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Station Grounding
i have a question.
in reference to station grounding, i have read keep the grounding strap as short as possible and not a multiple of a resonant length on the ham bands. with that in mind, even if i ground pieces of equipment to individual ground rods, won't the complete grounding system be long? in my mind i am looking around the room and seeing a grounding system being at least 12 feet long, if i go along the perimeter of the desks (which are in a "U" shape in the room. trying to grasp this in a practical sense. sorry if it is basic and i am just not understanding it. not responsible for spelling. :-) any input on this would be most appreciated. -- 73 de KU4YP "A clean ham shack is the Mike Prevatt sign of a sick mind....." Advanced Operator Bartow, Florida Active HF/VHF/Digital |
"ku4yp" wrote in reference to station grounding, i have read keep the grounding strap as short as possible and not a multiple of a resonant length on the ham bands. with that in mind, even if i ground pieces of equipment to individual ground rods, won't the complete grounding system be long? in my mind i am looking around the room and seeing a grounding system being at least 12 feet long, if i go along the perimeter of the desks (which are in a "U" shape in the room. trying to grasp this in a practical sense. sorry if it is basic and i am just not understanding it. Hi Mike. "Single Point ground"...this means *not* daisy-chaining to a bus bar behind equipment tables if possible, and connecting each piece of equipment to one (1) point that becomes the station's single point ground. *Not* several ground rods from "individual" equipment. After you collect all the station bonding straps at a single point, then you run to a very close ground rod. After you hit that first single ground rod with the bus from all station equipment, *then* you can branch out in a wide and plentiful ground field that bonds to all your antenna, towers, masts, and last but definitely not least, a direct low impedance and high current capable bond to the main AC service ground rod of your home. The RF portion of the ground can accomodate parallel connections to multiple ground rods in close to the station if necessary. They must be part of the lightning protection ground, never separate from it. There are tons of resources for this and lots of experts here in this group. You can also try this website I built just for those questions...one of the pages addresses RF grounds from the transmitter. http://members.cox.net/pc-usa/station/grounding.htm 73, Jack Virginia Beach |
Jack Painter wrote:
"Single Point ground"...this means *not* daisy-chaining to a bus bar behind equipment tables if possible, and connecting each piece of equipment to one (1) point that becomes the station's single point ground. *Not* several ground rods from "individual" equipment. After you collect all the station bonding straps at a single point, then you run to a very close ground rod. After you hit that first single ground rod with the bus from all station equipment, OK, I follow all that; but it doesn't fully address the original poster's question about ground routing inside the operating room. The question really is: what's the best *practical* way to route the grounding from that single exit point to all the individual pieces of equipment on the operating desks? Even a small amateur station can be spread over several feet of desk; L-shaped corner layouts are very common; and the OP is talking about an even larger U-shaped layout. This means the distances from individual items of equipment to the common the ground exit point can range from a few feet up to even a few tens of feet (in terms of the minimum practical distance around the rear of the desks). Also, modern amateur stations are heavily cross-connected by signal/data/control cables, which provide additional paths for damaging current surges to get inside the equipment. Everyone agrees (I hope) that the objective is to keep all the equipment at the same potential, even when the local ground potential "bounces" due to a nearby strike. Above all, the objective is to avoid current surges going through the insides of individual items - those are what do the damage. For all the practical reasons outlined above, I don't believe there is a completely "right" answer to the grounding problem inside the operating room. Every practical method seems to have some drawbacks. Based on your experience, what are your views about that specific problem, Jack? -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
"ku4yp" wrote
in reference to station grounding, i have read keep the grounding strap as short as possible and not a multiple of a resonant length on the ham bands. (etc) __________________ Unless your antenna requires an earth ground as an integral part of its design, the length or number of ham band wavelengths, or even the existence of a metallic path to earth is irrelevant to the radiation characteristics of the antenna itself. Still, a good earth ground and other means are desirable to protect your equipment from lightning transients, as developed by Jack Painter on his informative website link earlier in this thread. Here is a re-post of some earlier text I posted about the need for an "antenna ground." GW asked (clip): How do you determine the quality of an antenna ground at HF on an absolute basis? Not how well have I maximized what Mother Nature gave me at my QTH by adding radials, but how good is my ground compared to other stations' grounds at other locations? A low-resistance ground connection for a transmit antenna is important to the received signal level only when the antenna design requires it as a reference for its driven element, such as with the vertical radiators used in MW broadcasting. Most HF/VHF/UHF transmit antennas do not need, or use an earth ground for efficient radiation. As practical proof of this, recall that airborne antennas have no connection at all to earth ground, but still work just fine. And the transmit antennas used in commercial FM & TV broadcast are installed at the top of a tall tower, many wavelengths (and ohms) above earth potential. The tower is grounded for safety reasons, but the radiation patterns and received signal levels from those antennas would be the same even if that tower was not grounded. RF Visit http://rfry.org for FM broadcast RF system papers. |
'as short as possible' it the important phrase. its not always possible to
