You are correct. As far as I can tell, the NEC (National Electrical Code) does not explicitly mandate a ground ring around aircraft hangars.Here's why and where the requirements are likely coming from: NEC (NFPA 70)

The NEC focuses on the safe installation of electrical wiring and equipment. While it addresses grounding and bonding in general, it doesn't single out specific occupancy types like aircraft hangars for mandatory ground rings. NEC Article 513 covers Aircraft Hangars, but it mainly addresses hazardous (classified) locations and specific wiring methods.

Engineering Design and Standards (e.g., lightning protection, specific project requirements)

The requirement for a ground ring in an aircraft hangar is almost certainly driven by engineering design considerations, industry best practices, and potentially specific project requirements. Here are a few potential reasons for a ground ring:

Lightning Protection

If the hangar is equipped with a lightning protection system (LPS), a ground ring is a very common component of that system. Lightning protection standards (like NFPA 780, Standard for the Installation of Lightning Protection Systems) often recommend or require ground rings to dissipate lightning energy safely into the earth.

Equipotential Bonding

Ground rings are excellent for creating an equipotential plane, reducing potential differences within the hangar. This is crucial to prevent dangerous touch potentials, especially when dealing with aircraft and sensitive electronic equipment.

Radio Frequency (RF) Shielding

In some cases, a ground ring can contribute to RF shielding, which might be important if the hangar houses sensitive avionics or communication equipment.

Owner Requirements/Insurance

The hangar owner or their insurance company might have specific requirements for grounding and bonding that necessitate a ground ring.

Military/Government Standards

If the hangar is on a military base or is a government facility, there may be specific grounding and bonding requirements in applicable military or government standards that go beyond the NEC.

NFPA 409 (Standard on Aircraft Hangars)

This standard deals with fire protection in aircraft hangars. While it doesn't mandate a ground ring, it does emphasize grounding and bonding to reduce the risk of static electricity buildup and ignition of flammable vapors. A ground ring could be a means of complying with NFPA 409's general grounding requirements.

In summary

While the NEC doesn't explicitly say "all aircraft hangars must have a ground ring," it does provide the general requirements for grounding and bonding of electrical systems. The specific requirement you are seeing is likely coming from one or more of the following: A lightning protection standard (NFPA 780). An engineering design based on the specific needs of the hangar (e.g., equipotential bonding, RF shielding). Owner or insurance company requirements. Applicable military or governmental standards. General compliance with NFPA 409.

Recommendation



Review the Project Specifications

The most important thing is to review the original project specifications and drawings. They should clearly state the reason for the ground ring and reference the applicable standard (e.g., NFPA 780).

Consult the Design Engineer

Talk to the electrical engineer or the lightning protection system designer who specified the ground ring. They can explain the rationale behind the requirement.

Check for Local Amendments: While unlikely, it's always a good idea to check with the local authority having jurisdiction (AHJ) to see if there are any local amendments to the NEC or other regulations that might apply.By understanding the specific reasons for the ground ring, you can ensure that it is installed correctly and meets the intended purpose. Flag for review