Is a UFER or CEE required to have a resistence of 25 ohms or less?

[Sierrasparky]

HI have a question on UFER.
Is a UFER / CEE required to be proofed to show 25 ohms or less?
I am aware of the requirements of a plate or rod electrode.

Thanks

 

[LarryFine]

Negative. No minimum measurement, and no rods required.

 

[ActionDave]

Negative. No minimum measurement, and no rods required.

I don't understand. Could you be more clear?

 

[LarryFine]

I don't understand. Could you be more clear?

There is no minimum resistance measurement requirement, and there is no requirement for additional made electrodes.

 

[ActionDave]

There is no minimum resistance measurement requirement, and there is no requirement for additional made electrodes.

You are correct. I was making a joke. I understand how that could be missed since I rarely use smileys.

 

[LarryFine]

I was making a joke.

I was wondering what I missed.

 

[Sierrasparky]

Thanks Larry! .
It never ceases to amaze me what a EE will say. "


Either a 20 ft length of copper cable can be installed in the slab or a shorter length of copper cable can be bonded to the rebar which totals at least 20 feet in length. Again, it is all about achieving the maximum 25 ohms ground resistance. "

 

[LarryFine]

Again, it is all about achieving the maximum 25 ohms ground resistance. "

Don't take that to be a requirement; it isn't. And, 25 ohms IS futile.

 

[GoldDigger]

Thanks Larry! .
It never ceases to amaze me what a EE will say. "


Either a 20 ft length of copper cable can be installed in the slab or a shorter length of copper cable can be bonded to the rebar which totals at least 20 feet in length. Again, it is all about achieving the maximum 25 ohms ground resistance. "

That is indeed monumentally stupid!
In addition to the second sentence, it does not recognize the requirement for a footer rather than just a slab and the exclusion if it does not have direct earth or other substrate contact. Not to mention rebar diameter and lack of coating.

 

[drcampbell]

I think the original concept might be that a Ufer ground doesn't require good conductivity with the Earth because the slab becomes an equipotential "earth"-reference point, much like the hull of a ship in fresh water.

Of course, coated rebar and corrosion of uncoated rebar do make me wonder about its performance.

 

[GoldDigger]

I think the original concept might be that a Ufer ground doesn't require good conductivity with the Earth because the slab becomes an equipotential earth-reference point, much like the hull of a ship in fresh water.

Of course, coated rebar and corrosion over its lifetime remain problematic.

The entire evolution of the Ufer ground, by Ufer, was to deal with high resistance desert soil.
The key is in the enormous surface area compared to other made grounds, just as with the ship's hull.

 

[tom baker]

The entire evolution of the Ufer ground, by Ufer, was to deal with high resitance desert soil.
The key is in the enormous surface area compared to other made grounds, just as with the ship's hull.

That is a very good analogy and if I was still teaching I would use it.

 

[Sierrasparky]

The entire evolution of the Ufer ground, by Ufer, was to deal with high resitance desert soil.
The key is in the enormous surface area compared to other made grounds, just as with the ship's hull.

Agreed, I do not know how those words came from a EE. I do wonder where EE's come up with more stringent grounds like for Cell towers?

 

[tom baker]

Because the design of cell tower grounding allows them to withstand most direct lightning hits. The designs are based on physics.

 

[electrofelon]

Because the design of cell tower grounding allows them to withstand most direct lightning hits. The designs are based on physics.

I don't know Tom.....maybe partly, but I have seen (and had to install) GES at cell towers and needed to meet a spec of 5 ohms. I'm pretty sure that figure was pulled out of someone's posterior area...... besides my understanding is lightning doesn't "care" much about DC resistance.

 

[tom baker]

One of our mods, DC Campbell has a lot of experience with cell towers, I will ask him to comment