Lighting/Surge protection
- Thread starter kurtmccaslin
- Start date
kurtmccaslin
Active Member
I have given the UFER ground some thought. Has anyone installed one of these recently?
I have some concerns about this. The typical foundation laid today has a 10 mil layer of poly tarp laid under it. Although this is probably not a barrier to lightning, I am concerned that it may reduce the effectiveness of a low voltage earth ground. Is it possible that Mr. Ufer did not have a plastic tarp under his foundation poured over 50 years ago-- and that gave it the concrete/ground contact that resulted in a good earth ground?
The 10 AWG wire is already in the ground (in the conduit between the structures). I ran 2 wire + ground in the conduit. It required 10 AWG because of the voltage drop over the 500 ft distance.
I have some concerns about this. The typical foundation laid today has a 10 mil layer of poly tarp laid under it. Although this is probably not a barrier to lightning, I am concerned that it may reduce the effectiveness of a low voltage earth ground. Is it possible that Mr. Ufer did not have a plastic tarp under his foundation poured over 50 years ago-- and that gave it the concrete/ground contact that resulted in a good earth ground?
The 10 AWG wire is already in the ground (in the conduit between the structures). I ran 2 wire + ground in the conduit. It required 10 AWG because of the voltage drop over the 500 ft distance.
kurtmccaslin
Active Member
It must be a regional thing. All the slabs I have seen in Texas have vapor barriers under them. This article says that old basement slabs did not have them and it caused cold, damp basements. http://www.concretenetwork.com/vapor-barriers/
It seems that this vapor barrier layer would reduce the electrical contact between the slab and the earth.
Unfortunately my ditch is already covered. I could have installed a bare wire in the ditch, but it is too late now. Is there any benefit to connecting the safety ground to a ground rod and surge protector at both ends of the 500 ft wire? At this point I am looking for something that gives me more protection than nothing (which is what I have now)
It seems that this vapor barrier layer would reduce the electrical contact between the slab and the earth.
Unfortunately my ditch is already covered. I could have installed a bare wire in the ditch, but it is too late now. Is there any benefit to connecting the safety ground to a ground rod and surge protector at both ends of the 500 ft wire? At this point I am looking for something that gives me more protection than nothing (which is what I have now)
rockinarmadillo said:
Apparently you are confusing a concrete floor with footings. In environments that have more rain, we still never used a vapor barrier underneath a concrete floor. We used crushed stone. And again, not under the footings (which must be on virigin earth for structural reasons).
Meanwhile, if the entire slab underneath an entire building is one big Ufer ground, then the entire building has superior equipotenial.
That safety ground wire exists between two structures. Any wire that enters a structure must be earthed where it enters that structure. It applies to all wires - even that safety ground wire. As demonstrated in this Tech Note:
http://www.erico.com/public/library/fep/technotes/tncr002.pdf
However safety code requirements also apply. That's what your electrician can best answer - to also satisfy the inspector..
Routing an earth ground wire between the single point ground for various structures is nice. But not critical and no where near as important as each structure having its own single point earth ground.
Neurorad
Senior Member
'Never use 2 ground rods, for the same structure, unless they are bonded.' - that's something that's been repeated many times, online. I believe it's a good rule. If a potential exists between the 2 ground rods, bad things happen.
So, magically, 2 structures, next to each other (not OP - his structures are widely spaced), can each have their own ground rod? If the structures are near to each other, should they be bonded? Or are they essentially bonded, given the large gauge conductors providing power and ground?
So, magically, 2 structures, next to each other (not OP - his structures are widely spaced), can each have their own ground rod? If the structures are near to each other, should they be bonded? Or are they essentially bonded, given the large gauge conductors providing power and ground?
Neurorad said:
This is why earthing is an art. A starting rule for transient protection says two structures within 20 feet can share a common earth ground. As long as all incoming wires first connect to that single point ground (directly or via a protector) before entering either structure.
Wire gauge is relevant to human safety and code requirements. Wire length is relevant to transistor safety and transient protection. Using a thicker wire does little to lower impedance. Whereas impedance is irrelevant to bonding for human safety, impedance is critically important for transistor safety. Another reason why earthing is an art.
Neurorad
Senior Member
Ah, 20 feet. Somewhat arbitrary, but that answers questions. Thanks. 20 feet of 8 AWG copper is cheap.
Wouldn't structures 100 feet apart suffer from a voltage potential, and be a setup for surge propagation, if each has a ground rod?
Be at one with voltage potentials - zen-like art. Understood.
Wouldn't structures 100 feet apart suffer from a voltage potential, and be a setup for surge propagation, if each has a ground rod?
Be at one with voltage potentials - zen-like art. Understood.
Neurorad said:
Connect a 200 watt transmitter to a long wire antenna. Touch one part of that antenna and feel no voltage. Touch another part to be shocked by maybe 100 volts. Why two completely different voltages on the same wire? To understand how electricity works means even understanding why two completely different voltages on the same wire.
Single point grounds for each structure means both structures can be at completely different voltages. But everything inside remains at near zero voltage. This relevant concept is called equipotential.
Surge protection addresses two concepts - equipotential and conductivity. Earthing is an attempt to do both since neither can be done sufficiently.
pete_c
Guru
A side tangent story....
Yup; here many years ago; 70's. Friend and I decided to put an antenna on his roof for radio communications between two homes.
There were grey clouds at a distance from the house; such that we were not worried about inclement weather.
We didn't see any lighting in the clouds at a distance.
We proceeded with the installation and wiring of the antenna to the inside of the house. The antenna port / box sat some maybe 12" away from the electrical outlet.
We decided to have a beer in the family room where we had wired up the antenna cable to taking a short break.
While sitting and chatting we heard a noise; like a zapping sound.
We looked over to where the antenna jack was and watched sparks going from the antenna jack to the electrical outlet.
It was more entertaining that watching television. This was the only time in my life that I have ever seen this happening.
Yup; here many years ago; 70's. Friend and I decided to put an antenna on his roof for radio communications between two homes.
There were grey clouds at a distance from the house; such that we were not worried about inclement weather.
We didn't see any lighting in the clouds at a distance.
We proceeded with the installation and wiring of the antenna to the inside of the house. The antenna port / box sat some maybe 12" away from the electrical outlet.
We decided to have a beer in the family room where we had wired up the antenna cable to taking a short break.
While sitting and chatting we heard a noise; like a zapping sound.
We looked over to where the antenna jack was and watched sparks going from the antenna jack to the electrical outlet.
It was more entertaining that watching television. This was the only time in my life that I have ever seen this happening.