On Wednesday, January 4, 2017 at 8:24:20 PM UTC-5, James Wilkinson Swo=
Post by Dean HoffmanSome cut.
Post by James Wilkinson SwordI guess one doesn't test earth grounding with a regular oh=
m meter.
Post by Dean HoffmanPost by James Wilkinson SwordYou guess?
The instructor at one of my code refresher classes asked once =
if
Post by Dean HoffmanPost by James Wilkinson Swordanyone had
the correct type of tester. No one did out of at least 50
electricians. Earth grounding
is primarily for damage from lightning. He also had a diagram sh=
owing
Post by Dean HoffmanPost by James Wilkinson Swordhow little current would flow through the earth if a well motor h=
ad a
Post by Dean HoffmanPost by James Wilkinson Swordshort to the frame. The resistance was so high that there was no=
way
Post by Dean HoffmanPost by James Wilkinson Swordeven a tiny fuse would blow if there was a short.
<http://support.fluke.com/find-sales/Download/Asset/2633834_6115_=
ENG_A_W.PDF>
Post by Dean HoffmanPost by James Wilkinson Sword"A good grounding resistance is 5 ohms or less" - well since I got=
20
Post by Dean HoffmanPost by James Wilkinson SwordMOhms, I guess that isn't grounded.
So did you use an actual ground tester or a volt/ohm meter=
? It
Post by Dean Hoffmansure seems odd that
your results don't match Mr. Ufer's and bunches of people after him=
.
Post by Dean HoffmanAn article in Electrical Contractor magazine says Ufer's groundi=
ng
Post by Dean Hoffmanelectrodes kept the resistance at 2-5 ohms over a 20 year period.
<> http://www.ecmag.com/section/codes-standards/what-ufer-ground>
Resistance is resistance. Concrete does NOT conduct. WATER conducts=
. Concrete is a porous material which may or may not contain water. Th=
e floor of your house should never contain water, or you have BIG proble=
ms, way above a possibility of shock.
--
"VAT is a simple tax..." -- Anthony Barber, Chancellor of the Exchequ=
er on the introduction of VAT on April Fool's Day in 1973.
http://www.esgroundingsolutions.com/different-types-of-grounding-elect=
rodes/
Ufer Ground or Concrete Encased Electrodes
Originally, Ufer grounds were copper electrodes encased in the concret=
e surrounding ammunition bunkers. In today=E2=80=99s terminology, Ufer g=
rounds consist of any concrete-encased electrode, such as the rebar in a=
building foundation, when used for grounding, or a wire or wire mesh in=
concrete.
Concrete Encased Electrode
The National Electric Code requires that Concrete Encased Electrodes u=
se a minimum No. 4 AWG copper wire at least 20 feet in length and encase=
d in at least 2 inches of concrete. The advantages of concrete encased e=
lectrodes are that they dramatically increase the surface area and degre=
e of contact with the surrounding soil. However, the zone of influence i=
s not increased, therefore the resistance to ground is typically only sl=
ightly lower than the wire would be without the concrete.
Concrete encased electrodes also have some significant disadvantages. =
When an electrical fault occurs, the electric current must flow through =
the concrete into the earth. Concrete, by nature retains a lot of water,=
which rises in temperature as the electricity flows through the concret=
e. If the extent of the electrode is not sufficiently great for the tota=
l current flowing, the boiling point of the water may be reached, result=
ing in an explosive conversion of water into steam. Many concrete encase=
d electrodes have been destroyed after receiving relatively small electr=
ical faults. Once the concrete cracks apart and falls away from the cond=
uctor, the concrete pieces act as a shield preventing the copper wire fr=
om contacting the surrounding soil, resulting in a dramatic increase in =
the resistance-to-ground of the electrode.
Ufer Ground or Building Foundations
Ufer Grounds or building foundations may be used provided that the con=
crete is in direct contact with the earth (no plastic moisture barriers)=
, that rebar is at least 0.500 inches in diameter and that there is a di=
rect metallic connection from the service ground to the rebar buried ins=
ide the concrete.
If you bothered to look at your own country's codes, you'd see
that Ufers are one of the allowed types of grounding in the UK.
https://books.google.com/books?id=3D-120XiXXOCoC&pg=3DSL3-PA133&lpg=3D=
SL3-PA133&dq=3Dearthing+electrode++542-02-01&source=3Dbl&ots=3DkD-d0hdo4=
A&sig=3DcF6fUcCSksgbN1uRBTtI6EabUqA&hl=3Den&sa=3DX&ved=3D0ahUKEwik_7vlm6=
vRAhXs7IMKHSMDCqkQ6AEILjAE#v=3Donepage&q=3Dearthing%20electrode%20%20542=
-02-01&f=3Dfalse
"Handbook of the Wiring Regulations" (UK)
Based on BS 7671 2001 edition
It's page C2/15, they show 7 types of allowed earth grounds,
two of the 7 are metal electrodes embedded in concrete.
But then you say codes don't matter and you've demonstrated
that you're one of the village idiot trolls, so I'm sure
that won't change anything either.
20 feet deep. How deep is the concrete in your floor? 6 inches?
-- =
I know you believe you understand what you think I said,
but I'm not sure you realize that what you heard is not
what I meant.