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A grounding question please
- Thread starter MedMan4040
- Start date
If you had inverters that fed AC power into your house there would be a ground line from that equipment to your house AC panel that would have been inspected. If the power from the batteries and inverters never fed the house then maybe they consider it an island. I suspect when you repurposed it for radio use it was not inspected again and that does require bonding all the ground rods at the tower to your main AC panel ground, NEC is very specific about that.
And as I mentioned before if your tower gets hit by lightning and radios in your house connect to it you will have much more damage loosing TVs, radios, clocks, whatever is plugged into AC power in the house is at greater risk of damage when your house ground is at a different potential from the antenna and tower.
AC9KH
Member
It's a whole-house off-grid power system. The utility power can go out and we don't even know it because the house runs on inverter power all the time. If the utility goes out it just can't sell power back to the grid is all. At night it uses power back from the grid. If the utility goes out and never comes back on, and there's not enough solar to maintain the system, it will automatically start the generator and charge the battery up with that.
I don't care what NEC says, and I'll argue with any inspector that claims that tower has to be bonded to utility mains, and I'll win. It's been hit by lightning twice in the last 20 years and the only thing that saved our electrical equipment in the house was the fact that that tower is standalone. Both times, all it did was blow the bridge rectifier for the turbine, which is in a separate box outside the utility room mounted on 4x4 treated wood posts. The lightning damage traveled that far on wiring before it was stopped and never made it to the utility room. Put several thousand volts on your grounds in your house you'll blow everything in the house. The grounding system on that tower was designed to distribute a direct lightning hit over a large area because it is a huge lightning rod sticking up in the sky.
There is a setback exclusion in NEC just for this. Any inspector that shows up and tries to tell me otherwise will get the exclusion due to setback read to him and he can go pound sand.
Sounds like you make your own rules with lightning. Good luck with that.
AC9KH
Member
I didn't design it. A licensed engineer did. It was designed with a setback and grounding system to keep lightning damage out of the house. And it works. Although the second time in 2015 the EMF blew one of my ICOM 7200's, which had to be sent to Michigan for repairs. Both radios were off and the feedlines were disconnected outside the shack at the knife switches. But the voltage jumped the air gap on the knife switches.
AC9KH
Member
I had to drag out the engineering drawings and permits from our tower installation 24 years ago this summer. It was TEP that designed it. They got drawings of the "rolling sphere" protection zone around the tower, with all the equations, on the engineering site plan, which applies to not only towers, but also buildings and other tall structures.. I think H.I.G. has since acquired Tower Engineering Professionals. What I would suggest is maybe call them up and tell them they don't know what they're doing, see how that goes.
Or you could just check NEC and find that exclusion for this "rolling sphere" protection zone around a tower.
I had considered, when I get a crane in here to remove the dead wind turbine from it, picking up the tower with the crane and put base insulators on it, re-purpose the grounding system as the ground plane. Then I think it would be more successful as a 160m antenna vs being shunt-fed. But that introduces new problems like a spark-gap lightning arrestor and the fencing that would be required around the base of it. Right now it works good for supporting wire antennas so I don't know what I'm going to do with it yet.
Wow, a great discussion deteriorating fast...
In any case.... with the lightning and grounding protection being talked about, I think we're talking about the earth electrode part and what needs to be connected to it, and with what (at least based on the OP), and where.
I don't see how the rolling sphere thing gets involved at all.
I thought we were all talking about grounding, the avoidence of ground loops, and interconnections....
For the record... (pet peeve) The empire state building has survived multiple lightning strikes, so there are things that survive lightning strikes and continue to operate.
Thanks
Joel
In any case.... with the lightning and grounding protection being talked about, I think we're talking about the earth electrode part and what needs to be connected to it, and with what (at least based on the OP), and where.
I don't see how the rolling sphere thing gets involved at all.
I thought we were all talking about grounding, the avoidence of ground loops, and interconnections....
