I was told of an easy way to sink earth rods made from copper pipes long ago. I tried it several times and it always worked on the clay soil in these parts. Basically, flatten the end of the copper pipe - but not closing it right off. Put a garden hose pipe on the other end, secured with a jubilee clip or similar. Turn on the water supply and point the flattened end of the pipe at the ground. Rotate the pipe gently back and forth. Watch the pipe sink steadily into the ground! Remove the hose and solder another length of pipe on the end, reattach the hose and turn on the water. Repeat until you have sunk the pipe as low as it will go or as deep as you require. This wouldn't work on rocky ground, obviously, but on clay or sandy soil, it works really well. Hope this is of interest.
Another Pennsylvanian here, in aptly named Rockland Township. I was dreading putting my ground rod in. I used a hammer drill with a ground rod adapter bit. It went in a good 7 feet before it hit, leaving me a foot above ground for lightning suppression and other connections, so i called that close enough for amateur radio. = 73, AK2QJ
OG, You do a great job of illustrating how grounding works. However, in the situation of the of a shallow berried grounding electrode. You can run into the issue of loosing your ground when conditions are very dry. This is why the NEC requires this kind of ground to be at least 3 foot deep and 20' long... Even at 3 foot deep you can loose much of the grounding capacity when the soil dries out. Like my soil does during the summer on a mountain side in high dessert. It gets very dry down 6' to 10' feet or more depending on location. Also when installing this kind of ground. You don't need to use ground rods. A simple piece of #6 solid bare copper wire works best. My solution for this situation would be to install a ground ring all the way around the house. If possible. locate and bond it to the house grounding electrode system even if you have to go into the electrical panel to tie it in.
I have a 3', carbide drill bit with two 3' extensions. I'm an electrician and use them all the time when I hit rocks/obstacles. 5/8" carbide works great! Just sharing an idea that may help someone. 73
I only have a medium sized hammer-drill, but using carbide tipped HAMMER-DRILL RATED drill bits IT will go through damn near anything Iy you just take your time.. When I was younger I'd wished I'd bought a bigger drill, but now that I'm older (and not as strong), I'm glad I didn't get the heavier one. The bigger STS drill bits also have an attachment for actually driving the ground rods. (All your friends will love you too).
Nice video! I'm in Arizona. There are a couple of good options here: 1) Irrigated grounds, where your normal landscape watering system has outlets at the ground rods; and 2) Drive ground rods into septic drain field.
Whenever I need to put in a ground rod I go to home depot and buy 3/4 inch OD copper pipe. I then solder on this...( 3/4 in. Copper Pressure Cup x FIP Female Adapter Fitting) from HomeDepot. I then connect this (3/4 in. MIP Inlet x 3/4 in. MHT Outlet Brass Threaded Hose Bibb) I connect the hose... and at the other end, I slightly crimp the end of the copper tube, so it squirts a heavy stream of water. I stick that end in the dirt and the water pressure slowly digs a hole by displacing the soil enough so that the rod digs itself into the ground. This way, it's easier. Works in all kind of soil, even clay. Leave 6 inches above the ground and disconnect the threaded hose bibb. Now your done. Alot easier than banging a ground rod into the dirt.
My very rocky ground made me think it was impossible for me to install a ground on my own, but it turned out all I needed was a more powerful hammer-drill and a proper "ground rod adapter". The hammer-drill I rented from my local DIY center, the adapter I found online for $20. With them I was able to drive in two 5' rods and one 4' rod in a line six feet from each other, connect them together with #6 bare stranded copper wire and had enough wire left to attach the end of it to the base of my 2'x4' metal shed. Don't know if the shed will add much ground effect but I figured it couldn't hurt. It's not the star ground I wanted originally but the series ground should do nicely.
