robt65
Feb 24, 2011, 8:31 AM
Post #26 of 31
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Re: [turnabout] Building Natural Stone Posts for Electric Lamps and Metal Gates
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The NEC Code requires you to space rods at least 6 feet apart [250.53(B)]. This spacing is a minimum — and far from ideal. When using the typical 8-foot or 10-foot ground rod, you get the best results by spacing the rods at least 16 or 20 feet apart, respectively. This is much greater than the Code minimum 6-foot spacing. If the rods are longer they should be further apart. "If you are very concerned about soil resistively you could always install 3 or 4 rods".
Ground rods spaced less than two rod-lengths apart will interfere with each other because their effective resistance areas will overlap. For reference, see IEEE-142 and Soares Book on Grounding. The overlap increases the net resistance of each rod, making the grounding electrode system less effective than if the rods were spaced farther apart.
Grounding rods must be at least 8ft long, 5/8" in diameter, a resistance that does not exceed 25 ohms (NEC 250.56), typically located 2ft away from the house, and driven vertically into the ground. But, if you can't manage to get it vertically down into the ground, while it is permitted to lay a grounding rod horizontally in a trench in the ground at least 2 1/2 ft deep or to drive it in at a 45 degree angle, just as long as there is at least 8ft of length in contact with the soil, I do have what appears to be a different soil depth (but very dry) and a water table could be reached at a depth of 14 to 17 feet, making a good conductivity.
Note that if the resistance is over 25 ohms or there is very dry soil (damp soil will help to lower ground resistance and dissipate the energy better), you may want to put a second grounding rod in. Place it a minimum of 6ft away from the first. It can also be laid horizontally and must be connected with a jumper cable. No less than 6'. There are rods made that have the ends threaded to add length.
I plan on using my grounding system also for a lightning protection system, which I may want to consider for peace of mind, since we do get a lot of electrical storms.
There are also 3/4" x 10' ground rods that are available at some electrical supply companies, but my depth of water table is greater than 10 foot. I do have a shelf that I believe one ten foot rod (21 feet apart) from two 8 foot rods threaded together would reach. I know this will be over the heads of some, but my information comes from the NEC which I certainly trust over some posters idiotic remarks on this forum.
robt65
A distance of 16' or more from each other is optimal for 8' rods. If the rods are longer they should be further apart. Since I am concerned about soil resistively, I will be installing 3 or possibly 4 rods, (threaded two together) given the depth of the local ground water.
Ignorance is bliss isn’t it turnaround or is it turnabout? But maybe you just can’t understand what the cost of replacing an entire household of major electrical appliances (stove, microwave, side by side refrigerator, 3 flat screen televisions, air conditioners or mini splits, telephone system and several computer systems) would cost, not to mention the loss of spoiled foods. Better skip and whistle back to your tent in SMA and reflect on your ignorance.
(This post was edited by robt65 on Feb 24, 2011, 9:01 AM)
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