Concrete encased electrode?

[sei3retired]

Why does the electrode have to be in the footing or foundation? I put a 20 foot rebar in a concrete sidewalk and the inspector turned the job down! Al

 

[roger]

Read 250.52(3).

Please update your profile to include what trade you are retired from.

Thank you

 

[Dennis Alwon]

Why does the electrode have to be in the footing or foundation? I put a 20 foot rebar in a concrete sidewalk and the inspector turned the job down! Al

It is all about moisture. Under a sidewalk is not likely to be that wet compared to a footing on a building. What is the concrete encase electrode for.

 

[don_resqcapt19]

In addition to the moisture, mentioned by Dennis, it is also the contact pressure between the concrete and the earth. Where the concrete is supporting a building or structure, there is more contact pressure.

 

[tom baker]

The original study by Herb Ufer in the mid 60’s was using 1/2 rebar in a concrete footing. He later added 20 ft of #4 copper wire. This became known as the ufer ground. His intent was to find a permanent, low cost, low resistance ground. A sidewalk does not meet the requirements for a ufer ground, and it is less permanent than a building foundation. And as pointed the ufer works well due moisture and ground pressure

 

[tom baker]

Please review 250.52 A 3.

 

[kwired]

I will add that in areas where it gets cold the footing is normally below the frost line which likely will effect resistance on a seasonal basis on a shallow item like a typical sidewalk.

 

[Sea Nile]

Not to mention the electrode grounding conductor is supposed to be as short as possible with as few bends or sharp turns as possible.

 

[kwired]

Not to mention the electrode grounding conductor is supposed to be as short as possible with as few bends or sharp turns as possible.

That might be good design but I don't believe NEC addresses this.

 

[Sea Nile]

That might be good design but I don't believe NEC addresses this.

Dang, I could have swore it was in the NEC, but I couldn't find it.
Ok, so I watched Mike Holt's Grounding and Bonding DVD and I've watched his understanding the NEC volume 1 at least twice and he said that due to the skin effect of induced voltage, the EGC needs to be as short as possible and with as few bends as possible due to the high frequency of a lightning strike it reacts like very high frequency high voltage AC.
I'm surprised the NEC doesn't address it. But thanks, you saved me from embarrassing myself in a future real life conversation

 

[hillbilly1]

Dang, I could have swore it was in the NEC, but I couldn't find it.
Ok, so I watched Mike Holt's Grounding and Bonding DVD and I've watched his understanding the NEC volume 1 at least twice and he said that due to the skin effect of induced voltage, the EGC needs to be as short as possible and with as few bends as possible due to the high frequency of a lightning strike it reacts like very high frequency high voltage AC.
I'm surprised the NEC doesn't address it. But thanks, you saved me from embarrassing myself in a future real life conversation

I think you’re thinking of TVSS’s, they have that requirement to be the most effective.

 

[kwired]

Dang, I could have swore it was in the NEC, but I couldn't find it.
Ok, so I watched Mike Holt's Grounding and Bonding DVD and I've watched his understanding the NEC volume 1 at least twice and he said that due to the skin effect of induced voltage, the EGC needs to be as short as possible and with as few bends as possible due to the high frequency of a lightning strike it reacts like very high frequency high voltage AC.
I'm surprised the NEC doesn't address it. But thanks, you saved me from embarrassing myself in a future real life conversation

I think most what you mentioned is common practice or even requirement for lightning protection system conductors but not for the grounding electrode conductor particularly on 1000 volts and less systems.

 

[infinity]

Dang, I could have swore it was in the NEC, but I couldn't find it.

There is something similar mentioned here in the IN:

250.4(A) Grounded Systems.
250.4(A)(1) Electrical System Grounding.
Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the
voltage to earth during normal operation.
Informational Note No. 1: An important consideration for limiting the imposed voltage is the routing of bonding and grounding electrode conductors so that they are not any longer than necessary to complete the
connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided. Informational Note No. 2: See NFPA 780-2017, Standard for the Installation of
Lightning Protection Systems, for information on installation of grounding and bonding for lightning protection systems.

 

[Sea Nile]

Fast forward to time 31:10 and watch to 32:30 or longer if you want.

There may be more references to making it short and as little bends as possible but I don't wast to watch the whole 1 hour and 13 minute video right now

 

[Sea Nile]

There may be more references to making it short

In fact I know there are. He addresses it more in depth somewhere else because he talks about the skin effect

 

[kwired]

There is something similar mentioned here in the IN:

Just like voltage drop limitations that some think are a code requirement but for most part are just a suggestion. An energy code might make the VD limitation something you are required to follow though. May be just good design practice in some situations, others it doesn't matter all that much.

 

[jaggedben]

There is something similar mentioned here in [250.4(A)(1) info note #1]:

Beat me to it.

 

[tom baker]

That might be good design but I don't believe NEC addresses this.

It’s there as an IN

 

[jxofaltrds]

Why does the electrode have to be in the footing or foundation? I put a 20 foot rebar in a concrete sidewalk and the inspector turned the job down! Al

Did he turn it down because of the size of the rebar or because the sidewalk isn't part of the structure?

Question? How much moisture is in lava?

 

[jaggedben]

Did he turn it down because of the size of the rebar or because the sidewalk isn't part of the structure?

Probably because 250.52(3), cited above, specifically calls for the CEE to be in a 'foundation or footing'.