Living here in South Florida we don't have ground, we have limestone. So I like the idea of the trenching and I really didn't know anything about that ground material. So after 50 years you can teach a dog new tricks! Bill KG2CS
Hi Dave, Thanks for the video explanation. I did use water to eliminate the air spaces when I refilled the trench. There must have been a piece of ledge because I went 12 feet away and was able to get a ground rod in vertically. Never used Cadweld on any of the ground rods. They all protrude above ground about 4 inches. I might redo the grounds and use Cadweld when connecting them all together. Stay safe. 73 WJ3U
Hello dave I read somewhere (cannot recall where) about alternative means of grounding. It involved wirevmesh, a ground rod and coarse salt. The process involved shallow excavation of an area large enough to accommodate the mesh which I believe was 6' square. Next, lay the ground rod on the mesh and wire tie it to the mesh. The end of the ground rod can be bent 90 degrees so that it will protrude above the surface when the whole thing is covered with excavated earth. When backfilling, mix the material with coarse salt which I suppose increases the conductivity of the earth. I can foresee a problem with this method - namely the corrosive nature of salt. I would suspect that after a few years there may be little - if anything left of your ground system. What's your opinion on this?
Ufer grounds have a significant risk. “A disadvantage of Ufer grounds is that the moisture in the concrete can flash into steam during a lightning strike or similar high energy fault condition. This can crack the surrounding concrete and damage the building foundation.” (From Ufer Wiki). For the amateur, this form of ground for antennas (aka, “aerial lightning electrodes”) is likely undesirable. I should also note that the numerous Ufer grounds I have installed all required the rebar to be electrically connected via CadWeld by a large (#2) bare copper conductor. Finally, per the NEC, ground must have a maximum resistance of 25-ohms utilizing accepted measurement techniques.
As a fellow Pennsylvanian, I can completely relate to Don's problem. With all the rocks in PA soil, it was a total nightmare installing my shacks and antennas ground rods and especially when I dug a hole to cement in the base for my 6BTV antenna.
I have always planted earth rod at a distance of 8-10 times the length of the rod itself, closing everything in a ring, this is the rule that an engineer taught me, obviously there are the variables on the type of soil etc., I simply lay the rod or earth horizontally in the excavation, and I do 8 / max 10 times its length to mark where to plant the next one.
For bonding between ground rods, use bare stranded wire and bury it. It adds a bit to the grounding effectiveness at the same time it's bonding the ground rods.
@@davecasler Thank you David. I will have to find some that does not cost much, ha ha. I do have single wire for support of the antenna pole going to ground, and same wire running back to the house grounded directly to the house grounding pole. I also ran my coax along the wire line going to the house as well but I will look for stranded wire to run from antenna supporting pole to ground rod. Thanks again for your time and explanation. George, Alberta Canada
The certain way to know if a ground is effective enough is to use a clamp-on ground resistance earth tester. You put it around a ground rod or anything metallic attached to the Earth. If your reading is 0 ohms, then your ground is as good as it is going to get. If you get infinite resistance, then your ground rod is completely ineffective. The NFPA and IEEE require a resistance of less than 5 ohms.
I'm in a super rocky area but have some moisture, I ended up putting 2' ground rods every 4 feet in a 20x20 square and bonding them all together. Ground moisture is high but there is a lot of granite all over.
Hmm, by my measurement, using the shortest path, I would need to do a whole lot of digging and about 225 ft of copper #6 wire to bond to my home's grounding rod. This is based on where my radio is, the location of the rod and existing patios that are in the way.
Just a warning that the domestic earthing system in the UK is different to the US and there are implications for the radio amateur. It can be dangerous to stick a rod in the ground without having it checked by a qualified electrician, because it needs to be bonded to the MET, even if it's an RF Earth. See RSGB for info.
Thanks Dave, there's something you didn't cover and was wondering if it works at all,, What if your house is on a slab and you drill into it using a long studded bolt,,, Would that work ? Thanks Ron AC7RH
I've read that there should only be one ground junction IN the house, and that should be the star ground all your equipment is attatched to. All external grounds should be just that, EXTERNAL to your house or shack - not internal or through it..
the heck with buying ground rod enhancement crap, you can to the same thing free when you have to pee go pee on the ground rod! ive done it for years and works very well and also you can put rock salt down around it.
Your comment would not pass any attempt at fact-checking. Please see at my reply to another comment on this thread for more details. Sharing misinformation with respect to electrical safety can have lethal consequences. Per NEC Article 250: Grounding electrode: A conducting object through which a direct connection to earth is established. Common grounding electrodes include rods, plates, pipes, ground rings, metal in-ground support structures and concrete-encased electrodes. All grounding electrodes at each building or structure shall be bonded together to form the grounding electrode system.
I thought multiple grounds were what’s needed but I’m not even the thinking about house tie in just antennas and towers or poles . We do that and cad weld when possible but at my home there not welded so have to check connections several times a year and they do get loose .
