- #1
webdude
- 5
- 0
G'Day guys,
We have been looking around and feel this would be an appropriate forum full of good knowledgeable people to ask a few challenging questions.
The missus an I are about to build a house on a mountain top that is the highest peak for at least 1-2 km's (1 mile or more). Obviously because of the position we will need to take lightning protection very seriously and I feel we should probably get this done before we even start on the house. Also I tend to 5x over-engineer things just to be sure, and using second-hand industrial waste (cheap) wherever possible.
The mountain is covered in trees, dense in some places and spaced out in other parts. On the very top is a small, cleared, flat plateau of about 30-40 meters (32-43 yards) diameter. We will take down most of the small bushy trees near the top to open up the view, but we have decided to keep a circle of the biggest & tallest trees around the top edge to keep some shade and to help obscure the house into the skyline. Without the small trees, the occasional big trunks won't block our views too much. I believe that as long as these big trees all remain higher than the house (which will be roughly in the center of the flat plateau), they should help with some degree of lightning protection.
The house is likely to be constructed primarily of a heavy gauge steel frame and roughly in a conical or dome shape as we are expecting occasional strong winds. This frame would be anchored into the ground in at least 15-30 places (internal steel posts), so I imagine the whole house will be somewhat similar to a faraday cage, and although lower than the tree tops, it will be a very low resistance target for lightening. Given that the decent sized trees will be relatively close to the home I would prefer not to encourage the lightning to hit any of them and explode the timber / send a big tree crashing down onto the house.
I don't mind how much work goes into setting this up properly but I only want to do this once, not fixing and maintaining the system every few years, digging up and replacing rusty metal in the ground etc...
I have come up with 2 ideas to address this situation, 1 simple, 1 more complex.
Idea 1 (Simple):
Attach a lightning rod to the very top of the house that will ensure that it casts a greater than 45 degree shadow over the entire home (and preferably further). The only restriction here is that there will be a height limit. If the tower was to poke up higher than the tree tops (or even above 10m from the ground), the council (local government) will definitely get grumpy and we'll probably have to get some difficult permission / have to attach a flashing beacon for planes etc...
So long as it was lower than the trees I think we will be ok, but then the trees will be the highest point all around not the tower so it should protect the house but may not encourage lightning away from the trees.
If we were to go this way I have 2 questions:
Q A1:
The steel frame house by it's nature will be very grounded. The Lightening tower/rod will also be very grounded. Should I electrically connect the 2 together or keep the rod/cable/ground rod insulated from the house frame?
My reasoning here is that if they were insulated from each other, although both grounded, the lightning will likely go for the much higher tower/rod, then releasing most of the power directly into the ground, maybe only some power will flow from the ground back up into the house frame? Alternatively, if they were both directly electrically connected, the power would run down the rod and into the frame as well before it goes to ground. Would this increase the chances that if someone was near or touching the house frame or anything connected to it, that they could get a boot?
If we do connect the rod electrically to the frame is there any point running a separate cable / ground rod when the power can flow through the entire very heavy steel frame into ground through the many posts?
Q A2:
Is there more we can do to increase the electrical conductivity of the soil/cement around the buried house frame posts / Earth rods given that the soil is likely to be fairly dry? (the moisture at the top tends to drain down into the mountain). I would prefer not to use salt or anything that would speed up corrosion, and I believe most additives need moisture to be effective anyway. The steel posts are thick 'C' section and galvanised, but I'm guessing concrete is not the best conductor? Should we make a mud/clay mix of our own? Perhaps we could add a heap of metal shavings / drill swarf into the mix (good until it all rusts)? Other suggestions?
Idea 2 (More complex):
Snag a heap of second hand 2" to 4" diameter aluminium irrigation pipe (like a flag pole). Weld sections together to form a long pole close to the same height as the trees. Attach each pole along each tree trunk but not buried in the ground (not supposed to bury aluminium for lightning ground rods?). This would provide around 10-15 poles in a circle around the mountain top and the poles could be hidden from view by placing them on the side of the tree trunk away from the house. A thick copper cable (insulation stripped off), or a decent sized copper tube (thick water pipe?) would then be buried in sections, each end connecting to the aluminium poles to form a closed ring connecting all the poles at the bottom in the circle around the plateau. Possibly even sink in a copper ground rod between each pole and attached to the copper cable/tube for more ground contact.
