Concrete encased electrode. Ufer Rod

[Max]

lightning protection is provided by a separate installation if you want it added
i have seen lightning use a #6 ground wire as easily as it did the 12AWG in the house wiring

Sure. For a direct hit you’re talking tens of thousands of amps.

 

[Max]

as i mentioned elsewhere
the nec is not always the final word on what is acceptable
however the AHJ is the final word and we have to trust him to be knowledgeable of what his jurisdiction has adopted
this may include all or part of the code, in addition to local, city, county, state codes that may be adopted and allowed to add to
or omit parts of the code. As well as utility requirements who can add to whatever they choose, but not omit

when i said two rods i was replying to someone who said two rods and agreeing with them

my state is louisiana and they have a state building code in addition to the nec
they require two rods, or a ufer and one rod, but always 2 points of grounding

I am actually much more familiar with electrical principles than I am with the NEC. I can hum a few bars of the NEC, but there are people here that are truly experts - and I am not one of them.

My original issue with your comment about stabilization is that the ground does nothing to stabilize the incoming voltage. Now that you are talking about a floating neutral I understand better about what you were trying to say.

However I still think that even in your example you are wrong. Think about the house ground‘s relationship to wherever the closest power co ground is. It could be 10 feet, 100 feet, or 1000 feet. The earth can and will have a significant resistance between those points (10s of thousands to millions of ohms), so any appreciable current through that path will drop a lot of voltage - making any stabilization effect useless.

When you lose a neutral the voltage you see on each leg is a function of the impedance of each leg. Say all you have turned on for one leg is a 10A heater. Similarly the other leg has only a 10A heater. Disconnect the ground as a test and you will still se 120V on each leg. But now add a third heater onto either leg and you will see an imbalance.

BTW, I am not trying to “win” anything here - just noting an error so that people that read this thread later are not confused. I am not upset with you and I hope you are not upset either. Lord knows that I have made plenty of errors myself…

 

[Half-fast eddie]

0) Provides a path to earth for things like lightning.

Sometimes with unintended consequences …

“A disadvantage of Ufer grounds is that the moisture in the concrete can flash into steam during a lightning strike or similar high energy fault condition. This can crack the surrounding concrete and damage the building foundation.”

 

[sparky 1971]

I haven't read all of the posts, but I have seen quite a few wrong statements. A UFER is supposed to be connected to the rebar in the footing or to rebar that is attached to rebar in the footing, not a floating slab. When a UFER is used, ground rods are not required, but bonding to any metal piping that is in contact with earth for more than 10 feet still is.

I can only think of two places I've wired where the UFER was installed, everywhere that one wasn't installed, two ground rods took care of it, so if a UFER isn't there, it's not the end of the world.

Ufer ground | Electrical Code Requirements – CONSTRUCTION INSPECTION TIPS

constructioninspectiontips.com

 

[u2slow]

A single plate electrode 2' deep works too.

Don't know why the NEC hasn't adopted it's use.

 

[Almost Retired]

I am actually much more familiar with electrical principles than I am with the NEC. I can hum a few bars of the NEC, but there are people here that are truly experts - and I am not one of them.

My original issue with your comment about stabilization is that the ground does nothing to stabilize the incoming voltage. Now that you are talking about a floating neutral I understand better about what you were trying to say.

However I still think that even in your example you are wrong. Think about the house ground‘s relationship to wherever the closest power co ground is. It could be 10 feet, 100 feet, or 1000 feet. The earth can and will have a significant resistance between those points (10s of thousands to millions of ohms), so any appreciable current through that path will drop a lot of voltage - making any stabilization effect useless.

When you lose a neutral the voltage you see on each leg is a function of the impedance of each leg. Say all you have turned on for one leg is a 10A heater. Similarly the other leg has only a 10A heater. Disconnect the ground as a test and you will still se 120V on each leg. But now add a third heater onto either leg and you will see an imbalance.

BTW, I am not trying to “win” anything here - just noting an error so that people that read this thread later are not confused. I am not upset with you and I hope you are not upset either. Lord knows that I have made plenty of errors myself…

i am not upset either, and will not get that way
but you are also mistaken about how current travels through the earth
ohms law
electricity takes all available parallel paths
the current will spread out in the earth and not actually encounter that much resistance or voltage drop

having said that ,
i can assure you that if you lose all connections to earth and utility neutral
you will have 240V on one leg and 0V on the other
this is primarily due to how the transformer on the pole is built and connected

i have measured 240V and 0V to earth with a good voltmeter on an existing house

this occurred because a log truck that was loaded too high snagged and broke the utility neutral, but not the hot legs
(dont ask me how they got that unlucky)