Before you install a bunch of ground rods consider this electrons follow the path of least resistance its a fact. If you have what I call a super ground 10, 20 or even 100 times better then the houses around you guess where the power surge is going. Its also against national code to have more then one ground rod connected to your house electrical system. Im very happy with my average ground. Ham from 1991 and never lost any electronic equipment from lightning or power surge knock on wood
I don't know where you live but I thought the code in the US dictated to use at least a second rod if the first one failed to be low enough resistance.
No! I don't think you understand the basic concepts of grounding! I've been an electrician for 35 years and NEC REQUIRES: "a ground system shall have a grounding resistance of 25 ohms or less. Achieving this may require more than one ground rod, or multiple ground rods. The rods must be at least six feet apart." While it is true that electrons usually follow the path of least resistance (but not always), this is why you should have a good ground SYSTEM. A typical lightning flash is about 300 million Volts at about 30,000 Amps!!! Even a lightning strike in a neighbor's yard can easily be in the millions of volts when it arrives at your house. Yes, it will flow to the path with the least resistance (your ground system) and that's exactly what you want!!! A good ground SYSTEM will keep everything in your house at the same potential! It doesn't matter if it's a few million Volts, if it's all at the same potential, there is no difference in potential! Using basic ohm's law, if your single ground rod has 100 ohm's (very typical for a single ground rod in a typical area of the country) you have a MAJOR difference in potential. Let's assume your only at 1/10th the power of a lightning strike, E=I x R or 3,000 amps times 100 ohms (in the ground rod), you have 300,000 Volts!! A good ground SYSTEM will keep the difference near zero. The issue is NOT attracting lightning, it's keeping everything at the same, or at nearly the same, potential.
My electric co has a grounding copper pan on the bottom of my electric pole with a #6 copper wire up the side of the pole. (Pole is dedicated to my QTH), then they have a regular 8' copper ground rod suknen right next to the pole itself, then they make a 30'-40' run underground to the breaker panel on the side of the house with it's own 8' sunken ground rod. I've not had any issues in 20 years with lightening in the south central Texas weather. Knock on wood! KI5IQE
You can have more than one ground rod, but all must be bonded together and bonded to the one at the service entrance with minimum #6 AWG copper or equivalent. NEC 250.53 Grounding Electrode System Installation. (B) Electrode Spacing. Where more than one of the electrodes of the type specified in 250.52(A)(5) or (A)(7) are used, each electrode of one grounding system (including that used for air terminals) shall not be less than 1.83 m (6 ft) from any other electrode of another grounding system. Two or more grounding electrodes that are bonded together shall be considered a single grounding electrode system. NEC Article 810 covers antenna systems (including satellite dishes) for radio and television receiving equipment, and amateur and citizen band radio transmitting and receiving equipment. The grounding requirements for antenna cables are contained in 810.20(C) and 810.21 Mike Holt has a PDF online that covers NEC 810 with lots of illustrations: Search for and download: Radio_and_Television_2014NEC.pdf Also search for and download: Motorola R56_2005.PDF “Standards and Guidelines for Communication Sites The NEC requires a minimum spacing of 6 feet, and Motorola says the optimal spacing is 2 times the rod length, so, for 8 foot rods, space them approximately every 16 ft.
I was told of an easy way to sink earth rods made from copper pipes long ago.
I tried it several times and it always worked on the clay soil in these parts.
Basically, flatten the end of the copper pipe - but not closing it right off.
Put a garden hose pipe on the other end, secured with a jubilee clip or similar.
Turn on the water supply and point the flattened end of the pipe at the ground.
Rotate the pipe gently back and forth.
Watch the pipe sink steadily into the ground!
Remove the hose and solder another length of pipe on the end, reattach the hose and turn on the water.
Repeat until you have sunk the pipe as low as it will go or as deep as you require.
This wouldn't work on rocky ground, obviously, but on clay or sandy soil, it works really well.
Hope this is of interest.
Another Pennsylvanian here, in aptly named Rockland Township. I was dreading putting my ground rod in. I used a hammer drill with a ground rod adapter bit. It went in a good 7 feet before it hit, leaving me a foot above ground for lightning suppression and other connections, so i called that close enough for amateur radio. = 73, AK2QJ
OG, You do a great job of illustrating how grounding works.
