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Single ground
In almost 45 years of ham operation I have never bothered with a "good"
ground connection. I am in what might be my last location and now have a "real" tower (55' crank up). I understand the principles behind a single ground, or at least I think I do. However, ideal requirements (as often quoted in various codes and standards manuals) need to be matched with what one can actually do. I have several ground rods by the tower and one by the entry to my basement shack. The tower-to-entry-point has two #10 wires in the trench (but not not in the conduit) that connect the nearest of the tower ground rods to the entry-point rod. The distance is about 45'. From the entry point area to the rig is about 10' and has a single #10 wire. Also from the rig area to the electrical panel is another #10 wire that is about 40'. Is this a reasonable arrangement? Is it better than nothing? Worse than nothing? I will shortly place two ICE units at the entry point on the two coax lines from the tower. I am still considering what to do with the control lines --- there are 12 for a SteppIR, 6 for a rotator, and 6 for a remote coax switch. Bill W2WO |
"Bill Ogden" wrote I have several ground rods by the tower and one by the entry to my basement shack. The tower-to-entry-point has two #10 wires in the trench (but not not in the conduit) that connect the nearest of the tower ground rods to the entry-point rod. The distance is about 45'. From the entry point area to the rig is about 10' and has a single #10 wire. Also from the rig area to the electrical panel is another #10 wire that is about 40'. Is this a reasonable arrangement? Is it better than nothing? Worse than nothing? Hi Bill, it's reasonable and better than most, providing the following is also true: The coax shields grounded at the tower (min. at the bottom, best top and bottom), and again at the basement entrance single point ground. Shields must be grounded before connection to an arrestor. I will shortly place two ICE units at the entry point on the two coax lines from the tower. I am still considering what to do with the control lines --- there are 12 for a SteppIR, 6 for a rotator, and 6 for a remote coax switch. Bill W2WO ICE also makes protection for control lines. I have no experience with them in particular, but my six ICE coax arrestors have handled a lot of surge from several strikes less than 100' away, two of which were within 50' of antennas. I would also add that the importance of the bonding between shack single point ground and AC service entry point ground is critical to prevent ground potential rise (GPR) from a nearby strike's energy from going through your equipment via your own ground connections. The path in from ground and out through the back of your equipment AC power cords will always exist, but with proper bonding it will not be a destructive connection. Most stations have this station-ground to mains-ground bonding conductor outside the station, but I don't see the harm of having it inside either *if* it was a very short distance [yours is NOT SHORT]. The shorter the route for this bond the better, whatever path it may take. NEC requires it be less than 20'. Fat chance you say. Alternatives are to provide multiple ground rods along a 20' path of this critical bond. That means change your bonding conductor to run outside, from the station single point ground (rod), via a couple additional rods, to the AC mains service entry ground (rod). 73, Jack Painter Virginia Beach VA |
Bill,
I would reroute the wire from your electrical panel directly to the ground rod just outside your entry. Then from there run a single line to your rig. This keeps the rig out of the middle of the ground connections. If possible your AC line for the rig should run from where that ground rod is. AC protectors should be put at that point along with the coax protectors. Now you have a single point ground system and the rig is not in the middle of things. All grounds are at one point including all your protectors. As far as the control wires, get some large MOV's and place one on each line to ground. Again at your single ground point where your ground rod is at the entrance. With several control lines any surge energy that comes down them will be shared by all. You can get by without gas tubes in this situation as all those MOV's are effectively in parallel. If you look inside a rotator protector like Polyphaser makes that is all you will find in them. The ground connection from your protection devices to your ground rod should be as short and as large as you can manage. 3" wide copper strap if the distance is a few feet. If it is a little longer run place two copper straps edge to edge in parallel or a 6" strap. It is important to have a low resistance / low inductance path to your ground system. In addition you may want to add more ground rods / radials to your entrance ground. Even just buried radials run out in different directions away from that single ground rod that you have will help lots. Placing an additional ground rod at the end of each is still better. The big thing is to run the radials in different directions to get some space between your ground rods. Ideally the distance between rods should be the sum of their lengths. The ground saturates when trying to dissipate energy in one place. Spreading it out increases the amount of energy you can dump in a given amount of time. 73 Gary K4FMX On Thu, 18 Nov 2004 22:51:40 GMT, "Bill Ogden" wrote: In almost 45 years of