This is a complex question that requires careful consideration of multiple factors. While I can provide general guidance, it's crucial to consult with a qualified electrical engineer, corrosion expert, and local authorities (AHJ - Authority Having Jurisdiction) to ensure compliance with all applicable codes and regulations.Here's a breakdown of the considerations

Arguments for Grounding:
Electrical Safety

Even with an insulating coating, there's a potential for electrical faults in the level sensors or alarm panel to energize the tank. Grounding provides a low-impedance path to ground, allowing fault current to flow and tripping a circuit breaker or fuse, minimizing the risk of electric shock to personnel.

Static Electricity

Although less likely underground, static electricity can still build up in certain situations (e.g., from fluid movement). Grounding helps dissipate this charge, reducing the risk of sparks that could ignite flammable materials (depending on what's stored in the tank and the surrounding atmosphere).

Lightning Protection

Although underground, lightning strikes nearby can induce voltage in underground metallic objects. Grounding the tank can help mitigate the effects of these induced voltages.

Fault Current Return Path

If there is ever an electrical fault in equipment connected to the tank or any metallic piping associated with the tank, a grounding system provides a known, reliable return path for the fault current. This helps ensure that overcurrent protection devices (breakers, fuses) operate quickly and safely.

Manufacturer's Recommendations

Check the manufacturer's specifications for the tank, level sensors, and alarm panel. They may specify grounding requirements.

Arguments Against Grounding (or Modifications to Grounding)



Insulating Coating

The polyurethane coating is designed to electrically isolate the tank from the surrounding soil, theoretically preventing corrosion. Grounding the tank could compromise the coating's effectiveness by creating a path for stray currents to flow and concentrate at coating defects, accelerating corrosion.

Galvanic Corrosion

If the tank is directly connected to other metallic structures that are grounded, it could create a galvanic cell. The tank material might become anodic (corrode) relative to the other structures.

Code Exceptions/Clarifications

Some codes may offer exceptions or clarifications regarding grounding requirements for tanks with approved insulating coatings specifically designed for corrosion protection. This is highly dependent on the specific code.

Codes and Standards to Consider (Examples - Consult Local AHJ)



NFPA 70 (National Electrical Code - NEC)

Article 250 covers grounding and bonding requirements. Specifically, review sections related to equipment grounding, separately derived systems (if applicable), and grounding electrode systems. Pay close attention to the definitions of "grounded" and "bonded".

API Standards

The American Petroleum Institute (API) has standards that may apply, depending on the substance stored in the tank. Look for standards related to corrosion control and electrical safety for underground storage tanks. API 545: Recommended Practice for Lightning Protection of Aboveground Storage Tanks for Flammable Liquids is a common reference. Even though the tank is underground, some principles might still apply.

NACE International (now AMPP - Association for Materials Protection and Performance)

NACE provides standards and guidelines for corrosion control. They may have recommendations regarding grounding and its impact on corrosion protection systems.

Local Building and Electrical Codes

These are the most important codes to follow, as they have jurisdiction over your specific location. Contact your local building and electrical inspectors to determine the specific requirements.*

Environmental Regulations

State and federal environmental regulations related to underground storage tanks (USTs) may indirectly impact grounding requirements by specifying corrosion protection standards.

Recommendations


Consult a Qualified Electrical Engineer

A licensed electrical engineer with experience in grounding and bonding systems is essential. They can perform a thorough assessment of the project, taking into account the specific details of the installation, the type of substance stored in the tank, and the applicable codes and standards.2.

Consult a Corrosion Expert

A NACE-certified (or AMPP equivalent) corrosion specialist can assess the potential impact of grounding on the corrosion protection system and recommend appropriate measures to mitigate corrosion risks.3.

Contact the Authority Having Jurisdiction (AHJ)

The local building and electrical inspectors are the final authority on code compliance. Submit your plans and ask for their guidance on grounding requirements.4.

Consider Supplemental Grounding

If grounding is deemed necessary, consider using supplemental grounding electrodes that are electrically isolated from the tank itself. These electrodes can provide a low-impedance path to ground without directly connecting to the tank and potentially compromising the coating.5.

Monitor and Maintain the Coating

Regularly inspect and maintain the polyurethane coating to ensure its integrity. Address any defects promptly to prevent corrosion.6.

Implement Cathodic Protection (if necessary)

Depending on the specific circumstances and the recommendations of the corrosion expert, consider implementing a cathodic protection system to further protect the tank from corrosion.

In summary, there is no simple "yes" or "no" answer. While the insulating coating complicates the situation, the need for grounding depends on a comprehensive assessment of electrical safety, corrosion risks, and applicable codes. Consult with qualified professionals and your local AHJ to determine the best course of action. Ignoring grounding requirements can create significant safety hazards and potential code violations. Flag for review