concrete encased electrode

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kstanton5

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I am currently wiring a fine arts center and i am perplexed as to why the electrical engineer of record would specify a 4/0 bare copper conductor for my concrete encased electrode when the NEC only reguires a #4 conductor?
 

raider1

Senior Member
Staff member
Location
Logan, Utah
It is quite common to see engineering specs that require a larger CEE than what 250.66(B) requires.

I have seen engineered specs and plans that show a 3/0 run to a single ground rod.:roll:

Chris
 
I believe a portion of the reason for larger size conductors in regards to the grounding electrode conductor, is the lack of understanding the function associated with this conductor. Engineers are taught differently than the electrician, some of the fundamentals of this industry. Couple that with the fear of litigation, and we see 4/0 Copper GEC to 8ft ground rods, etc...
 

kstanton5

Member
conrete encased electrode

conrete encased electrode

Thanks for the insight. Now for another question regarding the concrete encased electrode. After talking to the general contracter's superintendent,he has informed me that it is his companies policy to stub up a piece of rebar so that I may attach to it! After telling him that I do not want him to do this because then it is no longer concrete encased,he informs me that that is the way he has always seen it done and he has been doing this for 38 years! Any suggestions convincing him otherwise.
 

A/A Fuel GTX

Senior Member
Location
WI & AZ
Occupation
Electrician
I have the concrete guy stub a piece of rebar out from the footing. Then I go to the site and bend the rebar down so it will be below the poured floor level, attach my #4 and a listed clamp and tie it off to a form tie until I can get back to install the service.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I have the concrete guy stub a piece of rebar out from the footing. Then I go to the site and bend the rebar down so it will be below the poured floor level, attach my #4 and a listed clamp and tie it off to a form tie until I can get back to install the service.
This may be a violation since rebar degrades when exposed to soil. I had heard this but am not definite about it.
 

gndrod

Senior Member
Location
Ca and Wa
No Dennis.....The rebar and clamp end up embedded in the concrete floor.

In some jurisdictions, an inspection buyoff of the UFER in slab or footer with an encased bonding clamp is necessary. One problem with the NEC is that there is no mention of the UFER stub up used as a wired portion of the footer rebar form that must be a minimum of three inch encasement. Even though the 2" rule for using the rebar as the CEE, the wired in stub is a structural condition violation. IRC [R403.1.3.1] Are there any inspectors here that are aware of this requirement? I wonder how inspections are being bought off prior to the pour? rbj
 

raider1

Senior Member
Staff member
Location
Logan, Utah
IRC [R403.1.3.1] Are there any inspectors here that are aware of this requirement?

Yes, as a combination inspector I am aware of that section. That section deals with foundations with stem walls in seismic design catagories D0, D1 and D2. Here is what that section requires.

R403.1.3.1 Foundations with stemwalls. Foundations with stem walls shall have installed a minimum of one #4 bar within 12 inches of the top of the wall and one #4 bar located 3 inches to 4 inches from the bottom of the footing.

Chris
 

gndrod

Senior Member
Location
Ca and Wa
R403.1.3.1 Foundations with stemwalls. Foundations with stem walls shall have installed a minimum of one #4 bar within 12 inches of the top of the wall and one #4 bar located 3 inches to 4 inches from the bottom of the footing.

Chris

Thanks Chris, How would this be applicable in slab floor construction where the slab portion is used for the UFER and the floor thickness is the minimum 4"?
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Well here is the POV of an engineer who is guilty of this practice.

In the industry I work in we have engineering and installation practices to follow written by geeks like me. Makes life simple. The industry practices meet or exceed any code requirements. Basically we error on the side of caution, vs an EC POV of meeting the minimum (financial/code) requirement.

Now I do not say that to start any flaming, we just have different POV’s and interest at stake.
 
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gndrod

Senior Member
Location
Ca and Wa
Well here is the POV of an engineer who is guilty of this practice.

In the industry I work in we have engineering and installation practices to follow written by geeks like me. Makes life simple. The industry practices meet or exceed any code requirements. Basically we error on the side of caution, vs an EC POV of meeting the minimum (financial/code) requirement.

Now I do not say that to start any flaming, we just have different POV?s and interest at stake.

Hi Derek,

I know what you are saying and believe all trades on either side of the fence make for interesting questions to solutions. I am not looking to stir up any electrons with the cement guys, but their codes tend to open up questions like the UFER-structure combined application.

Another rebar question comes to mind as to the stub up tie minimum length to the footer rebar. (I.e. 24" minimum Lap splice [R511.7.1.3] for rebar UFER stub up tie-in.) The NEC has no mention for wire bonding in many areas. rbj
 

raider1

Senior Member
Staff member
Location
Logan, Utah
Thanks Chris, How would this be applicable in slab floor construction where the slab portion is used for the UFER and the floor thickness is the minimum 4"?

It wouldn't this section only deals with the required seismic reinforcing requirements for a footing and stem wall. Floor slabs are not footings. There are monolithic slabs that do incorporate a footing within the slab. Slab on grades with turn down footings are addressed in IRC section R403.1.3.2 for seismic design categories D0, D1 and D2.

R403.1.3.2 Slabs-on-ground with turned-down footings. Slabs-on-ground with turned-down footings shall have a minimum of 1 #4 bar at the top and bottom of the footing.

Exception: For slabs-on-ground cast monolithically with a footing, 1 #5 bar or 2 #4 bars shall be located in the middle third of the footing depth.

Chris
 

gndrod

Senior Member
Location
Ca and Wa
Floor slabs are not footings. There are monolithic slabs that do incorporate a footing within the slab.

Chris

Sorry for not being a little more specific. Occasionally a garage slab poured into a stemwall with ledge has a stub up in the floor. This is I believe a non-compliant use of a CEE due to less than the minimum encasement and the location of the stub up without protection.

This brings up conflict as a poor method for using the slab as an electrode encasement. Most installers do not include a protective raceway over the GEC in this method. Would you tag this particular lack of encasement thickness over grade configuration as unacceptable? rbj
 

raider1

Senior Member
Staff member
Location
Logan, Utah
Sorry for not being a little more specific. Occasionally a garage slab poured into a stemwall with ledge has a stub up in the floor. This is I believe a non-compliant use of a CEE due to less than the minimum encasement and the location of the stub up without protection.

This brings up conflict as a poor method for using the slab as an electrode encasement. Most installers do not include a protective raceway over the GEC in this method. Would you tag this particular lack of encasement thickness over grade configuration as unacceptable? rbj

The ACI 318 and 332 standards deal with the requirement for minimum concrete encasement for structural reinforcing bars.

I would fail a CEE that used #4 re-bar that did not meet the required concrete encasement of these standards as referenced in the building codes.

Chris
 

gndrod

Senior Member
Location
Ca and Wa
The ACI 318 and 332 standards deal with the requirement for minimum concrete encasement for structural reinforcing bars.

I would fail a CEE that used #4 re-bar that did not meet the required concrete encasement of these standards as referenced in the building codes.

Chris

Thanks Chris, I have run into this once before with the UFER being considered structural because of the interlacing to the floor mesh. rbj
 
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