KA3SGM
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| The Science of Effective Grounding...
For both basic station performance, and lightning safety.
Having worked around enough commercial radio installations, I see the importance of effective grounding, and bonding everything metal, in addition to bonding all of the ground rods together, to eliminate differences in ground potential.
Let's open up some discussions of sensible, safe, and effective ground systems.
Let's share some thoughts, and try to prove or disprove some common grounding myths.
Something to think about off season, when Thunderstorms are at a minimum in the Northern Hemisphere, but high wind induced static charges on exposed metal objects(antennas, towers, ect..) due to cold and dry air might become more of a problem than you would think.
Not to mention the occasional and unexpected 'Thunder Snowstorms'.
Don't forget a good balanced RF ground too, for those with the mis-matched antennas, and a nice metal microphone that can give you a good RF shock to the unsuspecting mouth.
This from someone that has been attacked by my trusty old Astatic D-104 microphone more than a few times. OOOUCH!!
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burner50
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| When i put up an aerial mast I was planning on digging an 18 inch trench and sinking in Four 8' rods 18 inches apart and welding 8 gauge copper to them.
I've been told its overkill, but i've lost 3 computers and 2 tv's to lightning this year along with other major appliances. Been trying to get the electric company to put in a new ground, but they say since my service is underground it doesnt matter very much... Except the service goes aerial to underground 1 pole away from my house  |
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KA3SGM
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| said by burner50  :When i put up an aerial mast I was planning on digging an 18 inch trench and sinking in Four 8' rods 18 inches apart and welding 8 gauge copper to them. I've been told its overkill, but i've lost 3 computers and 2 tv's to lightning this year along with other major appliances. Been trying to get the electric company to put in a new ground, but they say since my service is underground it doesnt matter very much... Except the service goes aerial to underground 1 pole away from my house I believe the National Electrical Code specifies that individual ground rods be installed 6 feet apart, so a 6x6 square with 4 rods at the corners would be just the ticket.
I am also sold on #6 or larger copper for grounding, ideally a copper braid or strap, as it is far less likely to fuse 'open' under a high current strike.
Anyone else have a better idea??
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burner50
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1 edit | Guess i never consulted the NEC...
never heard of that either...
We put in a similar field at my last job except we used 24 rods, but this was for a freestanding structure not an aerial antenna.
Edit: A 15x15 structure with about 20 million worth of electronic equipment |
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KA3SGM
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| said by burner50 :Guess i never consulted the NEC... never heard of that either... We put in a similar field at my last job except we used 24 rods, but this was for a freestanding structure not an aerial antenna. Edit: A 15x15 structure with about 20 million worth of electronic equipment I think the NEC intent is that a 6 foot spacing between ground rods that are bonded together comprises two separate ground points.
Anything closer than 6 foot is obviously better than a single ground rod, but a cluster of closely spaced rods is considered a single ground point, the 6 foot spacing compensates for differential from one ground point to another.
Many commercial sites have several ground 'test wells' to determine the ground potential differential between different points at the same site.
Still, everything metal above ground is bonded to everything else, and all ground rods are bonded to each other.
This includes towers, buildings, antennas, feedlines, power and telco demarks, even the security fencing.
Everything metallic is connected to ground, and all ground points are bonded to each other.
Ideally, Lightning/Static/EMP flashes over the site uniformly, and finds an effective ground anywhere it touches.
At least that is the theory behind it, not that it always works that way.
Of course when you have 7 to 8 $ figures worth of electronics sitting on the ground, you do what you can to keep everything at an even ground potential, so nothing gets singled out to be 'THE' ground rod.
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Splitpair
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Cow Towne
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1 edit | reply to burner50
said by burner50 :When i put up an aerial mast I was planning on digging an 18 inch trench and sinking in Four 8' rods 18 inches apart and welding 8 gauge copper to them. Generally speaking your ground rods should not be closer to each other than the length of the rod. So with 8 foot rods 10 foot spacing would be fine.
