Ufer Grounding

[mike90045]

USA East Coasters may not know about this method, but it is widely used in California. Here's a couple of links to data about it.

""The principle of the Ufer ground is simple, it is very effective and inexpensive to install during new construction. The Ufer ground takes advantage of concrete’s properties to good advantage. Concrete absorbs moisture quickly and looses moisture very slowly. The mineral properties of concrete (lime and others) and their inherent pH means concrete has a supply of ions to conduct current. The soil around concrete becomes "doped" by the concrete, as a result, the pH of the soil rises and reduces what would normally be 1000 ohm meter soil conditions (hard to get a good ground). The moisture present, (concrete gives up moisture very slowly), in combination with the "doped" soil, make a good conductor for electrical energy or lightning currents.""


http://www.psihq.com/iread/ufergrnd.htm
http://www.scott-inc.com/html/ufer.htm



text attachments (as links on the web fail often)

[niel]

that may work good for really bad soil and you must have a very large area of concrete with the reinforcing bars. this is not your 3' deep and 3' around type of arrangement for a small pole as we're talking in 10s of feet around and of course much deeper. if it were as simple as just using the rebar for a ground then many amateur radio operators would have the green light to use their towers rebar cage as the ground. this is not the case as i know of not 1 that this would suffice for normally and a ground rod is needed for each leg of a tower and is usually cojoined to the rebar cage too. as they stated, it is good only when the soil resistance is higher than the concrete's that this is ok to do and the concrete must cover a wide area of ground. imho the concrete will eat away some of the wire as concrete is acidic so even larger wires should be used over the normally larger wires that would've been used in soil.
when it comes to the nec and the inspectors you better be prepared to prove the soil is worse than the concrete in resistance. you also must show that the concrete is to be sufficient to take the place of a good large area ground screen and that it will not be eaten away prematurely by the concrete. even at that they may require periodic inspections to verify it to still be good.

[JESSICA]

Niel:

Can you explain why the grounding rod has to be inserted about 8 to 10 feet in the ground?

If the purpose of the grounding rod is just to transmit electricity to the soil, why are 3 or 4 feet just not good enough?

[niel]

in many areas it has been determined that even 8ft isn't enough, but the nec had to make a determination for a standard somewhere. where someone is on rock this is obviously a problem, but it is not impossible to work around. an 8ft copper ground rod has a given amount of area of contact with the soil and it points in a direction into the earth to divert away from other possible problems, like those of us with basements or cellars. ground screens are an alternative and the concrete example in this thread is a form of a ground screen and they are not small because they must have a great deal of contact area with the earth and areas with rock tend to not hold much moisture so even larger areas of contact could be in order over that which would have been acceptable to those in soiled areas (maybe i should've said earthened areas?). soil holds moisture well and thusly holds good electrical conductivity too. local inspectors may need to be consulted for what will be acceptable in such rocky environments if any inspectors are there. if there aren't any inspectors then a good electrician can be consulted and mind you not all are experts on grounding as would be evidenced by any insisting you drill into the rock for an 8ft ground rod. note that some less than knowledgeable inspectors may also insist upon drilling for a ground rod too.

[icarus]

I'm no expert on NEC, but I have this memory that grounding systems (at least in residential service) could meet a particular resistance to ground to qualify as proper grounding. I know that one jurisdiction I used to work in required 2 rods, sharing a common wire within 10' of one another. The rational was that one rod couldn't meet the resistance requirement. I have no idea of what that requirement is.

What I have done on my Canadian Shield island, mostly bedrock with a thin layer of duff, is find a small section of sand and clay, dug a pit (since driving anything is impossible given the glacial boulders everywhere!) buried a rod diagonally in the pit to maximize surface area. I also wound the copper wire around the zinc rod over it's length to maximize contact. The bare wire lays on the ground for ~ 100' so the total surface area is fairly good.

My major concern is lightning protection. I have a 30' mast with an vertical antenna on it. I have bonded the mast, the steel chimney, as well as the roof mounted panel frames to the above ground wire. This also joins the ground wire from the 120vac panel. Question is, if lightning hits the antenna, will I energize the house as a result?

Tony

[niel]

"Question is, if lightning hits the antenna, will I energize the house as a result?"

odds are some of that energy will enter the house no matter what, but you hope that enough is diverted to prevent damage or shock. if that is for a 2way radio then some sort of discharging arrangement at the coax just before it enters the house and down to your ground system would be in order. http://www.ba-electronics.com/a28.htm that one would be an air gap and there are gas types out there too that discharge it faster, but are blown after the first discharge making things vulnerable to secondary strikes and emp. disconnecting the coax helps minimize some damage possible to the radio itself, but may still jump to it during a strong emp or direct strike.
similar things can be done for tv and satellite stuff too.

[machineman]

I have one of those Ufer grounds installed in my mobile home concrete 6" wide stem wall foundation. The wall is 24" above grade and the pertruding ground wire is 4gauge which connects the steel undercarraige of the home. The steel undercarraige is also grounded to the main panel. Passed building inspection. I also installed a ground rod near my back-up generator which also ties into the main panel via 40' of 2-3 wire with #8 ground. I'm off grid so and no solar panels yet till I save up some more $$$.