For the record... (pet peeve) The empire state building has survived multiple lightning strikes, so there are things that survive lightning strikes and continue to operate.
Thanks
Joel
- Joined
- Dec 19, 2002
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- 2,502
...and they are available in different sizes at Lowe's and other stores.
AC9KH
Member
And they come in aluminum, bare copper and clad copper.
AC9KH
Member
That came about due to an insistence that my tower has to be bonded to mains ground, which is not the case. And any wire antenna supported by it, not electrically connected to the tower and fed with coaxial cable, is already bonded to mains ground thru the coax shield and my shack bonding system.
Hams seem to have this idea that you need to run elaborate networks of ground rods, bonding wires etc because they seen it on the internet. But the hams that come up with this stuff are not using their ohmmeter or common sense.
I am a ham and I do watch YouTube videos on grounding. But mostly for amusement.
I was also a Principal Engineer and site RF Engineer in the satellite broadcast industry responsible for most big antenna installation projects (some upwards of $5mil). And I had to deal with outside engineers designing our grounding systems or I designed the grounding systems myself per NEC and R-56 and had to interface with our city inspectors for electrical and grounding. If I didn't design in or make sure the ground ring around a new antenna wasn't bonded back to the building main AC ground I would have been out of a job and I did this for 18yrs.
The antenna below is similar to what I'm talking about although its small, and it would have very similar grounding needs to the 120ft tower in question. This would include 8-12 10ft ground rods in a ring around the foundation and usually including UFER ground practices to the rebar in the foundation, bonded together with 500mcm cable then bonded to the AC panel main ground in the building housing all the electronics. All antennas like this on the property, and there were a lot of them are grounded back to a central point at the building AC mains.
The antenna below happens to be in Hawaii and built after my retirement. That's me working in the hub performing final acceptance testing on behalf of the mfr, installation vendor and the customer as I'm entrusted by all three to perform the measurements and produce a final report. I got tired of flying to Hawaii and all over the globe doing this in retirement so now my job is reading through RR and commenting on all your stuff.
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AC9KH
Member
Of course, but this is for ham radio antennas and stations. As per the OP's grounding system, is there really a need for it? I think he's doing this because he seen it on the internet. This is for safety grounds to eliminate potential between various pieces of equipment in the shack. In most cases, a shack RF ground is not even required for the antennas that most hams use unless it's an end-fed that uses earth ground to complete the RF circuit. So we're not considering that here.
So when it comes to safety grounds, let's not confuse lightning protection with the basic requirement that equipment be bonded to a common grounding point to eliminate potential. That common grounding point ain't gonna do nothing for lightning - its purpose is to prevent you from getting a lethal shock if there is a fault in equipment.
This is where hams need to get out their ohmmeter and start checking DC resistance before building an elaborate grounding bar with braid straps etc just because they seen it on the internet.
Take a basic ham radio shack powered from AC mains; you have a power supply. Ohm out the DC resistance between the chassis of that to the third grounding pin in the power plug. If it's a decent quality power supply you will find zero ohms. Plug that into the wall socket. Assuming the wiring in your facility (house or shack) is up to code, you can now check the DC resistance between the chassis of your power supply and your service entrance ground. You will find it is connected. Voila! The chassis of that power supply is your common grounding point in the shack, same as any electrical sub-panel in one of your outbuildings. You don't need no copper bar with a ground rod. Run a bonding wire from your radios or tuners to your power supply chassis ground point and you meet all requirements of NEC for safety ground.
And the above also includes your antenna(s). Put up a dipole with a balun on it, fed with coaxial feeder. Go to the feedpoint of that antenna, again use your ohmmeter and check DC resistance from the coax shield to your mains ground. You will find it is connected. Why? Because the coax shield is connected to the chassis of your radio or tuner, which is bonded to the power supply, which is bonded to the mains ground. No further action needed. You are in compliance.