If you are a really anal such as I am you will place a new ground rod at each service (power Telco cable satellite and antennas) in addition to a ground rod at each corner of the building. Those rods are bonded by a bare buried copper wire to form as close to a ring as possible to avoid dead-end-points.
Your minimum wire gauge for grounding and bonding should be #6 bare copper with all connections exothermically welded.
ALL building grounds shall be bonded together to prevent any possibility of a ground potential difference between grounds. Failing to do so is like begging ole mother nature to destroy your electronics.
A common grounding point should be established in the hut/shack and all cables as well as equipment shall be grounded to this point before connection to equipment.
When building your common grounding point don’t forget to insulate it from the wall to prevent any secondary paths to ground.
Where not placed by the service provider place primary surge protectors as close as possible to where the service enters the building but if possible always external to the building to minimize the chance of fire should a hard cross with power cause a catastrophic failure of the surge protector.
Don’t fail to include in the above an entire-home surge protector for the power entering the home. Be sure that protector provides hot to hot, hot to neutral and all lines to ground protection.
Contrary to common belief underground service is not immune to surges and lighting hits. The reality is at least around here that equipment connected to underground residential distribution (URD) is more susceptible to being damaged as FP&L’s engineers have decided that URD transformers don’t require primary surge protection as the primary is buried which is true. However they install streetlights which do get hit and carry that hit to the secondary which is in parallel to the service feeding the homes connected to the URD system.
At least in aerial residential distribution (ARD) the primary acts as a static line taking the hit and passing it to ground via. the primary surge protectors on the ARD transformers. Us folks on URD do not have that luxury.
I am currently (pardon the pun) in the process of re-writing this FAQ »AT&T Southeast Forum FAQ »How can I protect my DSL/dialup equipment from surges? to make it more relevant to Ham radio and will submit for inclusion to the FAQ’s here once completed. In the mean time I have included a couple PDF attachments from my employer on grounding and bonding. Just a little light reading to keep ya busy for now. 
Wayne
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KA3SGM
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| said by Splitpair : said by burner50 :When i put up an aerial mast I was planning on digging an 18 inch trench and sinking in Four 8' rods 18 inches apart and welding 8 gauge copper to them. Generally speaking your ground rods should not be closer to each other than the length of the rod. So with 8 foot rods 10 foot spacing would be fine. If you are a really anal such as I am you will place a new ground rod at each service (power Telco cable satellite and antennas) in addition to a ground rod at each corner of the building. Those rods are bonded by a bare buried copper wire to form as close to a ring as possible to avoid dead-end-points. Your minimum wire gauge for grounding and bonding should be #6 bare copper with all connections exothermically welded. ALL building grounds shall be bonded together to prevent any possibility of a ground potential difference between grounds. Failing to do so is like begging ole mother nature to destroy your electronics. A common grounding point should be established in the hut/shack and all cables as well as equipment shall be grounded to this point before connection to equipment. When building your common grounding point don’t forget to insulate it from the wall to prevent any secondary paths to ground. Where not placed by the service provider place primary surge protectors as close as possible to where the service enters the building but if possible always external to the building to minimize the chance of fire should a hard cross with power cause a catastrophic failure of the surge protector. Don’t fail to include in the above an entire-home surge protector for the power entering the home. Be sure that protector provides hot to hot, hot to neutral and all lines to ground protection. Contrary to common belief underground service is not immune to surges and lighting hits. The reality is at least around here that equipment connected to underground residential distribution (URD) is more susceptible to being damaged as FP&L’s engineers have decided that URD transformers don’t require primary surge protection as the primary is buried which is true. However they install streetlights which do get hit and carry that hit to the secondary which is in parallel to the service feeding the homes connected to the URD system. At least in aerial residential distribution (ARD) the primary acts as a static line taking the hit and passing it to ground via. the primary surge protectors on the ARD transformers. Us folks on URD do not have that luxury. I am currently (pardon the pun) in the process of re-writing this FAQ » AT&T Southeast Forum FAQ » How can I protect my DSL/dialup equipment from surges? to make it more relevant to Ham radio and will submit for inclusion to the FAQ’s here once completed. In the mean time I have included a couple PDF attachments from my employer on grounding and bonding. Just a little light reading to keep ya busy for now. Wayne AMEN Brother...Thanks !!
