Ground Loop Under Concrete

[jbreting]

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]

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]

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.

 

[jbreting]

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

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.

 

[jim dungar]

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.

 

[jbreting]

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.

The replacement of the grounding conductors makes a lot of sense actually.

 

[jbreting]

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.

Yes, I am able to remain on the outside of the foundation except for one side.

 

[don_resqcapt19]

This is a design issue as the "ground loop" is not covered by the NEC.

 

[tom baker]

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

 

[roger]

What is earthing the the pumps and hand rails supposed to be achieving?

 

[jbreting]

What is earthing the the pumps and hand rails supposed to be achieving?

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]

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

Read 250.4(5), especially the last sentence.

 

[jbreting]

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

Read 250.4(5), especially the last sentence.

Thank you for pointing this out, I will look into this further and revise my design accordingly.

 

[roger]

You are welcome.

 

[don_resqcapt19]

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.

What insulation failure would result in the hand rails becoming energized? From the NEC Style manual:
likely to become energized = failure of insulation on