Now, put in this copper grounding bar outside the shack with a ground rod, or connect it to your mains ground with a wire. This is where you run into potential violations of NEC on grounding due to a thing called the "sphere of influence" for ground rods. You just created another circuit, creating a ground loop. Most any inspector is going to require that the distance between ground rods connected to your mains is no more than 2x the length of the rod. Minimum distance is 6ft apart, but if that inspector finds another grounding point that's further apart than that, connected in a loop, he or she is going to teach you (the ham) what an ohmmeter is used for. You just opened a can of worms that you didn't have open.
So that's my point here; has the OP actually gotten his ohmmeter out and checked this? Or he just doing something because he seen it on the internet?
So when it comes to safety grounds, let's not confuse lightning protection with the basic requirement that equipment be bonded to a common grounding point to eliminate potential. That common grounding point ain't gonna do nothing for lightning - its purpose is to prevent you from getting a lethal shock if there is a fault in equipment.
This is where hams need to get out their ohmmeter and start checking DC resistance before building an elaborate grounding bar with braid straps etc just because they seen it on the internet.
Take a basic ham radio shack powered from AC mains; you have a power supply. Ohm out the DC resistance between the chassis of that to the third grounding pin in the power plug. If it's a decent quality power supply you will find zero ohms. Plug that into the wall socket. Assuming the wiring in your facility (house or shack) is up to code, you can now check the DC resistance between the chassis of your power supply and your service entrance ground. You will find it is connected. Voila! The chassis of that power supply is your common grounding point in the shack, same as any electrical sub-panel in one of your outbuildings. You don't need no copper bar with a ground rod. Run a bonding wire from your radios or tuners to your power supply chassis ground point and you meet all requirements of NEC for safety ground.
And the above also includes your antenna(s). Put up a dipole with a balun on it, fed with coaxial feeder. Go to the feedpoint of that antenna, again use your ohmmeter and check DC resistance from the coax shield to your mains ground. You will find it is connected. Why? Because the coax shield is connected to the chassis of your radio or tuner, which is bonded to the power supply, which is bonded to the mains ground. No further action needed. You are in compliance.
Now, put in this copper grounding bar outside the shack with a ground rod, or connect it to your mains ground with a wire. This is where you run into potential violations of NEC on grounding due to a thing called the "sphere of influence" for ground rods. You just created another circuit, creating a ground loop. Most any inspector is going to require that the distance between ground rods connected to your mains is no more than 2x the length of the rod. Minimum distance is 6ft apart, but if that inspector finds another grounding point that's further apart than that, connected in a loop, he or she is going to teach you (the ham) what an ohmmeter is used for. You just opened a can of worms that you didn't have open.
So that's my point here; has the OP actually gotten his ohmmeter out and checked this? Or he just doing something because he seen it on the internet?
The grounding I described is good for both NEC human safety and protection of equipment in a lightning strike. More equipment is damaged from huge differences in potential on the ground system than across the AC mains from phase to phase or from line to neutral, its been proven over and over.
If you have antenna mast or tower out in the yard grounded properly with ground rods but not bonded to the house main AC ground and lightning hits the antenna/mast there will be many thousands of volts difference on the coax shield compared to the grounded AC sockets in the house and lots of stuff blows up. Bonding the ground rods at the tower to the house main AC panel reduces resistance between grounds and keeps the tower ground and equipment ground in the house at a closer potential with less voltage difference in a strike. When things are adequately bonded the tower and house ground both take a huge jump in voltage together during a strike rather than the tower side taking a huge jump and discharging through equipment on the house side that stays closer to normal potential.
NEC requires a minimum of 6ga copper wire to bond any new ground rods to the house AC panel but if designing for lightning you would up that and 500mcm bare stranded copper with cad welded connections several feet below grade is very common in commercial installations.