keep it really short. another important part is keeping it as fat as possible, meaning use heavy wire or, even better, something like copper flashing, aluminum flashing or angle stock, or something like that. aluminum angle stock that you find in 6-8' lengths in hardware stores makes excellent ground busses, its easily drilled for connections to equipment, can be easily bolted together at corners, and makes a nice neat installtion... use the 1" or wider stuff if you can get it. do not use multiple ground rods unless you also connect them all together outside... and if you do drive a 'station' ground rod be sure it is also connected outside with heavy conductor to your existing power entrance ground. and while you are at it make sure the power entrance is also connected to your water pipe coming in, pool filter ground, outdoor light ground, and anything else grounded outside the house. "ku4yp" wrote in message news:599_c.677$Va5.488@trnddc01... i have a question. in reference to station grounding, i have read keep the grounding strap as short as possible and not a multiple of a resonant length on the ham bands. with that in mind, even if i ground pieces of equipment to individual ground rods, won't the complete grounding system be long? in my mind i am looking around the room and seeing a grounding system being at least 12 feet long, if i go along the perimeter of the desks (which are in a "U" shape in the room. trying to grasp this in a practical sense. sorry if it is basic and i am just not understanding it. not responsible for spelling. :-) any input on this would be most appreciated. -- 73 de KU4YP "A clean ham shack is the Mike Prevatt sign of a sick mind....." Advanced Operator Bartow, Florida Active HF/VHF/Digital |
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"Richard Fry" Still, a good earth ground and other means are desirable to protect your equipment from lightning transients... Any 'Theory of Lightning' needs to be capable of including airplanes and their general success at lightning protection - obviously sans earth grounding. Typical airplanes get hits several times per year - often with no damage. 'Airplanes' is such an obvious one-word counter example to sooooooo many arguments about the "necessity" (sic) earth grounding... I'm glad you used the words "...and other means" and "desirable". You're not guilty. Personally, I believe that a Faraday Cage (with appropriate entrance protection) would be far more effective than fiddling with (optional) earth grounds. Since most commercial buildings are metal or equivalent, this gives the 'lightning professional' a huge advantage over the amateur (in his wooden house). Much of what works for 'professional' lightning protection works ~because~ the commercial installation is in a metal building. This point needs to be acknowledged by those professing their experience while advising the amateur in his wooden house full of lengthy, low voltage signal wires. Having 20,000 amps surging (uh oh - 'surge' - that'll trigger off the 'w_tom' idiobot - sorry) down the ground wire is obviously going to cause 'sparks' in adjacent wires and cables and 'minor' equipment damage - even with a perfect earth ground. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= *** Usenet.com - The #1 Usenet Newsgroup Service on The Planet! *** http://www.usenet.com Unlimited Download - 19 Seperate Servers - 90,000 groups - Uncensored -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= |
"Ian White, G3SEK" wrote Jack Painter wrote: "Single Point ground"...this means *not* daisy-chaining to a bus bar behind equipment tables if possible, and connecting each piece of equipment to one (1) point that becomes the station's single point ground. *Not* several ground rods from "individual" equipment. After you collect all the station bonding straps at a single point, then you run to a very close ground rod. After you hit that first single ground rod with the bus from all station equipment, OK, I follow all that; but it doesn't fully address the original poster's question about ground routing inside the operating room. The question really is: what's the best *practical* way to route the grounding from that single exit point to all the individual pieces of equipment on the operating desks? Even a small amateur station can be spread over several feet of desk; L-shaped corner layouts are very common; and the OP is talking about an even larger U-shaped layout. This means the distances from individual items of equipment to the common the ground exit point can range from a few feet up to even a few tens of feet (in terms of the minimum practical distance around the rear of the desks). Also, modern amateur stations are heavily cross-connected by signal/data/control cables, which provide additional paths for damaging current surges to get inside the equipment. Everyone agrees (I hope) that the objective is to keep all the equipment at the same potential, even when the local ground potential "bounces" due to a nearby strike. Above all, the objective is to avoid current surges going through the insides of individual items - those are what do the damage. For all the practical reasons outlined above, I don't believe there is a completely "right" answer to the grounding problem inside the operating room. Every practical method seems to have some drawbacks. Based on your experience, what are your views about that specific problem, Jack? -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek Right Ian, having equipment spread out over a wide area is an undesireable condition, but a reality for many operators. Running 3" wide or greater copper strapping in individual paths to one single bus "collector" is a challenge, but one worth trying. Equipment stacked or racked together could certainly be "grouped" and a common bonding strap run for each group to the SPG. But 20 linear feet of bus bar could have huge transient voltages developed across it from a nearby strike. As in a few hundred thousand volts between supposedly "grounded' equipment. Hence the importance of all equipment connecting to the same ground point, not via a long run of common bus bar to that ground point. Make your compromises according to your individual requirements and station layout. Just realize that in a nearby-by strike, lightning will find the weak points in any system and exploit that weakness to the fullest possibility. I experience numerous nearby strikes that probably raise the ground potential several hundred thousand volts, and expose my entire ground system to those voltages. If there were large potential differences between even bonded equipments in the station, deadly hazards would exist. It's all about choices, and we all have to make them. Best regards, Jack Painter Virginia Beach VA |
i thank you all for the comments.
