Ground Ring or Ground Rod Around Low Voltage Concrete Pad With Fencing

[Jackbenimble7]

Hello,

I'm a first time poster who has learned a lot from your forum discussion. I'd like to say thank you in advance for any answers you all may be able to provide.

I have a question regarding grounding electrical equipment on a concrete pad. We are installing low voltage electrical equipment (low voltage transformers, switchboards, etc). on concrete pads with a chain link fence around the pads. From my knowledge, all that is required to ground the pad is a copper ground rod. However, I am being given direction that due to the installation of the chain link fence, that I need to install a ground RING around the concrete pad. Generally this wouldn't be an issue, and we can install the ground ring going forward. However, in this case, the concrete has already been poured, and it would require a lot of time and money to go back and install a ground ring instead of a single ground rod. Does anyone know if there are code requirements on grounding concrete pads with fencing around it?

I have gone through the IEEE 80, but I believe that information is not applicable to low voltage. I've also looked through the NEC, but there isn't really any information that specifies when to use a ground rod vs a ground ring.

Has anyone run into this issue before or know where I can look for guidance?

Thank you,

Jack

 

[ActionDave]

You are at the mercy of whomever is writing the specs.

 

[ron]

IEEE 80 is a guide, not a code. Some invoke IEEE 80 in specs, even for low voltage.

Some people forget that 250.190 and 250.194 (new to NEC-2014) apply to Systems and Circuits of over 1000 Volts

 

[Jackbenimble7]

Let me ask you this, would a ground ring actually be more effective than a ground rod in this scenario?

 

[jaggedben]

Let me ask you this, would a ground ring actually be more effective than a ground rod in this scenario?

More effective at doing what? Creating an electrical connection to ground? Probably by some measure yes. Protecting people or property? Less likely.

How big an area are we talking about?

 

[Jackbenimble7]

The area is about 10' by 10'. The pad itself is 6'x8'.

It is my understanding that there are two faults to be concerned about in this scenario, the touch fault and step fault.

The step fault will be the same regardless. If you step somewhere when the transformer is experiencing a ground fault, the extra grounding will not help you.

However, the touch fault is what I am concerned about. If you touch the fence or touch the transformer and the fence while the transformer is undergoing a ground fault, I would like the person to be as protected as possible.

Because the area is so small, I believe we would be looking at hundreds of ground rods to bring down the potential touch fault. At this point, I'm thinking of creating a ground ring around the fence with a single ground rod at the concrete pad. I can then bond these two together to create single grounding device.

Any opinions?

 

[jim dungar]

The area is about 10' by 10'. The pad itself is 6'x8'.

If there was no fence at all, would a ground ring even be discussed? Padmount and other enclosed equipment is regularly installed with nothing more than ground rod connections.

How is the fence going to become energized? Are there overhead conductors which might fall?

 

[jaggedben]

My thought is that if you're concerned about people touching the fence you should bond the fence. (If the fence has metal supports stuck into the ground, it will probably act as an additional grounding electrode, albeit not one that qualifies under the NEC unless one of the supports goes 10ft down.)

 

[Smart $]

Sounds like someone doesn't know the difference between bonding and earthing. :happyyes:

(I see jb brought up bonding while I was typing.)

 

[Jackbenimble7]

If there were no fence, a ground ring would not even be discussed. My main concern is making sure the fence is safe to the touch. There aren't any power/transmission lines overhead, so I'm really just worried about fault current protection.

How can I bond the fence?

 

[Smart $]

...
How can I bond the fence?

Run a bonding jumper from the ground rod, perhaps... or from the ground bus in the transformer.

 

[petersonra]

If there were no fence, a ground ring would not even be discussed. My main concern is making sure the fence is safe to the touch. There aren't any power/transmission lines overhead, so I'm really just worried about fault current protection.

How can I bond the fence?

If it is just about fault current, a ground rod or ring serves no real purpose. You can't use the earth as part of a ground fault path.

Just bring an EGC out and connect it to the fence if all you care about is ground fault protection.