ham operation I have never bothered with a "good" ground connection. I am in what might be my last location and now have a "real" tower (55' crank up). I understand the principles behind a single ground, or at least I think I do. However, ideal requirements (as often quoted in various codes and standards manuals) need to be matched with what one can actually do. I have several ground rods by the tower and one by the entry to my basement shack. The tower-to-entry-point has two #10 wires in the trench (but not not in the conduit) that connect the nearest of the tower ground rods to the entry-point rod. The distance is about 45'. From the entry point area to the rig is about 10' and has a single #10 wire. Also from the rig area to the electrical panel is another #10 wire that is about 40'. Is this a reasonable arrangement? Is it better than nothing? Worse than nothing? I will shortly place two ICE units at the entry point on the two coax lines from the tower. I am still considering what to do with the control lines --- there are 12 for a SteppIR, 6 for a rotator, and 6 for a remote coax switch. Bill W2WO |
"Jack Painter" wrote in message news:zbbnd.1127$wa1.571@lakeread04... snip The coax shields grounded at the tower (min. at the bottom, best top and bottom), and again at the basement entrance single point ground. Shields must be grounded before connection to an arrestor. Jack - regarding your comment on grounding the shields BEFORE connection to an arrestor: My arrestors are mounted on the common ground panel and the coax is grounded via the coax connector to those arrestors. What is the reason for a separate ground prior to that one. Maybe I misunderstood something, but it seems redundant to have a separate ground a few inches from that one. In response to another's comments regarding protection of the SteppIR, rotor, and other control lines: I use MOVs and .01 bypass caps on all those lines in a box at the base of the tower and have another set of the same at the entry panel box. Those components are mounted via European-style screw terminal strips (12 positions per strip) obtained from Jameco via the Web. Much cheaper than the same from Radio Shack or other sources. MOVs came from Mouser. A lightning strike last year entered my shack via relay control lines which were unprotected at that time. Hopefully, the new arrangement will help. 73, Floyd - K8AC |
This was answered off-line but for the group:
"Floyd Sense" wrote "Jack Painter" wrote in message snip The coax shields grounded at the tower (min. at the bottom, best top and bottom), and again at the basement entrance single point ground. Shields must be grounded before connection to an arrestor. Jack - regarding your comment on grounding the shields BEFORE connection to an arrestor: My arrestors are mounted on the common ground panel and the coax is grounded via the coax connector to those arrestors. What is the reason for a separate ground prior to that one. Maybe I misunderstood something, but it seems redundant to have a separate ground a few inches from that one. Coax shield grounding must be accomplished at the tower top, tower base (on ground level, not even 6" above!) and before the arrestor to comply with protector manufacturer requirements and to be in keeping with best engineering practices that are used nationwide in communication tower designs. The grounding just before the arrestor is for two purposes: 1. preventing unnecessary energy (whether capacitively or inductively coupled) from challenging the gas tube, MOV, coil (or all three) mechanisms of a protector, and 2: to help limit the differing potential available to reverse-path voltage from a nearby strike in ground potential rise conditions. A nearby strike can saturate the ground system, and a station ground can reference hundreds of thousands of volts 'up' from the ground, and 'out' via arrestors, phone, power cables to lower potential felt at some distant point. Grounding cable shield at the station single point ground thus helps maintain equipotential for both directions. Even if the station coax arrestors are mounted on the master ground the additional grounding is still helpful for voltage-division during saturated ground conditions. But in all cases that ground bus mount must never be the only place the coax shelding is grounded! In response to another's comments regarding protection of the SteppIR, rotor, and other control lines: I use MOVs and .01 bypass caps on all those lines in a box at the base of the tower and have another set of the same at the entry panel box. Those components are mounted via European-style screw terminal strips (12 positions per strip) obtained from Jameco via the Web. Much cheaper than the same from Radio Shack or other sources. MOVs came from Mouser. A lightning strike last year entered my shack via relay control lines which were unprotected at that time. Hopefully, the new arrangement will help. 73, Floyd - K8AC Several amateurs have reported successful use of private design MOV on control lines. While this could exceed commercially available equipment specs in some cases, for those less familiar with such designs, they are readily available in package-form to protect control lines. Jack |
On Fri, 19 Nov 2004 07:44:50 -0500, "Floyd Sense"
