26 ohms? We just completed a new 911 Centralized dispatch center here and the specs called for no more than 5 ohms from any point in the ground system to ground. I can tell you that there are 10 ft ground rods every 10 feet around the building and a 2/0 copper cable cad welded to every one of them. Several of them are in sandstone so they had to drill a larger hole and add enhancing material. Our building is over 7700 sq ft so you can bet there are a bunch of ground rods. The ground for the electrical service is also tied to this. In the dispatch area, there is a ground ring that goes around the room above the ceiling, the raised flooring is grounded to the ground system every 10 feet in every direction, all of the metal console cabinets are also attached to the ground. The metal water pipes entering the building are tied in also. To add to it, we also have a 320 ft tower at the site. There is a ground ring around the base of the tower, around our tower building and each of the 3 buildings for the wireless companies. There is a 2/0 cable to a static dissipation device at the top of the tower, and there is a ground ring around the top of the room in the tower building. Every coax has a ground kit at the antenna, at the base of the tower, and at the entry port. It then goes to a Polyphaser and then to the radio equipment. All of the racks and equipment are grounded to the ground ring also. The guy anchors are grounded back to the ground ring at the base of the tower. The ground ring at the tower and the one at the building are also tied together. I know this sounds like a lot, but in the last 4 years, the only problem I have had from a lightning strike was a tripped breaker on the circuit that powers the tower top preamp on our trunking system.
Jamey Wright Systems Admin Morgan County EMCD 911 Decatur, Al -----Original Message----- From: Mathew Quaife [mailto:[EMAIL PROTECTED] Sent: Tuesday, June 15, 2004 4:29 PM To: [email protected] Subject: Re: [Repeater-Builder] Re: grounds & cadwelding >>From what I remember from a Nipsco Rep, your ground should be 26 ohms throughout, but then and don't quote me on this, but seems to me that he mention to never connect to the ground for the electric company. Why that would be I could not say, but goes back to when I had a voltage problem here at home. Also different soils will change things, here where I am at, sand is all that is here, so we use salt pellets to enrich the ground. Mathew W9MWQ ----- Original Message ----- From: "Al Allum" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, June 15, 2004 11:37 AM Subject: Re: [Repeater-Builder] Re: grounds & cadwelding > Very true Laryn, however, he was not describing a single point ground, just > a ground system for the equipment in the shack, probably a better ground > then the house ground. Until he get a single point ground for EVERYTHING > I'll bet his new ground is better then the house ground so which was do you > think the current will flow? Try putting a volt meter between two different > grounds, you will probably get a reading. > > Al, N8ARO > > > > > ----- Original Message ----- > From: "Laryn Lohman" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Tuesday, June 15, 2004 9:32 AM > Subject: [Repeater-Builder] Re: grounds & cadwelding > > > > --- In [email protected], "Al Allum" <[EMAIL PROTECTED]> > > wrote: > > > John, > > > > > > Your idea sounds great for an RF ground system for your radios, > > however, it > > > will now leave you radios as a ground path from the house, power > > lines, > > > phone etc., to the great new ground > > > > > > > > But not if a *Single Point Ground* is used. That's the beauty of > > it... it keeps the equipment out of the path of lightning current on > > its way to ground. > > > > Laryn K8TVZ > > > > > > > > Yahoo! Groups Links > > > > > Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