to tie into the electirical service will be a pain as the electrical gound is on the total oposite end of the house from the shack. i'll have to work something out there. water pipe grounding will not be a problem. i can see i have much more reading to do. thanks agian, mike -- 73 de KU4YP "A clean ham shack is the Mike Prevatt sign of a sick mind....." Advanced Operator Bartow, Florida Active HF/VHF/Digital "Dave" wrote in message ... 'as short as possible' it the important phrase. its not always possible to keep it really short. another important part is keeping it as fat as possible, meaning use heavy wire or, even better, something like copper flashing, aluminum flashing or angle stock, or something like that. aluminum angle stock that you find in 6-8' lengths in hardware stores makes excellent ground busses, its easily drilled for connections to equipment, can be easily bolted together at corners, and makes a nice neat installtion... use the 1" or wider stuff if you can get it. do not use multiple ground rods unless you also connect them all together outside... and if you do drive a 'station' ground rod be sure it is also connected outside with heavy conductor to your existing power entrance ground. and while you are at it make sure the power entrance is also connected to your water pipe coming in, pool filter ground, outdoor light ground, and anything else grounded outside the house. "ku4yp" wrote in message news:599_c.677$Va5.488@trnddc01... i have a question. in reference to station grounding, i have read keep the grounding strap as short as possible and not a multiple of a resonant length on the ham bands. with that in mind, even if i ground pieces of equipment to individual ground rods, won't the complete grounding system be long? in my mind i am looking around the room and seeing a grounding system being at least 12 feet long, if i go along the perimeter of the desks (which are in a "U" shape in the room. trying to grasp this in a practical sense. sorry if it is basic and i am just not understanding it. not responsible for spelling. :-) any input on this would be most appreciated. -- 73 de KU4YP "A clean ham shack is the Mike Prevatt sign of a sick mind....." Advanced Operator Bartow, Florida Active HF/VHF/Digital |
ku4yp wrote:
i have a question. in reference to station grounding, i have read keep the grounding strap as short as possible and not a multiple of a resonant length on the ham bands. with that in mind, even if i ground pieces of equipment to individual ground rods, won't the complete grounding system be long? in my mind i am looking around the room and seeing a grounding system being at least 12 feet long, if i go along the perimeter of the desks (which are in a "U" shape in the room. W1MCE replies: I have used a 1/2 inch copper pipe mounted along the back edge of the table[s] holding my station equipment. The case of each piece of equipment is connected directly to the copper pipe using 1 inch braided strap about 6 to 12 inches long depending on equipment size. This pipe provides an equipotential plane for all my equipment. [Another method would be to install a thin copper sheath on top of your desk/tables and connect directly to it for the equipotential plane.] Now, how to connect the equipotential plane to brown dirt [earth] is the next issue. You are correct that it is desirable to keep this 'non-resonant' on the bands you operate. There are two issues here that need to be addressed. First, if you are close to the earth ground then a simple #6 AWG wire to a ground rod is adequate. Second, if you are higher than 1/4 wavelength at the highest frequency of interest use two #6 AWG wires OF DIFFERENT LENGTHS, not harmonically related, connected to the ground rod. The different lengths assure that the equivalent connection is NOT RESONANT. In very fortunate cases an additional station ground is not required! Believe it or not! ... My station is located on the ground floor in the family [my] TV room right under the electrical distribution panel. My 120 VAC line comes directly from the service entrance through about 3 feet of wire. The 240 VAC for my amplifier comes directly from the service entrance through 4 feet of wire. The service box is 'earthed' by a NEC compliant connection. My connections to the service box are therefore very short. A major point of caution is required. The NEC requires ONLY ONE ground connection. Multiple ground connections introduce VERY SERIOUS ground loops that may violate the NEC criteria. This opens a VERY LARGE loop hole in your home owner's insurance policy. If you are adding a second earth [ground] connection at your station use an isolation transformer to break up the ground loops in the basic 120 VAC connection. Consult with an electrician regarding your local and NEC codes. It is noted that station grounding and antenna counterpoise construction are two different things. I am not addressing the counterpoise issue. |
Dave Shrader wrote:
. . . A major point of caution is required. The NEC requires ONLY ONE ground connection. Multiple ground connections introduce VERY SERIOUS ground loops that may violate the NEC criteria. This opens a VERY LARGE loop hole in your home owner's insurance policy. If you are adding a second earth [ground] connection at your station use an isolation transformer to break up the ground loops in the basic 120 VAC connection. Consult with an electrician regarding your local and NEC codes. . . . My NEC book is getting pretty old now, 1990, but at that time, multiple grounds were often not only permitted, but required. And a *minimum* spacing was sometimes specified. For example, section 250-84, Resistance of Made Electrodes: "A single electrode consisting of a rod, pipe, or plate which does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified in Sections 250-81 or 250-83. Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall be not less than 6 feet (1.83m) apart." Or section 250-81(a), Metal Underground Water Pipe: ". . .A metal underground water pipe shall be supplemented by an additional electrode of a type specified in Section 250-81 or in Section 250-83. The supplemental electrode shall be permitted to be bonded to the grounding electrode conductor, the grounded service-entrance conductor, the grounded service raceway, any grounded sevice enclosure, or the interior metal water piping at any convenient point." When I replaced the service (in 1979) in my 1952 house, the system ground was a water pipe connection and I was required to add a ground rod. Neither was considered adequate in itself; both were required by the code at that time. I agree wholeheartedly about consulting an electrician. Non-electricians (including me) often have mistaken ideas about the content of the NEC. It doesn't hurt to have an up to date copy of the NEC for reference, either, if you anticipate doing any of the work yourself. Roy Lewallen, W7EL |