wrote: "Jack Painter" wrote in message news:zbbnd.1127$wa1.571@lakeread04... snip The coax shields grounded at the tower (min. at the bottom, best top and bottom), and again at the basement entrance single point ground. Shields must be grounded before connection to an arrestor. Jack - regarding your comment on grounding the shields BEFORE connection to an arrestor: My arrestors are mounted on the common ground panel and the coax is grounded via the coax connector to those arrestors. What is the reason for a separate ground prior to that one. Maybe I misunderstood something, but it seems redundant to have a separate ground a few inches from that one. In response to another's comments regarding protection of the SteppIR, rotor, and other control lines: I use MOVs and .01 bypass caps on all those lines in a box at the base of the tower and have another set of the same at the entry panel box. Those components are mounted via European-style screw terminal strips (12 positions per strip) obtained from Jameco via the Web. Much cheaper than the same from Radio Shack or other sources. MOVs came from Mouser. A lightning strike last year entered my shack via relay control lines which were unprotected at that time. Hopefully, the new arrangement will help. 73, Floyd - K8AC Floyd, The real reason for grounding the coax shield at the entrance panel in addition to having the protection device grounded is the voltage drop between the connector and the coax line. The cable to connector connection is usually not a good low resistance - high current joint as far as lightning is considered. During a lightning strike you may have considerable voltage drop across that junction. Sometimes connectors are found to have been welded to the cable or their threads welded due to lightning strikes because of the poor connection at the connector. Other times the junction may get burned open. It can also melt the solder quickly in a soldered on connector which would provide for an immediately poor connection. However, lots of people do not do the extra grounding of the cable at that point. Most are lucky if they get some sort of protection device installed and a ground connected. As Jack mentioned grounding the cable "at the bottom of the tower like is used nation wide in tower designs" is ideal. But unfortunately that is not how it usually gets done. Often the lines come off the tower at 6 to 10 feet above the ground to go to the building in a cable tray. But it would indeed be best if they were taken all the way to ground level before exiting the tower. The reason being that during a strike the tower and associated lines on it develop considerable voltage drop due to the high current being conducted. Coming off the tower above ground is like taping a resistor part way up from the ground end. Allowing more voltage to exit on the lines rather than the potential at the base of the tower where it is closer to ground. The tower usually has considerable inductance for voltage to develop across. Ideally lines should be grounded to the tower not only at the top and bottom but at distances along the tower length as well. This is to avoid flashovers that may puncture the line. Lightning protection schemes are all about voltage drop. Most due to inductance of the tower or other conductors carrying the current. All conductors will have inductance and resistance and therefore voltage drop if they are asked to carry lightning current. Keeping things out of the middle of that path is the trick. 73 Gary K4FMX |
Gary Schafer wrote in message . ..
On Fri, 19 Nov 2004 07:44:50 -0500, "Floyd Sense" As Jack mentioned grounding the cable "at the bottom of the tower like is used nation wide in tower designs" is ideal. But unfortunately that is not how it usually gets done. Often the lines come off the tower at 6 to 10 feet above the ground to go to the building in a cable tray. But it would indeed be best if they were taken all the way to ground level before exiting the tower. The reason being that during a strike the tower and associated lines on it develop considerable voltage drop due to the high current being conducted. Coming off the tower above ground is like taping a resistor part way up from the ground end. Allowing more voltage to exit on the lines rather than the potential at the base of the tower where it is closer to ground. The tower usually has considerable inductance for voltage to develop across. I'm one of those who pulls the coax off the tower at around eight feet and hangs it on a carrier wire from the tower to the outside wall near the shack. In the past I've had end insulators at both ends of the carrier wire. Your point about grounding the coax at the base of the tower is well taken but is obviously not possible in these situations. It occurs to me that the same effect can be accomplished by connecting a #6 or #8 solid wire between the the coax shields where they bend away from the tower and the base of the tower. Yes? Taking it a bit further it also occurs to me that the carrier wire could be connected to the base of the tower at the point where the tower connects to the ground rods there, then up the tower and connected to both the coax shields at the eight foot level and the tower again. Then horizontally to the house wall with the coax, then down to the ground rods just outside the shack to which the equipment is also grounded. I'd also connect the coax shields to the carrier wire again at the point where they turn away from the wire and go through the wall. One hefty continuous, unbroken length of copper wire. There would still be voltage differentials involved because there is no escape from the inductances BUT . . . is my thinking in the right direction here? 73 Gary K4FMX w3rv |
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Gary Schafer wrote in message . ..