 

[wyliesdiesels]

The trick to the concern of the rebar not being electrically continuous is that concrete is extremely conductive
this is the reason that GFCI protection is required in garages and unfinished basements

if the concrete is not allowed to touch the earth, then it is not grounded to the earth
however the ufer connection connects it to the panel grounding system which must also be connected to an external grounding system such as two ground rods a minimum of 6' apart but no specified distance from the slab

there are two reasons to connect all electrical systems to earth ground
1) it prevents a shock occuring because of voltage difference between the earth and say the meter can, (but not the interior if it is live)
2) it also stabilizes the voltage supplied by the utility

How so? That doesnt make sense... there is no reference between the ground rod at the house and the substation transformer.

Perhaps you meant it stabilizes voltage potential to earth since it puts earth at the same potential... in other words, so that someone cant get shocked when they touch the panel enclosure

 

[wyliesdiesels]

A single plate electrode 2' deep works too.

Don't know why the NEC hasn't adopted it's use.

We could use plate electrodes here but rods or UFERs are easier..

 

[wyliesdiesels]

i am not upset either, and will not get that way
but you are also mistaken about how current travels through the earth
ohms law
electricity takes all available parallel paths
the current will spread out in the earth and not actually encounter that much resistance or voltage drop

having said that ,
i can assure you that if you lose all connections to earth and utility neutral
you will have 240V on one leg and 0V on the other
this is primarily due to how the transformer on the pole is built and connected

i have measured 240V and 0V to earth with a good voltmeter on an existing house

this occurred because a log truck that was loaded too high snagged and broke the utility neutral, but not the hot legs
(dont ask me how they got that unlucky)

That anecdotal story has nothing to do with your previous statement. It has to do with MWBCs and lost neutral.

Also, the earth is a poor conductor of electricity and electricity returns to its source (transformer) not the earth. No the current wont spread out through the earth and because its a poor conductor, there wont be much of any current flowing through the earth and back to the center tap on the transformer via the pole ground rod...

If the earth was low resistance, and all the neutral current could return back to the transformer via the ground rod, then you wouldnt have had the unbalanced voltage due to lost neutral.... you actually contradicted yourself here

 

[u2slow]

We could use plate electrodes here but rods or UFERs are easier..

Funny.... plates are mostly used here because it's cheaper/easier.

 

[billconner]

So many types of electrodes.

Types of Electrodes

The National Electric Code (NEC) requires that driven rods be a minimum of 8 feet in length and that 8 feet of length must be in direct contact with the soil. Typically, a shovel is used to dig down into the ground 18 inches before a driven rod is installed.

esgrounding.com

 

[Half-fast eddie]

So many types of electrodes.

Did someone say electrodes?

 

[TRWham]

I think i’m right with the following statements. If not, i hope someone will correct me. (Hah! As if anyone here would hold back.)

1. The term Ufer is not in the NEC.
2. What everyone calls an ufer ground is actually just bonding to the rebar in the foundation.
3. A code compliant ground rod is still required, in addition to the rebar bond.

The term Ufer may not be, but a very good, even perfect, description of one is in 250.52(A)(3). The requirement for a supplemental ground electrode (250.53(A)(2)) applies to rod, pipe and plate electrodes. Code references are to the 2020 version.

 

[TRWham]

i will respectfully differ
until something goes wrong you are correct, it does not help,
but if you lose your utility neutral connection, as well as your ground connection for your house
you will instantly have 240V on one leg, and 0V on the other (that is how the pole transformer is built)
i have seen that and verified it with a voltmeter in an existing residence
i have over 30 years electrical experience in residential, commercial, industrial, and offshore drilling rigs

If you have lost both the PoCo neutral connection and your ground electrode connection, you probably have much bigger problems. I have seen systems maintain stable line to neutral voltage via earth return, but that possibility will depend on several factors like soil type, moisture and distance to the nearest PoCo ground electrode.

 

[dcg9381]

For UFER, it's unclear to me if the copper needs to be encased in flex conduit or can be left bare where it exits the concrete? I've seen it both ways. Seems like it'd be better to put it in flex.

I was researching this stuff and noticed that you can also do ground attachments to red iron (meaning the major structural posts) - as long as those posts eventually ground to a UFER:

 

[Half-fast eddie]

I was researching this stuff and noticed that you can also do ground attachments to red iron (meaning the major structural posts) - as long as those posts eventually ground to a UFER:

That’s assuming the anchor bolts are tied to the rebar. If they are wet-set, or drilled anchors … no good.