Ground Loop Under Concrete

J

jbreting

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Location
Lakeland, FL
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EE
I am designing a ground loop system for two 5000 gal tanks at a slag plant. I am restricted to how far from the tank I can place the ground wire and rods. It turns out I have to place them under the foundation the tanks are on.

Well, I am referencing some drawings from the previous engineer and he had a note: " Ground conductors that run below slab shall be installed prior to concrete pour and shall be run in 1" schedule 40 PVC conduit". Could someone tell me the reason why it needs to be ran in conduit and the NEC code that states this?
 
tom baker

tom baker

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Bremerton, Washington
What is in the tanks?
What is the purpose of the ground loop?
Perhaps the PVC is to protect the wire going thru the slab to the earth
The NEC may not apply, but there are other codes that may
 
synchro

synchro

Senior Member
Location
Chicago, IL
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EE
I'm speculating, but in addition to physical protection, they may want to be able to isolate the effectiveness of individual parts of the grounding system during testing. Embedding the conductors in concrete would complicate this.
Another possible reason is that the PVC conduit would facilitate replacement of the grounding conductors if necessary.
 
J

jbreting

Member
Location
Lakeland, FL
Occupation
EE
tom baker said:
What is in the tanks?
What is the purpose of the ground loop?
Perhaps the PVC is to protect the wire going thru the slab to the earth
The NEC may not apply, but there are other codes that may
Click to expand...
The purpose of the ground loop is to ground the pumps that rest on top of the tanks as well as the hand rails and tanks themselves. The tanks just hold water.
 
J

jim dungar

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I would think the PVC is only located where ever the conductor passes through the slab and not for the entire distance of the loop. The OP statement is ambiguous in this regard.
 
J

jbreting

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Location
Lakeland, FL
Occupation
EE
synchro said:
I'm speculating, but in addition to physical protection, they may want to be able to isolate the effectiveness of individual parts of the grounding system during testing. Embedding the conductors in concrete would complicate this.
Another possible reason is that the PVC conduit would facilitate replacement of the grounding conductors if necessary.
Click to expand...
The replacement of the grounding conductors makes a lot of sense actually.
 
tom baker

tom baker

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The EGC for the pumps provide the NEC required bonding. The ground loop provides no value in protecting against electric shock. The design is confusing grounding and bonding.

But as Don pointed out the ground loop is not required by the NEC, and is considered an auxilary electrode, and there are no code requirements on installation. It’s much the same as a ground rod at a metal lighting pole, frequently done, with no benefit to protect from electric shock
 
J

jbreting

Member
Location
Lakeland, FL
Occupation
EE
roger said:
What is earthing the the pumps and hand rails supposed to be achieving?
Click to expand...
Grounding the pumps is in accordance the 430.242 NEC 2023 where it states that:

"The frames of stationary motors shall be grounded under any of the following conditions:
(1) where supplied by metal-enclosed wiring
(2) Where in a wet location and not isolated or guarded
(3) If in a hazardous (classified) location
(4) If the motor operates with any terminal at over 150 volts
Where the frame of the motor is not grounded, it shall be permanently and effectively insulated from the ground. "

The grounding of the handrails is in accordance with 250.4 (4) NEC 2023:

"Normally non-current carrying conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path."

I know this is up for debate, and may not be absolutely necessary, but the handrails being grounded ensures that they are connected together and effective ground-fault current path is established.
 
roger

roger

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Fl
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Both of the sections you are referring to are for bonding and EGC connections, not earthing.

Read 250.4(5), especially the last sentence.
 
don_resqcapt19

don_resqcapt19

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Location
Illinois
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retired electrician
jbreting said:
Grounding the pumps is in accordance the 430.242 NEC 2023 where it states that:

"The frames of stationary motors shall be grounded under any of the following conditions:
(1) where supplied by metal-enclosed wiring
(2) Where in a wet location and not isolated or guarded
(3) If in a hazardous (classified) location
(4) If the motor operates with any terminal at over 150 volts
Where the frame of the motor is not grounded, it shall be permanently and effectively insulated from the ground. "

The grounding of the handrails is in accordance with 250.4 (4) NEC 2023:

"Normally non-current carrying conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path."

I know this is up for debate, and may not be absolutely necessary, but the handrails being grounded ensures that they are connected together and effective ground-fault current path is established.
Click to expand...
What insulation failure would result in the hand rails becoming energized? From the NEC Style manual:
likely to become energized = failure of insulation on
 
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