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Splitpair
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Cow Towne
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| reply to KA3SGM
said by KA3SGM :I think the NEC intent is that a 6 foot spacing between ground rods that are bonded together comprises two separate ground points. With widely spaced rods connected by the proper gauge bond wire an additional rod would halve the resistance under load of the first one a third rod would bring at all down to a third a fourth to a fourth and so on to the point of a diminishing return. However with close spacing such as 6 foot with average soil resistance/moisture the second rod will only lower the resistance under load by about 66% a third rod will make it 40% and the forth 33%.
To get a better understanding think of a ground rod as an antenna turned upside down and shoved into the earth. When passing power to earth the energy leaves the rod and spreads out in all directions from the rod producing a voltage gradient around the rod. If another bonded rod is too close its voltage gradient comes up against the other rods gradient reducing the effects of multiple rods.
The potential in volts per inch/foot varies by soil resistance and soil makeup. Generally speaking moist sandy soil will have the lowest resistance producing tight gradients and good protection.
Wayne
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Splitpair
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| reply to KA3SGM
said by KA3SGM :Let's share some thoughts, and try to prove or disprove some common grounding myths. Here’s a couple for ya.
Myth.
A ground system is costly I cannot afford such an expense.
Fact.
Unless you live in an apartment or a condo where the outside is not under your ownership or control you cannot afford not to have a good ground system.
Here’s a few money saving tips.
Think green as in your wallet. You will get a much better price on the copper part of the system down at Joes recycling than you will at Honest Abe’s Electrical Supply or the local Home Desperate. Most scrap yards around here sell copper at a 50% markup over what they paid which is better than half off the local supply houses and an even greater savings then the big box home DIY stores. You can get an even better deal if you buy insulated scrap and strip it yourself with a potato peeler. Remember you don’t need for the wire to be in a single length as you will be welding it at the ground rods so scraps work well.
Myth.
Exothermic welds are for the guys who “do it for a living” to save time. A good tight teardrop as all that is needed to connect a wire to a ground rod.
Fact.
A teardrop will come loose over time. What happens is the copper wire gradually deforms under pressure conforming to the shape of the rod and teardrop causing the connection to loose integrity.
If one insists on installing a teardrop either leave the top of the rod above ground so the connection can be inspected and whacked by the mower or place a sprinkler valve box over the ground rod so you will have access below the ground to re-torque the teardrop as needed. Of course once you have paid for a sprinkler valve box and a teardrop you will have exceeded the cost of a one-shot so technically you are pedaling backwards.
Wayne
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bilbo4fun
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I want to explain why a radio station engineer was on my case few years back. Not ham related but relevant. Tower-ground-radios. Their tower was on a huge hill, I was a new WISP. Wireless Internet provider. I could not attach to their tower due to it being hot, AM&FM. Engineer allowed me to erect a 44' tower next to their building. I did so, he inspected, measured and gave me go ahead to install radios on it and inside building. He did tell me I needed to ground the tower and radios and cables coming into building. I installed radios, Motorola cat5 lightning arrestors on tower and ran cables into building. Went to Electric supply place to buy clamps, wire etc. for grounding and cell phone rang. He was hot. Storm was coming and I didn't have grounding. When I got back to site he was their and watched me like a hawk. My point is I learned, tower then ground then radio. He was right and I learned something. Lightning can hit at anytime. I put the tower up. Radios, antennas, cables etc. on hand so did those, then went shopping for ground items. Tower then ground, guys. I have helped many hams erect towers prior to this and ground was the last thing done and should have been 2nd.
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KeysCapt
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This is a subject that is crucial to both safety and effective transmitting/receiving, and I'm very glad to see it started.
I'm still in the process of constructing my ground system, and it's voodoo science, in a lot of ways, at least to me. I've read volumes of information, and my own experience goes way back, but still I think grounding is a very complex topic.