However, in the situation of the of a shallow berried grounding electrode. You can run into the issue of loosing your ground when conditions are very dry. This is why the NEC requires this kind of ground to be at least 3 foot deep and 20' long... Even at 3 foot deep you can loose much of the grounding capacity when the soil dries out.
Like my soil does during the summer on a mountain side in high dessert. It gets very dry down 6' to 10' feet or more depending on location.
Also when installing this kind of ground. You don't need to use ground rods. A simple piece of #6 solid bare copper wire works best.
My solution for this situation would be to install a ground ring all the way around the house. If possible. locate and bond it to the house grounding electrode system even if you have to go into the electrical panel to tie it in.
I have a 3', carbide drill bit with two 3' extensions. I'm an electrician and use them all the time when I hit rocks/obstacles.
5/8" carbide works great!
Just sharing an idea that may help someone. 73
I only have a medium sized hammer-drill, but using carbide tipped HAMMER-DRILL RATED drill bits IT will go through damn near anything Iy you just take your time..
When I was younger I'd wished I'd bought a bigger drill, but now that I'm older (and not as strong), I'm glad I didn't get the heavier one.
The bigger STS drill bits also have an attachment for actually driving the ground rods. (All your friends will love you too).
Nice video! I'm in Arizona. There are a couple of good options here: 1) Irrigated grounds, where your normal landscape watering system has outlets at the ground rods; and 2) Drive ground rods into septic drain field.
Whenever I need to put in a ground rod I go to home depot and buy 3/4 inch OD copper pipe. I then solder on this...( 3/4 in. Copper Pressure Cup x FIP Female Adapter Fitting) from HomeDepot.
I then connect this (3/4 in. MIP Inlet x 3/4 in. MHT Outlet Brass Threaded Hose Bibb) I connect the hose... and at the other end, I slightly crimp the end of the copper tube, so it squirts a heavy stream of water. I stick that end in the dirt and the water pressure slowly digs a hole by displacing the soil enough so that the rod digs itself into the ground. This way, it's easier. Works in all kind of soil, even clay. Leave 6 inches above the ground and disconnect the threaded hose bibb. Now your done. Alot easier than banging a ground rod into the dirt.
Thanks for the next dose of necessary and valuable knowledge. Greetings from distant Poland - 73.
Good info on the Ground Enhancement Material. Thanks. As always, your videos are concise and very informative.
My very rocky ground made me think it was impossible for me to install a ground on my own, but it turned out all I needed was a more powerful hammer-drill and a proper "ground rod adapter". The hammer-drill I rented from my local DIY center, the adapter I found online for $20. With them I was able to drive in two 5' rods and one 4' rod in a line six feet from each other, connect them together with #6 bare stranded copper wire and had enough wire left to attach the end of it to the base of my 2'x4' metal shed. Don't know if the shed will add much ground effect but I figured it couldn't hurt. It's not the star ground I wanted originally but the series ground should do nicely.
Living here in South Florida we don't have ground, we have limestone. So I like the idea of the trenching and I really didn't know anything about that ground material. So after 50 years you can teach a dog new tricks! Bill KG2CS
Hi Dave,
Thanks for the video explanation. I did use water to eliminate the air spaces when I refilled the trench. There must have been a piece of ledge because I went 12 feet away and was able to get a ground rod in vertically. Never used Cadweld on any of the ground rods. They all protrude above ground about 4 inches. I might redo the grounds and use Cadweld when connecting them all together. Stay safe. 73 WJ3U
Lots of great info in this one Dave. Thanks!
We have used pure copper pipe layed out horizontal with engagement powder. Works for heave rock ground.
Hello dave
I read somewhere (cannot recall where) about alternative means of grounding. It involved wirevmesh, a ground rod and coarse salt. The process involved shallow excavation of an area large enough to accommodate the mesh which I believe was 6' square. Next, lay the ground rod on the mesh and wire tie it to the mesh. The end of the ground rod can be bent 90 degrees so that it will protrude above the surface when the whole thing is covered with excavated earth. When backfilling, mix the material with coarse salt which I suppose increases the conductivity of the earth.
I can foresee a problem with this method - namely the corrosive nature of salt. I would suspect that after a few years there may be little - if anything left of your ground system. What's your opinion on this?