On 20 Nov 2004 17:59:12 -0800, (Brian Kelly) wrote: .. . . I'm one of those who pulls the coax off the tower at around eight feet and hangs it on a carrier wire from the tower to the outside wall near the shack. Theref are many installations like yours in existance. It was the "common way" to do it some years ago. Not the best though. In the past I've had end insulators at both ends of the carrier wire. Your point about grounding the coax at the base of the tower is well taken but is obviously not possible in these situations. It occurs to me that the same effect can be accomplished by connecting a #6 or #8 solid wire between the the coax shields where they bend away from the tower and the base of the tower. Yes? No that won't do much good. If you ground the coax shield to the tower where it bends away from the tower you will have a much better (lower inductance) to ground with the tower than what the wire would provide. The wire would do almost no good at all when compared to the much larger tower in parallel. Got it. Taking it a bit further it also occurs to me that the carrier wire could be connected to the base of the tower at the point where the tower connects to the ground rods there, then up the tower and connected to both the coax shields at the eight foot level and the tower again. Same as above. Grounding the carrier to the tower will do much more than a wire to the ground rods at the tower. The carrier wire should not be insulated from the tower. It and the coax should both be grounded to the tower at the exit point. Otherwise you can have flashover's to the carrier. OK, cancel useless wire from base of tower. Then horizontally to the house wall with the coax, then down to the ground rods just outside the shack to which the equipment is also grounded. I'd also connect the coax shields to the carrier wire again at the point where they turn away from the wire and go through the wall. One hefty continuous, unbroken length of copper wire. There would still be voltage differentials involved because there is no escape from the inductances BUT . . . is my thinking in the right direction here? Connecting the carrier wire to the coax again at the house is a good idea for the same reason you should connect it at the tower. to prevent flashovers to the cables. The same situation exist on the tower itself with lines running down. That is why they should be grounded to the tower at several points. Especially on a tall tower. OK again. The tower has inductance just like any piece of wire has. Although the tower inductance is less than just a length of wire it still has inductance. When lightning strikes the top, the tower and lines all share the current to ground. The farther up from ground you are the higher the voltage will be with respect to ground. I got that from your prior post. It can be significant. Especially on a smaller tower. It took a few seconds to get your point but yes, it's a matter of how far up the tower the coax departs the tower as a percentage of the tower height. Since I'm planning a short (35-40 foot tubular crankup) tower I'll have both a "high inductance tower" and a high pulloff level in terms of percentage. Not good no matter how one looks at it. Leaving the tower only a few feet above ground with your coax line is putting that line at some point above ground that can have high voltage. The best way is to run the lines all the way to the bottom of the tower, ground them there, and then run underground to the house to your ground rods. Don't forget to also run a ground lead from your house ground to your tower ground system too. That's a given. Bury it along with the cables. That will give you more contact with the earth as well as tying the grounds together. The wire will be there but I doubt that I'll be able to bury it. The whole (small) property is part of a forest of huge old hardwoods several of which are crowded close to the house particularly along the wall thru which I need to feed the coax. You'd have to see it to believe it and it's only six miles from City Hall Philadelphia. Digging a trench is not possible thru the tangle of roots on any approach from the tower to the wall. I'm not looking forward to driving ground rods thru this maze of underground lumber but I'll do it even if it takes some serious power drilling to accomplish. What I could do is run all the cables to the bottom of the tower with shield bonds at the top of the moving section, another one at the top of the fixed section, another bond halfway down fixed section and the last one at the bottom of the tower. Which will also be surrounded by trees. There's a hole below the canopy big enough to accomodate a Hexbeam or some similar very compact HF antenna if I spot the tower correctly. Some contractor is going to have a really bad time digging the hole for tower base. From the base of the tower I'll run the cables and the carrier wire horizontally on the surface for a few feet then back up to the eight foot level to a tree trunk. Six feet would also work and the rest of the run would be per previous. The good news is that the soil is eternally damp highly conductive dark loam . . Gary K4FMX Thanks Gary. |
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