Here is an article that described a Ufer ground failure that prompted the installation of an extensive external grounding system on a 1900’ BC tower.
http://www.radioworld.com/headlines/0045/proper-grounding-and-bonding-are-crucial/338510 The Broadcast industry doesn’t seem to put their faith in Uber grounding. Rick > On Apr 18, 2017, at 12:25 AM, David Gilbert <[email protected]> wrote: > > > You also have many thousands of ham radio towers in northwest 7 land with > either Ufer grounds or embedded tower bases. You tell me how many of them > have exploded during lightning strikes, and how that justifies the admonition > to "never encase a ground rod in a tower base". > > I once did an extensive internet search trying to find documented examples of > concrete structures that had exploded from the inside out due to internal > grounded conductors. I couldn't find a single one. Maybe you can find one, > and if so I'd like to see the link. I did find several instances of damage > to concrete structures from lightning hits, but all of them had external > damage from simple lightning strikes. Most other damage was attributed to > the fact that there wasn't any grounding at all ... i.e., an ungrounded > structure on top of a concrete base. > > From a theoretical point of view, I could picture a discharge causing more > damage from insufficient metal in the concrete rather than too much. Spread > the current ... minimize the heat buildup. If you want to argue that a single > ground rod in a concrete base is a poor idea, OK ... I can buy that. But > these other blanket statements are garbage science. > > Dave AB7E > > > > On 4/17/2017 10:45 PM, Rick Dettinger wrote: >> A Uber ground was developed for dry areas during WW2. In damp areas, the >> concrete can do just what happened in the concrete pole test. >> >> Per Wikipedia article: >> "A disadvantage of Ufer grounds is that the moisture in the concrete can >> flash into steam during a lightning strike or similar high energy fault >> condition. This can crack the surrounding concrete and damage the building >> foundation.” >> >> We have plenty of damp soil in northwest 7 land. >> >> Best, >> Rick >> >>> On Apr 17, 2017, at 9:57 PM, David Gilbert <[email protected]> wrote: >>> >>> >>> That isn't even close to being the same condition and only serves to help >>> perpetuate a stupid myth that refuses to die among the ill informed. >>> Anyone that doesn't understand that a Ufer ground is essentially multiple >>> ground rods encased in concrete is indeed ill informed. And anyone who >>> doesn't understand the mechanisms and considerations behind a Ufer ground >>> shouldn't be making contributions to threads like this. >>> >>> Sorry for the ire displayed by me here, but this stupid topic keeps >>> surfacing year after year in ham radio circles ... and specifically this >>> forum ... without the least bit of thoughtful consideration behind it. I'm >>> tired of our hobby, supposedly a technically based one, being subject to >>> definitively stated exhortations that are so demonstrably wrong. >>> >>> Dave AB7E >>> >>> >>> >>> On 4/17/2017 9:09 PM, Rick Dettinger wrote: >>>> I don’t think its a myth. In the early 1970’s, the power company I worked >>>> for was testing out some hollow reinforced concrete poles. There was >>>> considerable concern by the line workers that the poles might be more >>>> dangerous to work on than wooden poles, in the event of an accident. To >>>> check this, we installed one of the poles in a sub station, and wrapped a >>>> 26KV 1200 amp feeder conductor around the pole. When the station breaker >>>> was closed, the pole exploded dramatically, with a large fireball. The >>>> results might have something to do with moisture content in the concrete. >>>> The results convinced us to only use the poles on transmission lines that >>>> wouldn’t be worked hot, like we did with distribution lines. Of course, >>>> the power levels are much higher in lightening strikes. The conduction >>>> paths should similar from encapsulated ground rods in a tower base to >>>> Earth. >>>> >>>> 73, >>>> Rick K7MW >>>> >>>> >>>> >>>>> On Apr 17, 2017, at 8:32 PM, Doug Renwick <[email protected]> wrote: >>>>> >>>>> That myth refuses to die. I have 5 concrete tower bases with ground rods >>>>> partially encased and never a worry about an exploding base. >>>>> >>>>> Doug >>>>> >>>>> >>>>> -----Original Message----- >>>>> >>>>> -NEVER- encase a ground rod in concrete ... especially a tower base. >>>>> >>>>> As a retired 2-way radio tech, I'm aware of two towers that had to be >>>>> re-installed because of lightening strikes exploding their concrete bases. >>>>> >>>>> 73! >>>>> >>>>> Ken - K0PP >>>>> >>>>> >>>>> >>>>> --- >>>>> This email has been checked for viruses by Avast antivirus software. >>>>> https://www.avast.com/antivirus >>>>> >>>>> ______________________________________________________________ >>>>> Elecraft mailing list >>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>>> Help: http://mailman.qth.net/mmfaq.htm >>>>> Post: mailto:[email protected] >>>>> >>>>> This list hosted by: http://www.qsl.net >>>>> Please help support this email list: http://www.qsl.net/donate.html >>>>> Message delivered to [email protected] >>>> ______________________________________________________________ >>>> Elecraft mailing list >>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>> Help: http://mailman.qth.net/mmfaq.htm >>>> Post: mailto:[email protected] >>>> >>>> This list hosted by: http://www.qsl.net >>>> Please help support this email list: http://www.qsl.net/donate.html >>>> Message delivered to [email protected] >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:[email protected] >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >>> Message delivered to [email protected] >> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