Should also consider "ground plates". 2 sq feet of 1/4 inch steel is considered grounding. NEC states 30" below ground.
Ufer grounds have a significant risk. “A disadvantage of Ufer grounds is that the moisture in the concrete can flash into steam during a lightning strike or similar high energy fault condition. This can crack the surrounding concrete and damage the building foundation.” (From Ufer Wiki).
For the amateur, this form of ground for antennas (aka, “aerial lightning electrodes”) is likely undesirable.
I should also note that the numerous Ufer grounds I have installed all required the rebar to be electrically connected via CadWeld by a large (#2) bare copper conductor. Finally, per the NEC, ground must have a maximum resistance of 25-ohms utilizing accepted measurement techniques.
As a fellow Pennsylvanian, I can completely relate to Don's problem. With all the rocks in PA soil, it was a total nightmare installing my shacks and antennas ground rods and especially when I dug a hole to cement in the base for my 6BTV antenna.
I have always planted earth rod at a distance of 8-10 times the length of the rod itself, closing everything in a ring, this is the rule that an engineer taught me, obviously there are the variables on the type of soil etc., I simply lay the rod or earth horizontally in the excavation, and I do 8 / max 10 times its length to mark where to plant the next one.
Dave, I guess you know your next Ask Dave video will be number 500! Are you planning something special?
I was going to asked you that same question next week. Thanks
Good video as always. My ic705 mobile has a ground, best way to ground and stay mobile?
TeamReplay for the win!
hello, what did you mean by using No.6 "unshielded" stranded wire? The wire should not have any plastic coat / jacket? Just bare wire?
For bonding between ground rods, use bare stranded wire and bury it. It adds a bit to the grounding effectiveness at the same time it's bonding the ground rods.
@@davecasler Thank you David. I will have to find some that does not cost much, ha ha. I do have single wire for support of the antenna pole going to ground, and same wire running back to the house grounded directly to the house grounding pole. I also ran my coax along the wire line going to the house as well but I will look for stranded wire to run from antenna supporting pole to ground rod. Thanks again for your time and explanation.
George, Alberta Canada
The certain way to know if a ground is effective enough is to use a clamp-on ground resistance earth tester. You put it around a ground rod or anything metallic attached to the Earth. If your reading is 0 ohms, then your ground is as good as it is going to get. If you get infinite resistance, then your ground rod is completely ineffective. The NFPA and IEEE require a resistance of less than 5 ohms.
I'm in a super rocky area but have some moisture, I ended up putting 2' ground rods every 4 feet in a 20x20 square and bonding them all together. Ground moisture is high but there is a lot of granite all over.
How in the world do you find the LIVE "Ask Dave" UA-cam streams? I'm going nuts trying to find out and listen to his broadcasts.
Hmm, by my measurement, using the shortest path, I would need to do a whole lot of digging and about 225 ft of copper #6 wire to bond to my home's grounding rod. This is based on where my radio is, the location of the rod and existing patios that are in the way.
I have 2 each 8' copper on the horizontally about 4 feet deep. Thank you.
Just a warning that the domestic earthing system in the UK is different to the US and there are implications for the radio amateur. It can be dangerous to stick a rod in the ground without having it checked by a qualified electrician, because it needs to be bonded to the MET, even if it's an RF Earth. See RSGB for info.
Ground enhancement material.................we called that rock salt, just mix a bit with the soil around the ground rod.
Thanks Dave, there's something you didn't cover and was wondering if it works at all,,
What if your house is on a slab and you drill into it using a long studded bolt,,, Would that work ?
Thanks
Ron AC7RH
Can one bond from one side of the house to the other through the basement?
I've read that there should only be one ground junction IN the house, and that should be the star ground all your equipment is attatched to.
All external grounds should be just that, EXTERNAL to your house or shack - not internal or through it..
the heck with buying ground rod enhancement crap, you can to the same thing free when you have to pee go pee on the ground rod! ive done it for years and works very well and also you can put rock salt down around it.
Great info Dave. From Crossville TN where bedrock runs from 18 to 36 inches everywhere. Will you be giving away that Icom 7300? LOL. 73s, Tom KC9MDN
I drove to Crossville in 2017 to watch the total solar eclipse. Did you watch it, Tom?
@@ricke.2205 No, just moved here in 2019.