"Roy Lewallen" wrote Dave Shrader wrote: . . . A major point of caution is required. The NEC requires ONLY ONE ground connection. Multiple ground connections introduce VERY SERIOUS ground loops that may violate the NEC criteria. This opens a VERY LARGE loop hole in your home owner's insurance policy. If you are adding a second earth [ground] connection at your station use an isolation transformer to break up the ground loops in the basic 120 VAC connection. Consult with an electrician regarding your local and NEC codes. . . . My NEC book is getting pretty old now, 1990, but at that time, multiple grounds were often not only permitted, but required. And a *minimum* spacing was sometimes specified. Outdated only regarding water pipe Roy, but good advice. And Dave's above interpretation of NEC is a misunderstanding of the subject - easy to do so consult a professional if you have any douvbt whatsoever about what your are doing. Isolation transformers are not an option for isolating a station ground from AC service entrance. They are permitted only in lmited cases where independent grounding is required, and in other cases where HV isolating transformers or fiber optic isolate feedlines. No one in this group will likely have that requirement, so put that out of your mind Dave. You *MUST* bond your station ground to the AC service main ground. Ignore this at the peril of your entire system, which had better be 100% isolated from all power and external feedlines and grounds. That is an option for protection, isolating from *everything*. But it means unplugging and shorting to ground all feedlines, disconnecting and removing RF ground connections, disconnecting computer modems, telephone, and AC power to all of your connected equipment. A really poor option in my opinion, because if you forget something, or risk your life trying to disconnect during a surprise thunderstorm, what was it worth? For example, section 250-84, Resistance of Made Electrodes: "A single electrode consisting of a rod, pipe, or plate which does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified in Sections 250-81 or 250-83. Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall be not less than 6 feet (1.83m) apart." Or section 250-81(a), Metal Underground Water Pipe: ". . .A metal underground water pipe shall be supplemented by an additional electrode of a type specified in Section 250-81 or in Section 250-83. The supplemental electrode shall be permitted to be bonded to the grounding electrode conductor, the grounded service-entrance conductor, the grounded service raceway, any grounded sevice enclosure, or the interior metal water piping at any convenient point." When I replaced the service (in 1979) in my 1952 house, the system ground was a water pipe connection and I was required to add a ground rod. Neither was considered adequate in itself; both were required by the code at that time. I agree wholeheartedly about consulting an electrician. Non-electricians (including me) often have mistaken ideas about the content of the NEC. It doesn't hurt to have an up to date copy of the NEC for reference, either, if you anticipate doing any of the work yourself. Roy Lewallen, W7EL Jack Painter Virginia Beach VA |
Roy Lewallen wrote:
Dave Shrader wrote: . . . A major point of caution is required. The NEC requires ONLY ONE ground connection. Multiple ground connections introduce VERY SERIOUS ground loops that may violate the NEC criteria. This opens a VERY LARGE loop hole in your home owner's insurance policy. If you are adding a second earth [ground] connection at your station use an isolation transformer to break up the ground loops in the basic 120 VAC connection. Consult with an electrician regarding your local and NEC codes. . . . My NEC book is getting pretty old now, 1990, but at that time, multiple grounds were often not only permitted, but required. And a *minimum* spacing was sometimes specified. For example, section 250-84, Resistance of Made Electrodes: "A single electrode consisting of a rod, pipe, or plate which does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified in Sections 250-81 or 250-83. Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall be not less than 6 (1.83m) apart." Is it something like this? Multiple ground rods are permitted (encouraged, even) in order to establish one good ground connection; but the wiring system can have only one ground connection. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Jack Painter wrote:
Right Ian, having equipment spread out over a wide area is an undesireable condition, but a reality for many operators. Running 3" wide or greater copper strapping in individual paths to one single bus "collector" is a challenge, but one worth trying. Equipment stacked or racked together could certainly be "grouped" and a common bonding strap run for each group to the SPG. But 20 linear feet of bus bar could have huge transient voltages developed across it from a nearby strike. As in a few hundred thousand volts between supposedly "grounded' equipment. Hence the importance of all equipment connecting to the same ground point, not via a long run of common bus bar to that ground point. Make your compromises according to your individual requirements and station layout. Thanks very much for those thoughts, Jack. As I'd guessed, you had some good suggestions, but you can see their practical problems too. The same applies to an alternative method, which is to group related items of equipment as closely as possible, and connect them by the shortest possible straps to a large sheet of metal. The key feature is that this sheet should be *very wide*, to create a very low inductance and help minimize any voltage drops along its length. Conductor thickness doesn't matter in this location, so a sheet of copper-clad PC board is fine. It's also very easy to solder short grounding straps onto the PC board, and move them around without having to disconnect the whole sheet to drill it. Some people put the sheet on the table, and the gear on top of the sheet. If there is a shelf carrying another level of equipment above, another practical way is to fasten the sheet to the underside of the shelf. The reason why conductor thickness doesn't matter in this location is that we don't expect full-bore lightning surges through the station itself. The ground bonding at the common service entrance should have diverted the main surge safely to ground, so the equipment bonding inside the station should only need to deal with very much smaller currents - smaller, but still large enough to damage sensitive electronics. Also, the higher-frequency components of the surge will only run along the surface anyway, so what matters most is width and surface area rather than thickness of copper. As Jack says, busbars are a particular invitation to develop voltage drops along their length. This "ground-sheet" system accepts there will be some voltage drop along its length, but does everything practicable to minimize it. A wide sheet is vastly better than busbars, and solid copper busbars are a particular waste of money - a large sheet of scrap PC board will do it far better, for almost nothing. If I had the luxury of a large station, I'd use these sheets as part of a wider-scale "grouping" system, as Jack suggests. Just realize that in a nearby-by strike, lightning will find the weak points in any system and exploit that weakness to the fullest possibility. In this climate, lightning is actually quite a minor hazard. What has driven me to organize and bond equipment together is the need to control RFI due to ground currents (of which I generate rather a lot). What's good for the one is generally good for the other... and often good for received noise reduction too. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Ian White, G3SEK wrote: Roy Lewallen wrote: My NEC book is getting pretty old now, 1990, but at that time, multiple grounds were often not only permitted, but required. And a *minimum* spacing was sometimes specified. For example, section 250-84, Resistance of Made Electrodes: "A single electrode consisting of a rod, pipe, or plate which does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified in Sections 250-81 or 250-83. Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall be not less than 6 (1.83m) apart." Is it something like this? Multiple ground rods are permitted (encouraged, even) in order to establish one good ground connection; but the wiring system can have only one ground connection. Well, yes and no. As I read it, all the ground electrodes have to be connected to the service box, as they are at my house. I have a water-pipe ground and a ground rod; they're physically widely separated, and each has its own conductor going back to the service box. So I guess you could call the service box a single "ground connection". The neutral and safety ground conductors of each circuit are individually grounded at the service box also, giving further support to interpreting its function as a single ground connection. A number of ground methods and devices are approved, such as buried rods or plates, concrete grounds, or (in my old code book anyway), water pipe ground. Some can be used alone and others need a second ground device as a supplement. When multiple ground rods are used, the code has requirements for bonding them to each other. Roy Lewallen, W7EL |
"Roy Lewallen" wrote in message ... Ian White, G3SEK wrote: Roy Lewallen wrote: My NEC book is getting pretty old now, 1990, but at that time, multiple grounds were often not only permitted, but required. And a *minimum* spacing was sometimes specified. For example, section 250-84, Resistance of Made Electrodes: "A single electrode consisting of a rod, pipe, or plate which does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified in Sections 250-81 or 250-83. Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall be not less than 6 (1.83m) apart." Is it something like this? Multiple ground rods are permitted (encouraged, even) in order to establish one good ground connection; but the wiring system can have only one ground connection. Well, yes and no. As I read it, all the ground electrodes have to be connected to the service box, as they are at my house. I have a water-pipe ground and a ground rod; they're physically widely separated, and each has its own conductor going back to the service box. So I guess you could call the service box a single "ground connection". The neutral and safety ground conductors of each circuit are individually grounded at the service box also, giving further support to interpreting its function as a single ground connection. A number of ground methods and devices are approved, such as buried rods or plates, concrete grounds, or (in my old code book anyway), water pipe ground. Some can be used alone and others need a second ground device as a supplement. When multiple ground rods are used, the code has requirements for bonding them to each other. Roy Lewallen, W7EL Using a cold water pipe is a bad idea and is not allowed by some local codes even though it may be allowed by the national code. This is partly because it should only be connected to the ground system at one point and it is too easy to connect it at more than one. Also there is the possible interaction with gas lines and plumbers and home owners sometimes modify plumbing in ways that make them poor grounds.. |
Jimmy wrote:
"Using a cold water pipe is a bad idea and is not allowed by some local codes even though it may be allowed by the national code." You don`t want to be electrocuted when holding an electric appliance and a cold water valve simultaneously. My electric company, the former Houston Lighting and Power Company, writes: "All services shall be properly grounded. Note - NEC requires grounding to a "metallic underground water piping system" if available. Acceptable alternatives include a driven ground rod which is preferred by HL&P Co. regardless of the type grounding electrode used. NEC requires that the "interior cold water pipimg system" be bonded to it." Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote:
My electric company, the former Houston Lighting and Power Company, writes: "All services shall be properly grounded. Note - NEC requires grounding to a "metallic underground water piping system" if available. Acceptable alternatives include a driven ground rod which is preferred by HL&P Co. regardless of the type grounding electrode used. NEC requires that the "interior cold water pipimg system" be bonded to it." That last point is the same in the UK. Gas and water supplies are never relied on to provide an electrical ground, but they must be bonded to the electrical supply ground. Additional local bonding is also required for all metalwork in bathrooms and shower rooms. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
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On Sat, 04 Sep 2004 20:28:58 GMT, "ku4yp" wrote:
i thank you all for the comments. to tie into the electirical service will be a pain as the electrical gound is on the total oposite end of the house from the shack. i'll have to work something out there. water pipe grounding will not be a problem. i can see i have much more reading to do. thanks agian, mike When we had an electrician upgrade the incoming electrical service box on my mother's house (circa 1960), he ran a large 8 gauge wire from the box at the end of the garage, along the wall of the house all the way to the incoming water line from the street near the other end of the basement, where he tied it to ground next to the water meter. The National Electrical Code has changed, and those in older houses might consider upgrading to current code (no pun intended) even if not actually required. In industrial situations, I have had to deal with ground loop problems, which are a PITA to find. Do your grounding correctly, and you will be safer, and have an easier time of it. Happy trails, Gary (net.yogi.bear) ------------------------------------------------ at the 51st percentile of ursine intelligence Gary D. Schwartz, Needham, MA, USA Please reply to: garyDOTschwartzATpoboxDOTcom |
On Thu, 09 Sep 2004 15:10:28 GMT, Gary S. Idontwantspam@net wrote:
[snip] |In industrial situations, I have had to deal with ground loop |problems, which are a PITA to find. Do your grounding correctly, and |you will be safer, and have an easier time of it. You should have seen the problems I had when I had the house electricians wiring up an r-f shielded room. Trying to convince them that they had to run just *one* ground wire from a single point on the room to a building ground and not the service entrance ground *and* that the wire couldn't be bare and laying on the sprinkler system piping, the A/C ducts and electrical conduit in the overhead. Then fighting off the fire department guys that insisted that they were going to run a pipe into the room for sprinklers. |
On Thu, 09 Sep 2004 08:41:17 -0700, Wes Stewart
wrote: On Thu, 09 Sep 2004 15:10:28 GMT, Gary S. Idontwantspam@net wrote: [snip] |In industrial situations, I have had to deal with ground loop |problems, which are a PITA to find. Do your grounding correctly, and |you will be safer, and have an easier time of it. You should have seen the problems I had when I had the house electricians wiring up an r-f shielded room. Trying to convince them that they had to run just *one* ground wire from a single point on the room to a building ground and not the service entrance ground *and* that the wire couldn't be bare and laying on the sprinkler system piping, the A/C ducts and electrical conduit in the overhead. Then fighting off the fire department guys that insisted that they were going to run a pipe into the room for sprinklers. Most licensed electricians (in theory all of them, but I'll leave that) have a good understanding of issues related to DC and 60 Hz AC, voltages up to 480, currents up to 100 A. Once you get to higher frequencies, including RF, or to serious voltages or currents, the number of people who really understand drops off rather quickly, unfortunately as the potential problems and dangers increase. Happy trails, Gary (net.yogi.bear) ------------------------------------------------ at the 51st percentile of ursine intelligence Gary D. Schwartz, Needham, MA, USA Please reply to: garyDOTschwartzATpoboxDOTcom |
On Thu, 09 Sep 2004 08:41:17 -0700, Wes Stewart wrote:
On Thu, 09 Sep 2004 15:10:28 GMT, Gary S. Idontwantspam@net wrote: [snip] |In industrial situations, I have had to deal with ground loop |problems, which are a PITA to find. Do your grounding correctly, and |you will be safer, and have an easier time of it. You should have seen the problems I had when I had the house electricians wiring up an r-f shielded room. Trying to convince them that they had to run just *one* ground wire from a single point on the room to a building ground and not the service entrance ground *and* that the wire couldn't be bare and laying on the sprinkler system piping, the A/C ducts and electrical conduit in the overhead. Then fighting off the fire department guys that insisted that they were going to run a pipe into the room for sprinklers. Apparently the electricians only knowledge of 'loop' was in 'loophole'. |
Jimmie wrote:
Should re read what I write sometimes. I was refering to using the water pipe as the sole ground for your electrical system. This used to be a common thing and pemissable by the NEC, not sure if it still is. When I replaced my service in 1975, a water pipe ground (which is all my 1952 house had) wasn't sufficient to satisfy the NEC, so I had to add a ground rod. So the NEC hasn't permitted a water pipe ground as the sole ground for at least 29 years. It apparently was permissible in 1952. Roy Lewallen, W7EL |
So the NEC hasn't permitted a water pipe ground as the sole
ground for at least 29 years. Roy Lewallen, W7EL ===================================== A good thing too. At any time a fully qualified plumber can come along and replace a section of metal water pipe with polyethelene, one of the best insulating materials known to science. |
I am not very familiar with USA power-grounding regulations and they
probably vary from state to state. But I am under the impression that in some simple circumstances, perhaps domestic, a single ground rod is considered adequate for safety purposes. Under similar circumstances a maximum ground electrode resistance ( whatever its construction ) of 50 ohms is specified. A 'standard' ground rod is 8 feet long and 1 inch in diameter. An average soil resistivity is 500 ohm-metres ( = 2 mS ). See Eznec? The calculated resistance of a single standard rod in average soil is 194 ohms. ( I'm sure the calculating formula can be found somewhere on the IEEE shelves. There ought to be greater use made of it. ) Now I don't expect the alarm bells to be rung from Washington to LA. But isn't there a serious inconsistency somewhere? As a matter of interest, the resistances to ground of 2, 3 and 4 rods in parallel, spaced 6 feet apart in average soil, are as follows - 2 Rods = 113 ohms 3 Rods = 86 ohms 4 Rods = 70 ohms all of which exceed the specified maximum of 50 ohms. Quite a low average soil resistivity of about 130 ohms is needed to bring 50 percent of installations within specification. If my starting data is wildly adrift then disregard my waffle. ---- Reg, G4FGQ |
yeah, and its worse than that. most times they only use 1/2" or 5/8"
diameter rods, and the 6' spacing becomes 3' 'or so' when they do more than one, which seems to be getting more common. the last electrician i hired actually put 2 rods at a separate garage service entrance without being prompted.... but maybe it was all the towers and other rods around that convinced him he should do it right before i said anything. "Reg Edwards" wrote in message ... I am not very familiar with USA power-grounding regulations and they probably vary from state to state. But I am under the impression that in some simple circumstances, perhaps domestic, a single ground rod is considered adequate for safety purposes. Under similar circumstances a maximum ground electrode resistance ( whatever its construction ) of 50 ohms is specified. A 'standard' ground rod is 8 feet long and 1 inch in diameter. An average soil resistivity is 500 ohm-metres ( = 2 mS ). See Eznec? The calculated resistance of a single standard rod in average soil is 194 ohms. ( I'm sure the calculating formula can be found somewhere on the IEEE shelves. There ought to be greater use made of it. ) Now I don't expect the alarm bells to be rung from Washington to LA. But isn't there a serious inconsistency somewhere? As a matter of interest, the resistances to ground of 2, 3 and 4 rods in parallel, spaced 6 feet apart in average soil, are as follows - 2 Rods = 113 ohms 3 Rods = 86 ohms 4 Rods = 70 ohms all of which exceed the specified maximum of 50 ohms. Quite a low average soil resistivity of about 130 ohms is needed to bring 50 percent of installations within specification. If my starting data is wildly adrift then disregard my waffle. ---- Reg, G4FGQ |
Roy Lewallen wrote:
Jimmie wrote: Should re read what I write sometimes. I was refering to using the water pipe as the sole ground for your electrical system. This used to be a common thing and pemissable by the NEC, not sure if it still is. When I replaced my service in 1975, a water pipe ground (which is all my 1952 house had) wasn't sufficient to satisfy the NEC, so I had to add a ground rod. So the NEC hasn't permitted a water pipe ground as the sole ground for at least 29 years. It apparently was permissible in 1952. Roy Lewallen, W7EL And I had a friend, had home in Springfield Or., was built during the WAR! Home was plummed with (If you can believe this) Electrical Conduit! Apparently, because of the shortage of materials, this met code then! Stuff finally rotted out, around 1971-- remember him useing his vacation to replum the house! And I had one , in K.Falls, OR was built as old farm house, with steel pipe, that started leaking- electrolysis was rapidly eating it- replaced with Copper. Was curious about the UNIONS used on it-- turns out that those are INSULATED JOINTS! Plumber said had Copper pipes eating out in as little as 3-5 years, before they were available, with them expected 25-30 years, before the pipe gives out! As running current thru a pipe with an insulated connection is worthless as a ground, and even current flowing thru a copper pipe, is hazardious to its health, don't think would recommend this tactic if you want a good ground. Jim NN7K |
On Thu, 09 Sep 2004 17:04:08 GMT, Walter Maxwell wrote:
|On Thu, 09 Sep 2004 08:41:17 -0700, Wes Stewart wrote: | |On Thu, 09 Sep 2004 15:10:28 GMT, Gary S. Idontwantspam@net wrote: |[snip] ||In industrial situations, I have had to deal with ground loop ||problems, which are a PITA to find. Do your grounding correctly, and ||you will be safer, and have an easier time of it. | |You should have seen the problems I had when I had the house |electricians wiring up an r-f shielded room. Trying to convince them |that they had to run just *one* ground wire from a single point on the |room to a building ground and not the service entrance ground *and* |that the wire couldn't be bare and laying on the sprinkler system |piping, the A/C ducts and electrical conduit in the overhead. | |Then fighting off the fire department guys that insisted that they |were going to run a pipe into the room for sprinklers. | |Apparently the electricians only knowledge of 'loop' was in 'loophole'. Yep. To elaborate. The building (100,000 sq ft) was constructed of tip-up concrete exterior walls and steel columns and roof trusses. A few of the columns, were dedicated ground points, complete with copper plates for wire attachement. They were bonded to the steel rebar grid in the concrete slab-on-grade floor. All of the A/C conductors into the room, neutral included, ran through some real hefty line filters that were on the outside of the room with feedthrus into a distribution box inside. On top of the room was a single copper stud for ground connection. As I said earlier, the electricians wanted to ground the room with the usual A/C distribution safety ground wire. When I said no, they needed to go to the nearest column ground, they ran a 6 AWG bare copper wire to the grounding plate. Of course the wire was in contact with everything it contacted. So when I saw this I said no, you have to run an insulated wire. So the next iteration was a single green wire. I said no, some bozo plumber (I shouldn't say this, my brother's a plumber) or HVAC guy will be up there working and the wire will be in the way and they'll cut it and my room with be a 100 or so V above ground due to all of the capacitors in the filters. I finally got my insulated wire in conduit. Then the HVAC guys wanted to run a steel duct to the room. Noooo, use an insulated collar and give me a pneumatic thermostat. Then as mentioned earlier, it was the fire department. They saw all of the handy pipes running through my feedthru panel (actually waveguide below cutoff feedthrus) and said we can just plumb in the water through one of these. Nooo, can't have a metallic connection. So they say, they can use a dielectric union. Nooo, the water in those pipes hasn't moved in 20 years and is primarily rust. When they started talking about halon I said that my widow was going to have a real good time with the millions she would get from the lawsuit. They decided that the regular sprinkler system above the shielded room was okay afterall. |
"Reg Edwards" wrote I am not very familiar with USA power-grounding regulations and they probably vary from state to state. But I am under the impression that in some simple circumstances, perhaps domestic, a single ground rod is considered adequate for safety purposes. Under similar circumstances a maximum ground electrode resistance ( whatever its construction ) of 50 ohms is specified. A 'standard' ground rod is 8 feet long and 1 inch in diameter. An average soil resistivity is 500 ohm-metres ( = 2 mS ). See Eznec? The calculated resistance of a single standard rod in average soil is 194 ohms. ( I'm sure the calculating formula can be found somewhere on the IEEE shelves. There ought to be greater use made of it. ) Now I don't expect the alarm bells to be rung from Washington to LA. But isn't there a serious inconsistency somewhere? As a matter of interest, the resistances to ground of 2, 3 and 4 rods in parallel, spaced 6 feet apart in average soil, are as follows - 2 Rods = 113 ohms 3 Rods = 86 ohms 4 Rods = 70 ohms all of which exceed the specified maximum of 50 ohms. Quite a low average soil resistivity of about 130 ohms is needed to bring 50 percent of installations within specification. If my starting data is wildly adrift then disregard my waffle. ---- Reg, G4FGQ Yes Reg, sorry the figures are (thankfully) in error. Especially since 25ohm is required by our U.S. NEC, and that's easily attained in some soils, not so easy in others. This is being changed in the 2004 code changes, but it was paraphrased below: The NEC does not specify a maximum earth resistance for the grounding electrode system required under Article 250-81. The only place that does specify earth resistance is under Article 250-84, for "made" (rod, pipe, and plate) electrodes. Here the NEC specifies a resistance to ground of 25 Ohms or less for a single electrode. If the electrode does not meet 25 Ohms, it must be supplemented by one additional electrode. However the combination of the two electrodes does not have to meet the 25 ohm requirement! http://www.cpccorp.com/deep.htm Neither should anyone be overly concerned with acheiving low DC-resistivity of a grounded electrode. In spite of some interesting comments about their perceived successes in the white paper I cited above, the grounding issue is usually overstated - the ground for lightning is the real issue, as any 10' 5/8" copper rod earth ground works for 60hz electrical safety. For safe termination of lightning downconductors and mast grounds etc, the best ground you can reasonably achieve is going to be enough - as long as the principles of bonding are adhered to religiously. That means as close to equipotential as possible, and it does not assume a good ground, or even any ground at all in certain cases. We surely want the best ground reasonably attainable, and if you can sink 30' of connected rods, great. If you sink a few 8-foot 5/8" or a couple of 1"x10', even better. See the data in that paper above for some sample resistance measurements which they consider "average" (ha - Richard Clark's laughing ;-), rightfully so. Best regards, Jack |