In my case, I put an 8' ground rod in right at the foot of my antenna, and another right outside the 'shack', but haven't bonded those two together. I don't have a clue where FP&L installed their ground. I noticed that the guys who put the Satellite antenna on the house ran a nice ground to the GAS line! That used to be a big no-no, and I plan to drive another ground rod there, but it's on the other end of the house, so bonding them all would be a pretty big job.
Here's what I put together inside. Comments and criticisms welcome:
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dandeman
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Chapel Hill, NC
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1 edit | reply to KA3SGM
Thought I would post a few links related to lightning protection.
It can be hard for the average person to find the proper hardware to be used to build an effective lightning protection system.. For example, cable clamps specificly built for lightning system cabling connections have the 1 1/2" overlap and contact surface area, as opposed to standard NEC approved grounding clamps..
Here is a good catalog and with explanations on the use of the hardware.. »www.harger.com/products/grdcmp/g···/grc.cfm
The above link goes into their clamps section, but a look through their complete supply of products is worthwhile.
Most folks can't buy direct from Harger, but can buy Harger hardware from TESSCO.. »www.tessco.com
Another good source of lightning system materials.. »lightningrodstuff.com/index_file···0002.htm
Another source of information, which unfortunately does not seem to be available anymore was Polyphaser's publication "The Grounds for Lightning and EMP Protection". Invaluable document for designing a system.
I may be biased, but based on experience and what I see on commercial sites, I only entrust my equipment with Polyphaser. »www.polyphaser.com/ Have had modems blown up when using other brand protectors.. Haven't lost one yet with the Polyphasers.
It can be hard to find point of sales that carries especially the more custom purpose Polyphaser hardware, but DX Engineering is one of the better ones, i.e. carrying a broad range of their products and selling at reasonable prices.. »www.dxengineering.com/default.asp Between DX Engineering and TESSCO, I've been able to get everything I needed.
Theres another document I've found online detailing the lightning protection system design for commercial cellular and telephone system grounding (We work in that arena).. Will post the link if I can find it again..
I just recently upgraded my protection system at home after spending a bundle on a new HDTV system.. Briefly all protected hardware (communications, ham radio, video, etc.) are powered by a dedicated 1.4KW UPS and due to the distribution of the hardware over some distance in the house, I had to go to a perimeter ground system running the length of the house to protect against ground shifts..
There is a whole house AC protector at the service entrance, and AC, phone line, antenna surge suppressors at the appropriate points (all Polyphaser brand) tied to the perimeter ground system. Since I was able to get a hold of scrap 4/0 copper cable in the business, that's what I built the perimeter ground from.
We had a lightning strike only weeks later after I installed this system, that was strong enough to blow a 7200v/240v power distribution transformer and burn the underground telco trunk feeder open.. I'm on the same service, yet with everything connected and online there was no damage.. So it works! |
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KeysCapt
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| These sources are also mentioned in the FAQ:
»Amateur Radio »Grounding
I've found DX Engineering to be a great supplier, a site with some good technical info, and a retailer that is always willing to discuss your needs on the phone and help out with whatever you need.
Polyphaser also has some great technical stuff on their site:
»www.polyphaser.com/technical_notes.aspx |
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Splitpair
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Cow Towne | reply to KeysCapt
Hey KC I would loose the jumper from the Polyphaser and bolt it to the buss-bar.
Wayne
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Splitpair
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| reply to KeysCapt
said by KeysCapt :I don't have a clue where FP&L installed their ground. It's probably buried try checking right below the meter there should be a number 6 from the meter can to the ground rod. There might be a pipe coming out of the bottom of the meter can or the builder may have buried it under the plaster look for the pipe or lump in the wall to get you in the ball park.
I noticed that the guys who put the Satellite antenna on the house ran a nice ground to the GAS line! That used to be a big no-no, And it still is a gas meter may be bonded to a ground but it cannot be used as a ground.
and I plan to drive another ground rod there, but it's on the other end of the house, so bonding them all would be a pretty big job. I would. If you cannot easily make a trench then spade in the bond wire which is to take a spade push it into the ground and with a stick push the wire into the opening. Now this doesn’t get the wire to a code approved depth but you know where it is so just don’t cut it later.