Another explosive knowledge bomb from the King of all Elmers. :)
you want 10 oams or less for grounding
I knew a guy who would poor salt water over his ground rod
I like to use copper sulfate - also sold in plumbing depts.
Great information...thank you Dave! Frank KJ7LAN
multiple ground rods are a No no with the National electrical code. for VERY good reasons!!
Your comment would not pass any attempt at fact-checking. Please see at my reply to another comment on this thread for more details. Sharing misinformation with respect to electrical safety can have lethal consequences.
Per NEC Article 250:
Grounding electrode: A conducting object through which a direct connection to earth is established. Common grounding electrodes include rods, plates, pipes, ground rings, metal in-ground support structures and concrete-encased electrodes. All grounding electrodes at each building or structure shall be bonded together to form the grounding electrode system.
I thought multiple grounds were what’s needed but I’m not even the thinking about house tie in just antennas and towers or poles . We do that and cad weld when possible but at my home there not welded so have to check connections several times a year and they do get loose .
This information seems a bit suss.
Before you install a bunch of ground rods consider this electrons follow the path of least resistance its a fact. If you have what I call a super ground 10, 20 or even 100 times better then the houses around you guess where the power surge is going. Its also against national code to have more then one ground rod connected to your house electrical system. Im very happy with my average ground. Ham from 1991 and never lost any electronic equipment from lightning or power surge knock on wood
I don't know where you live but I thought the code in the US dictated to use at least a second rod if the first one failed to be low enough resistance.
@@g0fvt sorry one good ground rod.
No! I don't think you understand the basic concepts of grounding!
I've been an electrician for 35 years and NEC REQUIRES: "a ground system shall have a grounding resistance of 25 ohms or less. Achieving this may require more than one ground rod, or multiple ground rods. The rods must be at least six feet apart."
While it is true that electrons usually follow the path of least resistance (but not always), this is why you should have a good ground SYSTEM. A typical lightning flash is about 300 million Volts at about 30,000 Amps!!! Even a lightning strike in a neighbor's yard can easily be in the millions of volts when it arrives at your house. Yes, it will flow to the path with the least resistance (your ground system) and that's exactly what you want!!! A good ground SYSTEM will keep everything in your house at the same potential! It doesn't matter if it's a few million Volts, if it's all at the same potential, there is no difference in potential!
Using basic ohm's law, if your single ground rod has 100 ohm's (very typical for a single ground rod in a typical area of the country) you have a MAJOR difference in potential.
Let's assume your only at 1/10th the power of a lightning strike, E=I x R or 3,000 amps times 100 ohms (in the ground rod), you have 300,000 Volts!! A good ground SYSTEM will keep the difference near zero. The issue is NOT attracting lightning, it's keeping everything at the same, or at nearly the same, potential.
My electric co has a grounding copper pan on the bottom of my electric pole with a #6 copper wire up the side of the pole. (Pole is dedicated to my QTH), then they have a regular 8' copper ground rod suknen right next to the pole itself, then they make a 30'-40' run underground to the breaker panel on the side of the house with it's own 8' sunken ground rod. I've not had any issues in 20 years with lightening in the south central Texas weather. Knock on wood! KI5IQE
You can have more than one ground rod, but all must be bonded together and bonded to the one at the service entrance with minimum #6 AWG copper or equivalent.
NEC 250.53 Grounding Electrode System Installation. (B) Electrode Spacing. Where more than one of the electrodes of the type specified in 250.52(A)(5) or (A)(7) are used, each electrode of one grounding system (including that used for air terminals) shall not be less than 1.83 m (6 ft) from any other electrode of another grounding system. Two or more grounding electrodes that are bonded together shall be considered a single grounding electrode system.
NEC Article 810 covers antenna systems (including satellite dishes) for radio and television receiving equipment, and amateur and citizen band radio transmitting and receiving equipment. The grounding requirements for antenna cables are contained in 810.20(C) and 810.21
Mike Holt has a PDF online that covers NEC 810 with lots of illustrations: Search for and download: Radio_and_Television_2014NEC.pdf
Also search for and download: Motorola R56_2005.PDF “Standards and Guidelines for Communication Sites
The NEC requires a minimum spacing of 6 feet, and Motorola says the optimal spacing is 2 times the rod length, so, for 8 foot rods, space them approximately every 16 ft.