Ideally, having the poles rise well above the tree tops would help insure the poles get hit before the trees, but again we face the council / aeroplane warning lights / eyesaw issues so we need to keep the pole tops below the tree tops.
I also thought of having the poles between the trees instead of leaning right up against them, but then we would have no tree support to hold them up and have to firmly anchor each pole in the ground and possibly provide a cable support at the top.
We really want to get away from making this thing seem like we are living in a cage.
I imagine that having 10-15 aluminium poles about 10-15 meters long each, and all connected together by a copper loop that is buried in the ground will provide an excellent, low resistance and very attractive path for lightening, even without the additional copper ground rods inserted between each pole for extra ground earthing to be sure.
However I wonder wether it will be enough, as right next to each pole is a very large electrical collector network (tree branches), though it will then have to go through a much higher resistance cable (tree trunk), but again is able to distribute the power into the ground through a very large Earth rod network (tree roots).
If we could provide a way to electrically couple the tree to the pole, may they be able to help each other? This page seems to suggest that the lighting would probably hit the tree first, go down the branches then jump to the pole (possibly just exploding the top part of the tree?): http://cr4.globalspec.com/comment/71350
Also, I am aware that special connectors will be required to join copper to aluminium, and that copper should not be placed above aluminium due to incompatibility of the two metals leading to accelerated corrosion?
One extra benefit of this much higher cost and effort design is that instead of using cable buried for the in-ground loop, we could run buried pipes to connect all the vertical poles and put sprinklers on top of each pole effectively doubling the system's use as a bushfire sprinkler system that surrounds the house. With the pipes full of water they are only likely to decrease the electrical resistance and this fire protection would help justify the effort.
This idea presents several questions:
Q B1:
Would this approach do more to prevent lightning strikes as it might provide more ability for built up static to dissipate to ground before it reaches a critical mass (more metal exposed to air and spread around the site)?
Q B2:
Would the lightning more likely still go for the trees because they are still higher than the poles and have larger collectors, or would it more likely prefer the poles because they offer lower resistance to ground?
Q B3:
Should we electrically insulate the poles from the trees (tie the poles with rope?) to further discourage the trees from getting hit, or should we do our best to electrically connect the poles and trees (tie the poles with metal cable/strapping in several places?) so any power that does hit the tree tops will better flow into the pole offering an easier path to ground than just wood and hopefully reducing damage to the tree?
Q B4:
Should we add another cable loop (aluminium) connecting all the poles at their tops as well, to provide an in-air collector ring to further attract lightning rather than just 10-15 pole tops slightly below the tree tops? (Would prefer not to do this, would like to keep the whole system as hidden as possible).
Going further with this, we could even criss-cross a cable (or 2) from the top of one pole across to the top of a pole on the other side providing a hanging cable (simple net) well above the home but directly over it? (again, really would prefer not to have cables in view if possible).
Q B5:
I would like to weld a cover over the top of each pole so rain doesn't get in them. I have seen some lightning rods with a ball on top, I see other tops as just a single sharp pointy stick, and sometimes even a prickly porcupine of 5 or more sharp sticks pointing in various directions. Given that there is likely to be tree top branches hanging around near the top of the poles, would any of these pole tops make any difference?
Q B6:
Again both the house frame and this outer pole/cable loop shield will be connected to ground, but would there be any advantage to directly electrically connect them together with a metal conductor, or would it be better that they are only connected through the ground (provide some isolation for the people in the home)?
Q B7:
Is a round tube as good a conductor as a solid rod with the same cross-sectional area of metal?
(Do flag poles ever melt / get damaged from lightning strikes?)
Q B8:
One of the advantages of living high up is the reception (transmission and receiving of frequencies). At what point does this crude faraday cage begin to affect this? I assume this would be dependant upon the wavelength of the frequency and the size of the gaps between the poles and cables?
So many questions...
...answer as many or as few as you feel you can contribute to.
I hope this is an interesting challenge for you guys. My lady and I would appreciate any thoughts you have on these two approaches, or any other ideas to help us safely continue to enjoy the light show.
I am sorry this is so long, again I like to be thorough and hope this will provide some excellent advice/direction for others planning a similar build.
