and anchored with about half a dozen large skips full of rubble
to stop it being dragged along the ground.
The full Regs have an extensive section on temporary supplies for
construction sites, according to Steward & Stubbs "Modern Wiring
Practice" which says it's section 604. It's possible there'd be a
minimum recommended height, but the "obvious" answer is "out of the
way of likely traffic" and "adequately protected against mechanical
damage". Said Section also apparently has plenty to say about
disconnection times, use of ELV (extra-low-voltage) supplies, and the
like. Using that section of the Regs as a model would be a pretty
gold-plated demonstration of adherence to Good Practice, but might
be non-sensibly expensive.
In my utterly unqualified opinion, it boils down to "how temporary is
temporary", and on the actual risks of mechanical damage. At one
extreme, let's say you'll be putting in a permanent SWA cable in a
trench in 2-3 months time; and no-one but you and immediate family
members use the space between you and the outbuilding; and that you'll
only want power in the outbuilding a couple of times a week. In that
case (and with a vague memory of you saying the max load for now is
twenty-something amps, yes?), it would not be unreasonable to string
a 2.5mmsq blue arctic cable (or similar) along a more or less out
of the way route - along a fence - and have it disconnected most of
At the other extreme, if you have public access between
house and outbuilding, and/or employees/contractors working for you
in the outbuilding, you shouldn't be contemplating any kind of
shortcut: if you can't trench for now, running SWA along the ground
covered in (expensive) road-traffic-duty cable protectors (like a
small speed bump) is the very minimum you could try getting away with
- and even then I wouldn't want to think about the liability; the
Electricity At Work laws kick in at this end of the scale.
Somewhere inbetween (basically your own private land, but with limited
access for visitors and people doing jobs for you, to whom you owe a
duty of care) you might string some 2.5mmsq or larger HiTuf up along
some poles at least, oh, 8 ft overhead, or secured to any boundary
wall/fence you might have for most of the distance. (HiTuf is notably
lighter for rigging up high than SWA would be, and though you're
supposed to use separately earthed metal catenary wire for a
permanent suspended installation, with supports every couple of
yards it'd be adequately self-supporting, and too stiff to sway in
the wind, though aesthetically naff. If you do have walls or fences
to secure to for most of the run, and negligible access to the run,
you could use the SWA you're going to bury, temporarily fixed up.
For a permanent install, HiTuf or SWA attached to walls is OK, but
not to fences which wobble and maybe blow down...)
Hope that suggests some options... Stefek
From memory, it would limit you to 110V appliances too, for all
appliances less than (IIRC) 4kW (although I have heard a rumour
that EU law has now overriden this restriction;-)
Cable heights are in the On-Site Guide, and depend if the area crossed
is just pedestrian access, vehicle access, or public highway (again
from memory -- don't have either regs or OSG on me at the moment).
However, these are just guidelines, and may not be suitable in all
"Jason Arthurs" wrote
| Now I intend to lay an underground cable in due course, but this will
| require a small digger (solid clay around here) and I have no way of
| gaining access to my property with one. At least not until the council
| fill in the 4ft deep 8ft wide trench behind my property where they are
| culverting a small brook.
You don't have any military pals who could lend you a temporary bridge?
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.