------------------------------ Message: 26 Date: Tue, 20 Apr 2010 06:31:04 -0400 From: "Tom W8JI" <[email protected]> Subject: Re: [Elecraft] Grounding negative side of power supply? To: "Bob McGraw - K4TAX" <[email protected]>, "Jim Brown" <[email protected]>, "Elecraft List" <[email protected]> Message-ID: <321074f178104f4fab7715a73e6d1...@radioroom> Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original
<Refer to the NEC. It's their rule. As a side note, a loss of property covered by insurance may be dissallowed if they find improper grounding contributed to the damage. And they reference the NEC with regard to "proper".> I'm not so sure we aren't getting carried away with our own interpretation of NEC rules here. We also have to apply a little technical "common sense" to our systems. I have antennas and towers scatter over thousands of feet distance. It would be totally worthless and physically impossible to bond the ground rods on my antennas to my mains ground. The additional protection to my house and equipment, and to people, would be zero. In addition to no improvement in protection, the effectiveness of the low-noise antennas would be greatly decreased. Then we have to consider odds that power lines, trees, and our large towers would be ignored by lightning and a small ten-foot-tall twenty-foot-long, antenna would be struck. If it were struck, where would the majority charges move? In the feeder to the house. If the feeder ground were bonded to the mains ground at the building entrance, the safety issue for people and the dwelling is closed at that point. The ground at the dwelling entrance, that is mandated by NEC to be bonded to the mains ground, is key to safety. Not the critical signal ground at some backyard clothesline antenna. I also frequently hear that "insurance disallowed" statement. If insurance was "disallowed" for a NEC safety or rule violation, very few claims would ever be paid. In my entire life I can't recall having a claim denied because of something like this. I would bet well over half of Ham stations lack a proper entrance or station ground bonded to the mains ground, but I don't recall ever knowing of a claim disallowed for that gross error. 73 Tom =========================== Tom, and all: Have to agree with you. Hundreds of feet of electrical ground wire from antennas? Not even sure that would work for lightening. I have a ground rod at the base of my 600m inverted-L antenna (RF ground) and the 2-ft wide x 50-foot to 70-foot long radials are connected there. Z = 18 - j681.5 Rad = 0.8 ohms so most is ground loss I have a 120-foot run of 1-5/8 inch LDF7-50A Heliax that is grounded at the base of the tower and at the cable entrance to the shack. The cable entrance is a 12x 16 inch aluminum plate that has 26 coaxial feed thru connectors (I have over 17 antennas). The mains (electrical meter box) is grounded on the other side of the house so to bond them would take 50+28+50= 128 feet of ground wire. That might be effective if It was #6 or larger. I got better places to spend money. My Beverage antenna has two ground rods at either end but is 150-feet from the cable entrance. I have begun using ferrite RF Chokes a lot on my coax with excellent results. They are not expensive and nicer to look at then a big coil of coax. 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 144-600w, 432-100w, 1296-60w, 3400-fall 2010 DUBUS Magazine USA Rep [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
