You're right to be leery. While the consultant isn't necessarily wrong, applying IEEE 80 and requiring a full-blown grounding grid might be overkill for your specific application. Here's a breakdown of why and what you should consider

Understanding the Concern: Step and Touch Potential
Step Potential

The voltage difference a person could be exposed to by stepping a meter apart near a ground fault.

Touch Potential

The voltage difference a person could be exposed to by touching a grounded object (like a metal enclosure) during a ground fault.

Why it matters

High voltages during a ground fault can be dangerous or even fatal. A proper grounding system is designed to limit these voltages to safe levels.

Why IEEE 80 is Normally for Substations



High Fault Currents

Substations handle very large fault currents (thousands of amps) due to their direct connection to the power grid.

High-Voltage Equipment

Substations contain high-voltage transformers, switchgear, and other equipment where a ground fault could release a significant amount of energy.

Frequent Public Access

While substations are usually fenced, there's a higher risk of unauthorized access compared to a typical tunnel ventilation building.

Why it Might be Needed (or Not) in Your Case



Fault Current Availability

This is the key factor. What is the maximum available fault current at your 2.4 kV incoming service? The higher the fault current, the higher the risk of dangerous step and touch potentials. Your utility should be able to provide this information.

Soil Resistivity

This also plays a crucial role. High soil resistivity makes it harder to dissipate fault current, leading to higher voltage gradients. A soil resistivity test is essential for any grounding analysis.

Building Construction

Is the building primarily steel-framed and grounded? Are there extensive buried metallic structures (pipes, conduits) that could act as ground conductors? These existing elements might provide some grounding benefit.

Human Exposure

Who has access to the equipment? Are there public areas nearby? The more people potentially exposed, the more conservative the grounding design should be.

Equipment Sensitivity

Are there sensitive electronic devices that could be damaged by high ground potentials?

Code Requirements

While IEEE 80 is a standard, it's not always a code requirement. Check your local electrical codes (NEC, state, or local amendments) to see what specific grounding requirements apply to your facility type and voltage level.

The utility's grounding

Do they specify what your grounding system must do? If they do, it's likely related to their system protection.

Questions to Ask the Consultant


Fault Current Calculations

"Can you provide the specific calculations showing the expected fault current at our 2.4 kV service entrance? What are the assumptions used?"2.

Soil Resistivity Measurements

"Will you be performing soil resistivity testing at our site? What methods will you use?"3.

Code References

"What specific code sections or regulations require this level of grounding for our type of facility?"4.

Alternative Solutions

"Are there less extensive, more cost-effective grounding solutions that could achieve acceptable safety levels, given our specific fault current and site conditions?" For example:

Grounding Electrode System (GES)

A simpler grounding system using ground rods, buried conductors, and connections to building steel might be sufficient.

Equipment Grounding Conductors (EGCs)

Properly sized EGCs run with all power circuits and bonded to equipment enclosures are essential.

Concrete Encased Electrode (Ufer Ground)

Rebar in the footing of the foundation, bonded together and connected to the service ground.5.

Justification

"What are the specific step and touch potential calculations that demonstrate the need for a grounding grid? What are the acceptable voltage limits you are using for your calculations?"6.

Cost

Get a cost breakdown for the grounding grid and compare it to other options.

What You Should Do


Get the Fault Current

Request the available fault current from your utility company at the 2.4kV incoming service. This is crucial.
2.

Require Soil Testing

Insist on soil resistivity testing. It's a fundamental input for any grounding analysis.3.

Review the Code

Carefully review the applicable electrical codes (NEC and local amendments) to determine the minimum grounding requirements for your facility.4.

Get a Second Opinion (Maybe)

If you're still unsure after talking to the consultant, consider getting a second opinion from another qualified electrical engineer with experience in grounding systems. This can be especially helpful if the consultant's recommendations seem disproportionately expensive.5.

Document Everything

Keep detailed records of all discussions, calculations, test results, and grounding system designs. This will be important for future maintenance, inspections, and potential liability concerns.

In summary, a full IEEE 80 grounding grid might be necessary, but it's not a given. You need to understand the fault current, soil conditions, building construction, and local code requirements to make an informed decision. Question the consultant thoroughly and ensure their recommendations are based on solid data and a realistic assessment of the risks. Good luck! Flag for review