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glenn k
18th December 2013, 02:17 PM
I was going to mill some red iron bark for posts 100x100 or 90x90. I saw on "countrywide" before "landline" that iron bark could be used for insulators, that is electric wires straight to post as they don't conduct. I heard elsewhere (can't remember where) that this insulating property was due to density of the wood and that sugar gum may do the same. Does anyone know anything about this? And would 90x90 posts be strong enough? I thought they would be stronger than round treated pine posts.

Timless Timber
18th December 2013, 02:50 PM
It all depends.

Wood is made from cellulose fiber which is almost entirely composed of water and carbon - which make reasonably good conductors for example when wet.

Having farmed and fought fires for a couple decades I find myself wondering why you would run the fire risk of an electric fence thru timber posts?

Surely running the hot wire on offset insulators makes more sense?

Electric fences (poorly constructed ones especially) tend to start fires.... once things dry out.

And it's NOT just from the fence power supply unit - in thunderstorms in summer - its not uncommon for a fence to be hit by lightning.

If you have long dry grass (e.g. wild oats) and the rain moistened stems blow over in the wind and touch the hot wire - the arcing path to earth created, drys the stems and they catch fire pretty easily.

I thought electric fences thru timber posts was something from the last millennium...

I guess if costs an issue - (and when isn't it living on the land) and you have access to timber posts.... then sure use them - but again if it were me I'd be inclined to run the hot wire on an offset insulator from the post.

Depending what livestock your trying to keep in or what wildlife your trying to keep out might determine the layout for your fence and earth wires / hot wire/s.

Often species like cattle and horses tend to 'push' fences over, trying to reach over and graze grass (or trees even) outside the fence line, so the offset hot wire tends to tickle them up a bit and keep them away from the actual fence post structure and helps resist this pushing trend.

Everyone seems to have their own ideas about what makes a good fence.... timber posts are prone to burning in a fire situation and termite attack (dependent upon species).

There's a lot to be said for all steel fences... do it once and do it right... or spend a lot of time chasing problems with fences, instead of doing other farm work.

Thankfully I'm now retired from farming.

Farms and boats - best days of your life when you buy them and sell them. :wink:

As always others mileage may vary.

glenn k
18th December 2013, 10:44 PM
Thank you for your comments. I was not aware of electric fences starting fires but could see how it would be possible. I am unsure of why an electric fence is more of a danger being hit by lightning than a normal wire fence, also why an electric fence on wooden posts is more prone to start fires as the posts don't conduct. I was wondering whether to have a six strand electric /earthed fence or sheep or pig netting with barb on top.
Cellulose is made of chains of glucose so there is no reason why it should conduct but other resins in wood could conduct when wet. Iron bark does not conduct even when wet and google has not helped to find out about other woods.

Timless Timber
19th December 2013, 02:58 AM
An electric fence is at no more risk of being hit by lightening than any other.

BUT

If you run your hot wire/s thru the timber posts tho - should the fence be hit by lightning - then the thin fencing wires carrying amounts of current they aren't designed to do - could start fire/s at each post/s where the resistance creates heat inside the timber post where the hot wire runs thru the timber post.

Simply put timber is flammable.

With respect to carbon... in timber.

Forests are carbon sinks... timber is composed of carbon. I suggest a little research on the process of photosynthesis.

Timber is not a great conductor. It's also not the greatest insulator. It's actually a poor form of semi conductor - because of it's carbon content.

Traditionally power supply companys use timber lamp posts and timber cross arms with insulators on them to convey current. Even then - when they get wet - and they are covered in dust and salt (from the air) they can and do conduct and the current starts pole top fires - often in the timber cross arms.

Power co's don't drill a hole and run the power wires thru the timber cross arms - due to the risk of fire. They use the insulator to try and prevent this electrical leakage and fire risk.

This is principally why I suggest that its probably not a good idea to run the hot wires thru the posts.

When i first bought my farm - it had Jarrah fence posts - with holes bored thru and the hot wires run thru the posts BUT they had inserted 1/2 inch black poly water pipe inside each post hole to try and create an insulator to keep the hot wire away from the wood.

This didn't work out all that well, because the cattle had pushed on the fences and the plastic lengths of poly pipe had slid OUT of the posts and along the wires over a period of time - meaning hot wires were in direct contact with the posts.

We got some summer thunderstorm weather - & I had long dry grass (wild oats) near some of the timber strainer sets - and the moisture in the air and on the posts and grass etc - it started a grass paddock fire.

Luckily we were home and managed to put it out before it got out of our place and into the neighbors.

Whenever there was moisture in the air - you'd hear the earthing of hot wires via long grass stems against the hot wires, or where they arced against the timber post where the poly pipe insulators had slid out of the post and along the wire - or onto a tree branch from outside the property (verge) that would sag with rain wen wet and touch the hot wires.

I knew the place was full of such electrical faults when we first bought it - because in any sort of moist air - the click click click of the electric fence unit as it earthed via the poor setup around the perimeter of the farm caused the TV screen to get a line across it..with each click.

Likewise any time you touched a steel gate to open it - you'd get the odd stray current kick.

I spent ages chasing my tail trying to find and rectify faults, but in the end gave up and stripped out the entire electric fence setup, and all the timber posts, and went to all steel fencing. Never had a fence problem for 20 years after that and no more fires either.

