[TowerTalk] TowerTalk Digest, Vol 43, Issue 14
daweezil2003 at yahoo.com
Wed Jul 5 13:19:10 EDT 2006
Re: 20 ft. Ufer CEGE
The 20 ft. length has seemed to hang up many on its ability to do everything needed for lightning protection. That was not the intention of the original post. The 20 ft. is the MINIMUM required by the NEC. In the case of JC for whom I was discussing he would have 34 ft. assuming 3 in. spacing in from the edge of pour and not counting the leads to connect it to the surface of the slab.
He was also considering additional copper around outside of base in the bentonite which is still in the area of dissipation of the Ufer and there for not a lot more useful but in no way harmful unless he disturbed soil that the base load calculations depended on. Additional grounding would better be accomplished by ground rods at LEAST the 8 ft. NEC calls for in a pattern that was at least the length of rod spaced from each other and the base all bonded to the common point (now a buss with multiple connections) ground connection.At rocky sites I have had to have a rock drilling company come in and drill holes up to 50 ft. deep and put in screw together ground rods with a enhancing additive surrounding them. Also everything on commercial grids are "Cadwelded" instead of bolted.(This is not the average do-it your self home project)
Also the #2 cu is a minimum with #2/0 or #4/0 being the norm on grids.
A Ufer in no way is a substitute for a ground radial system needed by a vertical antenna structure. The number, layout, and type of wires for that is another whole thread.
The ability of lightning to strike in other than the top of the tower is well documented and addressed by the various companies the make dissipation devices. Most all recommend devices at no more than 50 ft. intervals and some even recommend them on insulated guy wires. They cite Field gradient differences along sections that create arcing across insulators without strikes degrading insulator quality.
How low will we go? Check out Yahoo! Messengers low PC-to-Phone call rates.
More information about the TowerTalk