Bonding the UFER

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mbrooke

mbrooke

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Is this a good example of why its important to bond the UFER to the service? In essence bonding the UFER (and all other exposed conductive parts) creates an equal potential like mesh or cage that protects the occupants should the system become elevated in voltage relative to remote earth (such as an open neutral). Its not the contact with soil which makes a UFER so important, but rather eliminating another point which may present a difference of potential. Its not grounding, its bonding, correct?


Here are three videos that may demonstrate my theory where crews work a transmission line live. The crews wear a conductive suit and are within a metal lined bucket that bonds to the transmission line to help protect them, something which goes against what most would assume.


https://www.youtube.com/watch?v=R9QJGXln1lE


https://www.youtube.com/watch?v=IYXgMbgASJ4

https://www.youtube.com/watch?v=6MXMJ_7mGxQ


So is what really protects people bonding rather then grounding?
 
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GoldDigger

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The CEE does provide a low impedance path to earth for the fault current, and might even be low enough to trip a 20 breaker on a 120V circuit (i.e. less than 6 ohms.)
But it is there primarily to provide a path for lightning induced current and to provide an earth reference for the POCO secondary if the pole ground gets interrupted.
It is true that it also provides an equipotential surface for people in bare feet, but that is not the reason it is in the code and is preferred to ground rods.
The code does not call it a CEE or require bonding if the bottom of the concrete is insulated from the dirt.
As for the linemen, errr line persons, the problem is capacitive current at that voltage. You are better off being inside the capacitor rather than being the conductor leading to one plate of the capacitor.
 
mbrooke

mbrooke

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GoldDigger said:
The CEE does provide a low impedance path to earth for the fault current, and might even be low enough to trip a 20 breaker on a 120V circuit (i.e. less than 6 ohms.)
But it is there primarily to provide a path for lightning induced current and to provide an earth reference for the POCO secondary if the pole ground gets interrupted.
It is true that it also provides an equipotential surface for people in bare feet, but that is not the reason it is in the code and is preferred to ground rods.
The code does not call it a CEE or require bonding if the bottom of the concrete is insulated from the dirt.
As for the linemen, errr line persons, the problem is capacitive current at that voltage. You are better off being inside the capacitor rather than being the conductor leading to one plate of the capacitor.
Click to expand...


Correct, but is a perfectly insulated UFER possible?
 
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GoldDigger

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mbrooke said:
Correct, but is a perfectly insulated UFER possible?
Click to expand...
If it is perfectly insulated it is not a UFER.
Mr. Ufer's whole purpose was to get a useful earth connection on dry rocky soil.
Radio transmitters at low frequency need a good connection to the actual earth, as does a lot of other RF electronics exposed to nearby lightning.
 
mbrooke

mbrooke

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GoldDigger said:
If it is perfectly insulated it is not a UFER.
Mr. Ufer's whole purpose was to get a useful earth connection on dry rocky soil.
Radio transmitters at low frequency need a good connection to the actual earth, as does a lot of other RF electronics exposed to nearby lightning.
Click to expand...



Correct, but my theory is that it should still be bonded since it would be almost impossible to isolate it from earth, and even then capacitive coupling plays a role.

While a true UFER provides exceptional earthing, my theory is that it plays an even bigger role: providing some (a good) level of equal potential to the occupants within a building.
 
iwire

iwire

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mbrooke said:
Correct, but my theory is that it should still be bonded since it would be almost impossible to isolate it from earth, and even then capacitive coupling plays a role.

While a true UFER provides exceptional earthing, my theory is that it plays an even bigger role: providing some (a good) level of equal potential to the occupants within a building.
Click to expand...

It strikes me that you may not understand what an NEC concrete encased electrode is and where it is installed.

From 2011 NEC 250.52(A)(3).

Metallic components shall be encased by at least
50 mm (2 in.) of concrete and shall be located horizontally
within that portion of a concrete foundation
or footing that is in direct contact with the earth or
within vertical foundations or structural components
or members that are in direct contact with the earth.
Click to expand...

It is installed in the footing not the slab and the slab is most times isolated from the foundation and footing

Check this out

stemwallslab.gif


In this application the CEE would be in the footing 2' to 4' underground and away from human contact. Notice the slab is isolated from the foundation.
 
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