My brother has asked me to look at some wiring in old farm buildings.
I've done wiring in the past and am an electrical / electronics
engineer so know I can do it safely, but I'm not clear about the
requirements for bonding in steel farmed buildings. Reading the regs
suggest that it would be necessary to bond across every bolted joint,
but steel is a pretty good conductor so is it normal to consider the
bolted metal to metal joints are sufficient? One building, a grain
store, has been wired quite recently; it has a separate earth wire to
the local distribution box in addition to the cable armour wired back
to the earth/neutral bonding point, but there is no bonding across
every bolted joint. The building I'm looking at used to be used as a
cattle shed and only needs the lighting refurbishing. I'm tempted to
run a single bond wire to a convenient point and rely on the bolted
steel joints giving a good earth to the remainder. I've also
considered testing to confirm that there is a good earth to all the
What is considered best practice? and if it's different what is the
Jim Backus running OS/2 Warp 3 & 4, Mac OS X and Win98SE
bona fide replies to j <dot> backus <the circle thingy> jita <dot>
I had this issue last year when I was giving up a lease on a building. It
needed a new certificate.
One electrician said that each joint would need bonding, another said that
one would be fine.
I checked that the council's own electricians were happy with this before
having the job done and they were so we went with the latter.
You really should get an electrician experienced with livestock
premises if the building or location is going to have any livestock
present. The danger from earth leakages is much higher than it is
for humans - a leakage which you can't even feel can kill a barn
or field full of livestock all too easily. You need an electrician
who is familiar with designing solutions for livestock situations.
ISTR someone on this newsgroup lost one or more horses this way
in the distant past.
[email address is not usable -- followup in the newsgroup]
On Fri, 12 Mar 2010 11:14:35 GMT someone who may be "Jim Backus"
There is not a simple answer to this simple question.
If there is a reliable metal to metal joint then that is more
effective than any bit of copper cable. For example where copper
pipes are joined by soldered or compression fittings then only
someone paid by the hour and for materials would suggest bonding
across the joints.
So the first question is, is there reliable metal to metal contact?
I have no idea, you will need to decide, possibly with the help of
someone else, which is best done with a meter.
If the answer is yes then the second question is, is this reliable
metal to metal contact likely to remain until the next inspection?
Again not a question I can answer. If rain is getting in, or the use
of the building is likely to cause condensation inside (for example
animals, wet plants) then the answer may be no.
I agree with the point others have made about experienced firms.
This is not something for house wiring bodgers, it is something for
those with experience, probably a well known firm of local
electrical contractors rather then a one man band. That is not to
say that you may not find a one man band who has the relevant
skills, but it is more likely they are in a larger and well
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
BS 5502 barns are bolted together using plated (probably zinc) bolts.
The portal frames are bedded in concrete pads, usually 0.9m cube.
The frame can be galvanised for livestock housing but, more usually
comes with a coat of primer.
Stanchion to rafter and rafter to rafter at ridge generally uses 6 bolts
Some barns use timber purlins but most are Z section galvanised steel
bolted at each rafter. A barn with timber purlins and cement fibre roof
would have no conductive path between frames other than the soil between
None of my barns have any extra strapping.
Fortunately the supply here is provided with an earth. PME might be a
different kettle of fish.
I would strongly advise that you get a good set of local sparkies in.
There are problems with livestock, in that figures of 30v or less have
been known to kill livestock and due to the longer distances between
front and back hooves compared to human feet the risks are even greater.
How much is one or more dead cows worth? I would suggest that you have a
glance at the 17th Ed and see how much has been written on this and also
do you have all the kit, such as earth rod resistance checks?
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