Wayne
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dandeman
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Chapel Hill, NC
·AT&T Southeast
| reply to KeysCapt
Went out and took some pictures, primarily to illustrate some of the challenges I have had in building a properly designed system.. I always try to use UL listed and approved parts when doing ham radio power,UPS and grounding systems, but it can be difficult finding appropriate sized and cost materials (if it is even available) for a home installation versus some of much larger stuff we use on commercial (and very expensive) installations.. I've noticed that Polyphaser has even started putting statements on some of their equipment saying "not for household use", probably out of concern of improper installation.
Btw, if you subscribe to the NEC Digest (their quarterly magazine), they have had several articles indicating they are well aware of the fact that the code is behind in covering practices being used in a number of areas. The 2005 update added a section of photovoltaic (solar panels and associated hardware). The ham radio section has gotten pretty good.
Also there are some sections in NEC code that would be helpful to read, as already mentioned in grounding/bonding and also a couple of sections added in 2002 for standby UPS power (Art 702) and how to properly do cord and plug connected UPS system (Art 700.12E). Most of the UPS systems we install are hardwired connections, but we have done a couple of cord and plug connected systems feeding a protected branch circuit. Article 700.12E discusses this method..
So this post of focuses on some of the problem areas.
Clamps... the first photo above shows the usual clamps available (lower left side of photo) at the big box stores and electrical supply houses.. These are not big enough for the size cables needed in a lightning protection system and do not offer the contact surface area required..The clamp commonly used for grounding the #8 bare copper to a ground rod is actually listed for water pipe connections only.. Shown in the upper right are the Harger clamps that meet the requirement..
Another photo shows my ham radio antenna entrance with the Polyphasers and using the wrong clamps for the 4/0 cable underneath.. That's all I could find locally. I eventually found out about the Harger clamps and bought them through TESSCO.... Will put the right clamps on soon.
Another photo shows the whole house protector at the main distribution panel with the additional AWG #2 grounding cable tying the panel, suppressor into the perimeter ground. The old (but meeting NEC minimum requirement) AWG #8 copper is also shown. There is a NFPA document discussing lightning protection systems that I believe specifies these larger clamps, but do not have a copy of it yet..
Another pic is the copper bond plate at the HDTV (and at the furtherest point from the whole house UPS and Service entrance at the far end of the house. This point was of special concern since it could potentially expose the entire UPS protected AC supply (and all connected equipment) to a surge from the outside TV antenna. So another Polyphaser AC protector, rotor, protector, and antenna protector was mounted on a copper bond plate and is flat strapped to the permeter ground outside at the house foundation. Another pic shows the outside ground rod with the proper hardware for a flat strap connection.
This is still a work in progress....
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KeysCapt
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clubs: | Nice setup!
I especially like the copper sheeting used in place of round wire ... apparently the best method of choice. Did you place that copper backplate, or was that done by someone else? I like that too. |
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dandeman
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Chapel Hill, NC
·AT&T Southeast
1 edit | I did it all.. The copper plate is from Polyphaser minus the wood board they normally mount it on.. It was a left over from another project and decided to put it to good use..
Since it's up in the living room (and will be hidden behind a piece of furniture).. I polished and lacquer sprayed the copper, just so it would stay shiny and purdy  .
All the areas on the plate underneath the mounted proectors (making electrical connections) were masked off so the lacquer would not interfere..
Talk about guilding the lilly... |
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UHF
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One important thing I didn't see mentioned here (but it is possible I missed it)
NEVER let galvanized steel touch copper! And I always use the Harger 'goop' on all the connections. I don't remember what they call the stuff. |
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KeysCapt
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1 edit | Good points ... goop and dissimilar metals.
dandeman, thanks. I thought about that plate that DX Engineering sells, but now that I've seen it in your photo, I'll be getting one. Nice to have everything mounted to the same bonding base.
That's a nice setup, and you obviously did a lot of planning with it. |
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