If you have antenna mast or tower out in the yard grounded properly with ground rods but not bonded to the house main AC ground and lightning hits the antenna/mast there will be many thousands of volts difference on the coax shield compared to the grounded AC sockets in the house and lots of stuff blows up. Bonding the ground rods at the tower to the house main AC panel reduces resistance between grounds and keeps the tower ground and equipment ground in the house at a closer potential with less voltage difference in a strike. When things are adequately bonded the tower and house ground both take a huge jump in voltage together during a strike rather than the tower side taking a huge jump and discharging through equipment on the house side that stays closer to normal potential.
NEC requires a minimum of 6ga copper wire to bond any new ground rods to the house AC panel but if designing for lightning you would up that and 500mcm bare stranded copper with cad welded connections several feet below grade is very common in commercial installations.
AC9KH
Member
Adding to my above post, let's say you have a station that's not powered from your service entrance. You wanted a station that can operate in the event of a utility power outage. So this is an off-grid station that will be powered from either battery or generator, or maybe solar with batteries. Now you need what the OP is doing because you don't have that power supply that's bonded to your service entrance ground.
In this case, even it's possible, I would not connect your station safety ground to your service entrance ground. Make it standalone - it's not required to be connected to the service entrance ground because the station is off-grid. In theory, you can connect your station ground to the utility ground without creating a ground loop. But this can run into other problems with NEC and inspectors, especially if you are using a generator or inverter to power it. Some generators have bonded neutral, some don't. Most portable generators have a floating neutral. Same with inverters unless it's a very expensive one designed for whole-house power. In that case you're going to need to make the neutral-ground bond at the power panel (the service entrance) that powers your station and you do NOT want to electrically connect that to any point in your utility service entrance, including the grounds. Any inspector will fail such a thing.
If you are using solar panels to power an off-grid station be aware they also have a chassis ground that must be connected to your station ground and the code requirement for grounding solar panels is 6 AWG bare copper.
In this case, even it's possible, I would not connect your station safety ground to your service entrance ground. Make it standalone - it's not required to be connected to the service entrance ground because the station is off-grid. In theory, you can connect your station ground to the utility ground without creating a ground loop. But this can run into other problems with NEC and inspectors, especially if you are using a generator or inverter to power it. Some generators have bonded neutral, some don't. Most portable generators have a floating neutral. Same with inverters unless it's a very expensive one designed for whole-house power. In that case you're going to need to make the neutral-ground bond at the power panel (the service entrance) that powers your station and you do NOT want to electrically connect that to any point in your utility service entrance, including the grounds. Any inspector will fail such a thing.
If you are using solar panels to power an off-grid station be aware they also have a chassis ground that must be connected to your station ground and the code requirement for grounding solar panels is 6 AWG bare copper.
AC9KH
Member
This is true in most cases. However, with a tower such as mine that is a long distance from the service entrance, the inspector won't pass a long wire run to bond it due to impedance in the run. This is noted in the engineering drawings of my tower that I dug out yesterday.
When it comes to lightning, I think W.C. Alexander, Director of Engineering at Crawford summed it up quite well:
Despite the elaborate lightning protection systems on broadcast towers with spark gap arrestors, etc. a direct hit on a broadcast tower still blows equipment all to smithereens in the matching network shack at the base of the tower. As a ham, if you are going to run big towers and antennas (most common on 160 and lower) this is something you have to accept. You can't prevent damage in the event of a direct hit. Period. The best mitigation practice is to have your feeder(s) unhooked in the event of a direct hit, and even then that's no guarantee.
WA0CBW
Member
I have to agree with "prcguy" as I worked for Motorola for 40 years as both a contractor and a System Integration Engineer. In fact I was part of a group that was charged with writing much of the grounding and bonding requirements for the R56 document. Foremost was the National Electrical Code. The R56 manual however goes far beyond that. Building a site to R56 standards does not guarantee you will not take a lightning strike but it can greatly mitigate the damage.