On Thu, 9 Sep 2004 23:45:44 -0400, "Jack Painter"
wrote: http://www.cpccorp.com/deep.htm See the data in that paper above for some sample resistance measurements which they consider "average" Hi Jack, Interesting link. The paper offered was a model of terse reporting, sticking only with the facts as best they could come by them, and little in the way of overextending themselves with fanciful interpretations. The averages were what they found for themselves, not abstracted and generalized to the world at large. I would suggest that they also made some cogent observations about the soil structure that goes beyond myths and software passing as the new age equivalent of old wive's tales. I would further observe that making a declaration of what the resistance of ONE electrode is, is farcical in the extreme. It would take two to tango and with that second one added to measure the first, problems abound! Especially notable is the 10 fold variation in reported electrode resistance over a 4 year period, and the 10 fold variation of electrode resistance within a survey group. Such an error range easily eclipses what is taken on faith as "average ground." And then we have to ask ourselves that embarrassing question, just how does the mud in my backyard compare to "average?" Your comments on That means as close to equipotential as possible, and it does not assume a good ground, or even any ground at all in certain cases. translate with fungible results to RF for the same reason. No one here knows what quality ground they live over (really! to one skin depth at HF?). I would still like to know how many radials Reggie needs for his several KOhm mud in his garden. No, I take that back, what I want to know is what parameters he puts into the software that predicts the number of radials - and why would it matter? 73's Richard Clark, KB7QHC |
"Richard Clark" wrote in message ... On Thu, 9 Sep 2004 23:45:44 -0400, "Jack Painter" wrote: http://www.cpccorp.com/deep.htm See the data in that paper above for some sample resistance measurements which they consider "average" Hi Jack, Interesting link. The paper offered was a model of terse reporting, sticking only with the facts as best they could come by them, and little in the way of overextending themselves with fanciful interpretations. The averages were what they found for themselves, not abstracted and generalized to the world at large. I would suggest that they also made some cogent observations about the soil structure that goes beyond myths and software passing as the new age equivalent of old wive's tales. I would further observe that making a declaration of what the resistance of ONE electrode is, is farcical in the extreme. It would take two to tango and with that second one added to measure the first, problems abound! Especially notable is the 10 fold variation in reported electrode resistance over a 4 year period, and the 10 fold variation of electrode resistance within a survey group. Such an error range easily eclipses what is taken on faith as "average ground." And then we have to ask ourselves that embarrassing question, just how does the mud in my backyard compare to "average?" Your comments on That means as close to equipotential as possible, and it does not assume a good ground, or even any ground at all in certain cases. translate with fungible results to RF for the same reason. No one here knows what quality ground they live over (really! to one skin depth at HF?). I would still like to know how many radials Reggie needs for his several KOhm mud in his garden. No, I take that back, what I want to know is what parameters he puts into the software that predicts the number of radials - and why would it matter? they 'why' is the real question as there are several reasons to design a 'ground' and each of them has different requirements. a few examples with different needs: 1. home electrical safety ground. 2. electrical substation ground. 3. hv transmission line ground for step or touch potential. 4. hv transmission line ground for lightning protection. 5. building ground for lightning protection. 6. building ground for rf isolation 7. vertical antenna ground for rf return these are all very different problems requiring very different solutions. i write software, part of which helps design grounds for hv transmission line structures. the theory and practice in this area is quite different from that used to design any of the other types (except maybe for small buildings requiring lightning protection). And some of the extensive testing we have done on the physics of the problem shows that the ground reacts quite differently from what most people expect when trying to dissipate lightning transients. i wouldn't use my software to design a ground for my station, though i did use some of the results of our tests to convince myself that what i did do would be adequate. Nor would i take any one other program as gospel when designing a ground for any particular type of installation. indeed at my station i have several different types of 'ground' systems, raised radials under elevated verticals, wire mesh mats on the ground under elevated verticals, ground rods at towers and service entrances, ufer grounds in foundations, perimeter ground around the house, each for a slightly different purpose and no one good enough for all the jobs that need to be done. Some help with rf radiation from antennas, some are lightning protection, and some are for ac safety. and they can't be interchanged in most cases... and some of them would not fit most layman's definition of what a 'ground' even is. |
On Thu, 9 Sep 2004 22:16:35 +0000 (UTC), "Reg Edwards"
wrote: |I am not very familiar with USA power-grounding regulations and they |probably vary from state to state. But I am under the impression that in |some simple circumstances, perhaps domestic, a single ground rod is |considered adequate for safety purposes. | |Under similar circumstances a maximum ground electrode resistance ( whatever |its construction ) of 50 ohms is specified. | |A 'standard' ground rod is 8 feet long and 1 inch in diameter. | |An average soil resistivity is 500 ohm-metres ( = 2 mS ). See Eznec? | |The calculated resistance of a single standard rod in average soil is 194 |ohms. ( I'm sure the calculating formula can be found somewhere on the IEEE |shelves. There ought to be greater use made of it. ) I responded to this in more detail but the post never came through. So more quickly this time see: http://www.usda.gov/rus/telecom/publ...s/1751f802.pdf [snip] |
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