Bad electric fences are a PIA on the farm.

Good ones work well.

All the best ones I've ever come across used steel posts but offset insulators so the hot wire is about 1 foot inside the fence line... on its offset insulators.

Spraying your fence lines early so the long grass (wild oats) never gets a chance to grow up near the hot wires is a great way to avoid most of the potential problems. Often this means grass growing on someone else's land (verges etc that usually are vested in the local shire etc), coz while you can control what happens on your own property its not as easy when the fence is a dividing fence between you and a neighbor or a local govt authority - who never do any maintenance on their side of the fence.

As far as certain timbers being non conductors... regardless of species, I am sorry but its a bit of an old wives tail - add a little dust, some light moisture and enough current (lightening strike for e.g.) and if that hot wire runs thru the post (and the holes full of crop dust, spider webs and all manner of other flammable tinder type materials & it will catch fire.

Problem with fires is they can turn into Ash Wednesday type events in bad conditions... and if it started in your place.... and gets into someone else's place - their insurer will sue yours etc etc & its heaps worse when someone dies and the coroner starts poking around to see who's to blame.

Its best to try and avoid shortcuts that can cost you your farm if it's later proven you could reasonably have taken steps to have prevented the tragedy - there's even a possibility of negligent homicide if it turns out an expert witness (electrical engineer / arson investigator) in court presents evidence that running the hot wire thru timber posts was bad electrical design and the root cause of the tragedy.

Its a method that was once common - maybe 30+ years ago when electric fences first came out... everyone in the bush trys to use what you have and save a dollar on the land....

With fires - its best not to take any shortcuts... we are becoming more and more a litigious society like the USA.

Electric fences are a cheap way of keeping live stock in - (or wildlife out) BUT they do have their downsides - in being great ignition sources for fires if not well designed and installed and maintained and when you do get bad weather and the power goes out, wind blows and trees shed their branches etc, a non functioning electric fence won't keep much in or out (so if your stocks out of the paddock and one the road and the local school bus hits it/them and 20 kids are killed - you better believe your in for a world of hurt!.

The whole fencing thing - well everyone has their own ideas of what works and what doesn't.

Maybe speak with a few of the "old timers" locals and see what they use & how they do it. They have probably developed their own system in response to local conditions - their experience could be totally different to mine here on the other side of this pizza.

I just know I bought a farm once with timber posts and hot wires run thru them and it was a dogs breakfast of faults and shorts to earth that caused no end of grief until I eventually got rid of the lot & went new steel.

Whenever their was a serious fault, it was invariably dark, wet, raining, & blowing 10 batsurds outside and I'd sooner have not been out there trying to fix it.

They never go wrong on a nice sunny day when you've got nothing better to do.

They ALWAYS go wrong when your under the hammer or in ya jammies in the wee hours & its bucketing down outside.

You can tell I'm not a great fan of electric fences, and bad ones are just a nightmare.

Others mileage of course may vary.

Cheers

Vernonv
19th December 2013, 02:08 PM
... also why an electric fence on wooden posts is more prone to start fires as the posts don't conduct.I reckon that is pure conjecture and speculation.


I was wondering whether to have a six strand electric /earthed fence or sheep or pig netting with barb on top.Depends on the stock type. For sheep/goats/small stock I prefer non electric i.e. hinge lock/hinge joint. For cattle/horses I'd go one strand (maybe 2 if you run cows and calves) electric and the rest plain.

glenn k
19th December 2013, 03:05 PM
i just spoke to a retired forester and farmer who said he had tables for different woods conductivity but said they all conduct when they are wet, some more than others. He said out in the mulga you could get away with out insulators but not here as it rains too much.
It was over 30 years ago when I heard about non-insulated electric fences and I have not been rural since so I am behind the times no doubt.
I have just bought the place and my fences are not good cattle where getting into the house garden and neighbours places before I got it. I was looking for a cheap way to get new fences as they are beyond fixing. I will look around and chat to locals as suggested thanks very much for the replies.

I will probably still mill some iron bark and sugar gum for posts, and perhaps droppers if I use straight wires, but what sizes would you recommend? I was thinking 90x90 for posts as the timber should be F27 compared with treated pine that may not make F5 though they are larger and perhaps more fire resistant.

Vernonv
20th December 2013, 11:24 AM
I have seen thin lengths of poly pipe inserted into timber posts as an insulators. Seemed to work quite well.

EDIT : the poly pipe extends at least 50 to 100mm out either side.

chuck1
31st December 2013, 09:42 AM
hi Glenn in regards to size our Farm had split posts and they lasted very well 50 years they were local hardwood on southern highland nsw, split post will outlast sawn, sawn will outlast dressed Timber. corner posts and gate post are kept in the round with bark stripped off (300 to 400 diameter.
alot of hard work goes into making split posts with wedges, since replacing posts I turn lamps out of the old ones.
to my knowledge the hardwood had no treatment. we ran 4 plain Wires 10 gauge with with square sheep mesh and 1 top wire of barbwireon top ; with another abit below on boundary fences.
it keeps the 600kg bullocks in with out electric fence we also have plenty of feed for them at the moment

chuck1
31st December 2013, 09:47 AM
size of split post was 150 to 200 by 100 by 100, it varied due to wedging the A's they followed the split down the trunk I assume!