We have been looking around and feel this would be an appropriate forum full of good knowledgeable people to ask a few challenging questions.
The missus an I are about to build a house on a mountain top that is the highest peak for at least 1-2 km's (1 mile or more). Obviously because of the position we will need to take lightning protection very seriously and I feel we should probably get this done before we even start on the house. Also I tend to 5x over-engineer things just to be sure, and using second-hand industrial waste (cheap) wherever possible.
The mountain is covered in trees, dense in some places and spaced out in other parts. On the very top is a small, cleared, flat plateau of about 30-40 meters (32-43 yards) diameter. We will take down most of the small bushy trees near the top to open up the view, but we have decided to keep a circle of the biggest & tallest trees around the top edge to keep some shade and to help obscure the house into the skyline. Without the small trees, the occasional big trunks won't block our views too much. I believe that as long as these big trees all remain higher than the house (which will be roughly in the center of the flat plateau), they should help with some degree of lightning protection.
The house is likely to be constructed primarily of a heavy gauge steel frame and roughly in a conical or dome shape as we are expecting occasional strong winds. This frame would be anchored into the ground in at least 15-30 places (internal steel posts), so I imagine the whole house will be somewhat similar to a faraday cage, and although lower than the tree tops, it will be a very low resistance target for lightening. Given that the decent sized trees will be relatively close to the home I would prefer not to encourage the lightning to hit any of them and explode the timber / send a big tree crashing down onto the house.
I don't mind how much work goes into setting this up properly but I only want to do this once, not fixing and maintaining the system every few years, digging up and replacing rusty metal in the ground etc...
I have come up with 2 ideas to address this situation, 1 simple, 1 more complex.
Idea 1 (Simple):
Attach a lightning rod to the very top of the house that will ensure that it casts a greater than 45 degree shadow over the entire home (and preferably further). The only restriction here is that there will be a height limit. If the tower was to poke up higher than the tree tops (or even above 10m from the ground), the council (local government) will definitely get grumpy and we'll probably have to get some difficult permission / have to attach a flashing beacon for planes etc...
So long as it was lower than the trees I think we will be ok, but then the trees will be the highest point all around not the tower so it should protect the house but may not encourage lightning away from the trees.
If we were to go this way I have 2 questions:
Q A1:
The steel frame house by it's nature will be very grounded. The Lightening tower/rod will also be very grounded. Should I electrically connect the 2 together or keep the rod/cable/ground rod insulated from the house frame?
My reasoning here is that if they were insulated from each other, although both grounded, the lightning will likely go for the much higher tower/rod, then releasing most of the power directly into the ground, maybe only some power will flow from the ground back up into the house frame? Alternatively, if they were both directly electrically connected, the power would run down the rod and into the frame as well before it goes to ground. Would this increase the chances that if someone was near or touching the house frame or anything connected to it, that they could get a boot?
If we do connect the rod electrically to the frame is there any point running a separate cable / ground rod when the power can flow through the entire very heavy steel frame into ground through the many posts?
Q A2:
Is there more we can do to increase the electrical conductivity of the soil/cement around the buried house frame posts / Earth rods given that the soil is likely to be fairly dry? (the moisture at the top tends to drain down into the mountain). I would prefer not to use salt or anything that would speed up corrosion, and I believe most additives need moisture to be effective anyway. The steel posts are thick 'C' section and galvanised, but I'm guessing concrete is not the best conductor? Should we make a mud/clay mix of our own? Perhaps we could add a heap of metal shavings / drill swarf into the mix (good until it all rusts)? Other suggestions?
Idea 2 (More complex):
Snag a heap of second hand 2" to 4" diameter aluminium irrigation pipe (like a flag pole). Weld sections together to form a long pole close to the same height as the trees. Attach each pole along each tree trunk but not buried in the ground (not supposed to bury aluminium for lightning ground rods?). This would provide around 10-15 poles in a circle around the mountain top and the poles could be hidden from view by placing them on the side of the tree trunk away from the house. A thick copper cable (insulation stripped off), or a decent sized copper tube (thick water pipe?) would then be buried in sections, each end connecting to the aluminium poles to form a closed ring connecting all the poles at the bottom in the circle around the plateau. Possibly even sink in a copper ground rod between each pole and attached to the copper cable/tube for more ground contact.
