Grounding Study in Refinery

[Isaiah]

The Client wants a grounding study in order to "help determine the required number and type of ground rods required to meet the desired resistance level of 5 ohms, plant wide"....Is this a legitimate, realistic request for a system (refinery) governed by NEC?
For Utility High-Voltage Substations, step-touch is more critical (IEEE-80) but with refineries and chem plants we usually simply drove more rods when needed.
Thanks in advance.
Isaiah

 

[roger]

The Client wants a grounding study in order to "help determine the required number and type of ground rods required to meet the desired resistance level of 5 ohms, plant wide"....Is this a legitimate, realistic request for a system (refinery) governed by NEC?

Isaiah

No it is not, the NEC doesn't require a level at all after two rods are driven. You can drive rod after rod and maybe get to a certain value but tomorrow when the weather and soil conditions change it can be out the window.

Roger

 

[Isaiah]

No it is not, the NEC doesn't require a level at all after two rods are driven. You can drive rod after rod and maybe get to a certain value but tomorrow when the weather and soil conditions change it can be out the window.

Roger

Thanks Roger - exactly my thoughts.

 

[JoeStillman]

I saw a request like this once. It came from a client who thought you needed extra-low resistance in order to be sure there was enough current to trip non-GFI breakers on a ground-fault. They applied ohm's law to the code-minimum 25 ohms and said 120V / 25Ω = 4.8 amps = no trip!. They needed to be persuaded that proper equipment grounding and especially, bonding were more important than lowering neutral-to-ground resistance.

Those green wires are really a redundant neutral in a fault-to-ground situation.