The basic NEC rules are designed to provide a safe environment for yourself and your equipment especially in the area of potential voltage differences. I think "prcguy" explained it quite clearly what is required in terms of grounding and bonding your station and your equipment. Ignoring the requirements of section 800 can be dangerous to your personal safety.
Bill
The basic NEC rules are designed to provide a safe environment for yourself and your equipment especially in the area of potential voltage differences. I think "prcguy" explained it quite clearly what is required in terms of grounding and bonding your station and your equipment. Ignoring the requirements of section 800 can be dangerous to your personal safety.
Bill
The further the tower is from the equipment the more copper you need to bond the two areas together with low impedance. I have replaced repeater antennas that have taken direct hits and destroyed the antenna and there has been zero damage to any equipment in the budling. This is due to the massive grounding of the tower and building and the tower sits right next to the building. The mountain top repeater sites in my area at 3,00ft to past 10,000ft get hit all the time and I don't hear of any damage to equipment inside the buildings.
These are also not AM broadcast towers floating on insulators, they are grounded and only hold up various communication antennas. A tower 100ft out from the building or comm shelter is going to be difficult to protect compared to a tower right next to the building and bonded to the same ground ring.
AC9KH
Member
That's all lighning protection is about - mitigating the damage. There's no such thing as preventing damage from a direct hit on your station.
My earliest introduction to what lightning can do was when I was about 9 years old. A bolt struck one of our 90ft Madison concrete stave silos on the farm, which had a metal roof and silo chute. It blew the roof clean off the silo. The strike blew the telephone handset off the wall in the house, about 200 yards from ground zero. It also blew all the light bulbs in the barn. There was a 120V cord going to a ventilation fan that was hanging with a lower loop about 6" off the concrete floor. That cord arc'd to the concrete floor, which was damp, and burned it completely in two. And this was in a dairy barn that had everything bonded in it - stanchions and stall partitions, water lines, even the rebar in the concrete floor, to prevent "stray voltage" for cattle.
They used to say the "lightning travels in the wires". But at least in the case of the old party line phone in the house I think it was the EMF from the strike that caused a surge in the nearby phone lines, which used to be strung on telephone poles back in those days. Probably blew all the capacitors in the handset.
They claim lightning strikes the earth about 100 times per second someplace around the world, but witnessing its power firsthand is quite humbling.
AC9KH
Member
It's been quite a few years since we put up that tower for the wind turbine. I dug the hole for the foundation with my excavator. And I also dug the trenches for all the ground rods around it. IIRC they did not use wire to those ground rods. They are copper flat straps. Not braid, solid straps, but I don't remember the details of the connection to the ground rods. The tower is 7' 10" across at the base and there was a big copper plate under it that the straps are connected to.
I've always wondered, someday (maybe next summer) when I get a crane in here to get that dead turbine off the tower, how that would work as a ground plane for a AM broadcast-style antenna. I can get base insulators for it from Rohn, which would be fairly simple to install if I got a crane here to lift it. I tried shunt-feeding the tower once but that didn't work all that good.
There's a guy not too far from here that's got twin 200ft Rohn's, one is a 45G, the other is a 25G, for his ham station. One has base insulators on the columns and I need to go over there one of these days and check out what he did for the groundplane on that tower, see if it's significantly different from what I got.
On topic... kind of.... I'm not that familiar with separately derived neutrals....
I am familiar with bonding the ground ring around the tower to the earth electrode system for the rest of a facility with at least two ground wires (we always used 4/0).
Does a separately derived neutral effect the lightning protection requirements and the connections of the earth electrode system? and if so... How?
Thanks
Joel
I am familiar with bonding the ground ring around the tower to the earth electrode system for the rest of a facility with at least two ground wires (we always used 4/0).
Does a separately derived neutral effect the lightning protection requirements and the connections of the earth electrode system? and if so... How?
Thanks
Joel