Ideally, having the poles rise well above the tree tops would help insure the poles get hit before the trees, but again we face the council / aeroplane warning lights / eyesaw issues so we need to keep the pole tops below the tree tops.
I also thought of having the poles between the trees instead of leaning right up against them, but then we would have no tree support to hold them up and have to firmly anchor each pole in the ground and possibly provide a cable support at the top.
We really want to get away from making this thing seem like we are living in a cage.
I imagine that having 10-15 aluminium poles about 10-15 meters long each, and all connected together by a copper loop that is buried in the ground will provide an excellent, low resistance and very attractive path for lightening, even without the additional copper ground rods inserted between each pole for extra ground earthing to be sure.
However I wonder wether it will be enough, as right next to each pole is a very large electrical collector network (tree branches), though it will then have to go through a much higher resistance cable (tree trunk), but again is able to distribute the power into the ground through a very large Earth rod network (tree roots).
If we could provide a way to electrically couple the tree to the pole, may they be able to help each other? This page seems to suggest that the lighting would probably hit the tree first, go down the branches then jump to the pole (possibly just exploding the top part of the tree?): http://cr4.globalspec.com/comment/71350
Also, I am aware that special connectors will be required to join copper to aluminium, and that copper should not be placed above aluminium due to incompatibility of the two metals leading to accelerated corrosion?
One extra benefit of this much higher cost and effort design is that instead of using cable buried for the in-ground loop, we could run buried pipes to connect all the vertical poles and put sprinklers on top of each pole effectively doubling the system's use as a bushfire sprinkler system that surrounds the house. With the pipes full of water they are only likely to decrease the electrical resistance and this fire protection would help justify the effort.
This idea presents several questions:
Q B1:
Would this approach do more to prevent lightning strikes as it might provide more ability for built up static to dissipate to ground before it reaches a critical mass (more metal exposed to air and spread around the site)?
Q B2:
Would the lightning more likely still go for the trees because they are still higher than the poles and have larger collectors, or would it more likely prefer the poles because they offer lower resistance to ground?
Q B3:
Should we electrically insulate the poles from the trees (tie the poles with rope?) to further discourage the trees from getting hit, or should we do our best to electrically connect the poles and trees (tie the poles with metal cable/strapping in several places?) so any power that does hit the tree tops will better flow into the pole offering an easier path to ground than just wood and hopefully reducing damage to the tree?
Q B4:
Should we add another cable loop (aluminium) connecting all the poles at their tops as well, to provide an in-air collector ring to further attract lightning rather than just 10-15 pole tops slightly below the tree tops? (Would prefer not to do this, would like to keep the whole system as hidden as possible).
Going further with this, we could even criss-cross a cable (or 2) from the top of one pole across to the top of a pole on the other side providing a hanging cable (simple net) well above the home but directly over it? (again, really would prefer not to have cables in view if possible).
Q B5:
I would like to weld a cover over the top of each pole so rain doesn't get in them. I have seen some lightning rods with a ball on top, I see other tops as just a single sharp pointy stick, and sometimes even a prickly porcupine of 5 or more sharp sticks pointing in various directions. Given that there is likely to be tree top branches hanging around near the top of the poles, would any of these pole tops make any difference?
Q B6:
Again both the house frame and this outer pole/cable loop shield will be connected to ground, but would there be any advantage to directly electrically connect them together with a metal conductor, or would it be better that they are only connected through the ground (provide some isolation for the people in the home)?
Q B7:
Is a round tube as good a conductor as a solid rod with the same cross-sectional area of metal?
(Do flag poles ever melt / get damaged from lightning strikes?)
Q B8:
One of the advantages of living high up is the reception (transmission and receiving of frequencies). At what point does this crude faraday cage begin to affect this? I assume this would be dependant upon the wavelength of the frequency and the size of the gaps between the poles and cables?
So many questions...
...answer as many or as few as you feel you can contribute to.
I hope this is an interesting challenge for you guys. My lady and I would appreciate any thoughts you have on these two approaches, or any other ideas to help us safely continue to enjoy the light show.
I am sorry this is so long, again I like to be thorough and hope this will provide some excellent advice/direction for others planning a similar build.