Okay, determining when lightning protection is not needed is a complex topic. The NEC doesn't explicitly state a distance where lightning protection is not required for communication cables between buildings. The need for lightning protection is based on a risk assessment, which involves many factors. However, we can analyze the concepts and relevant codes to give you a good understanding.

Key Considerations



Risk Assessment is Key

The NEC emphasizes performing a risk assessment. This is the most important factor.

NEC Chapter 8 - Communications Systems

Article 800 (General), 810 (Antenna Systems), 820 (CATV), 830 (Network-Powered Broadband Communications Systems), and 840 (Premises-Powered Broadband Communications Systems) cover communications wiring and grounding. These articles address protection of communication cables when protection is required.

Informational Note to 800.2

"Installing a cable in accordance with this article increases the likelihood that communication systems will not be subjected to voltages that could damage connecting equipment or increase the risk of fire or electric shock." This notes the purpose of the article, not a "no protection needed" exemption.

AHJ (Authority Having Jurisdiction)

Ultimately, the AHJ has the final say. They can require lightning protection even if a risk assessment seems to suggest it's not necessary. It's always best to consult with your local electrical inspector.

Cable Type and Application

The type of communication cable (e.g., Ethernet, coaxial, fiber optic) matters. Fiber optic cable is non-conductive and doesn't require lightning protection from direct strikes or induced voltage.

Grounding and Bonding

Proper grounding and bonding are crucial, regardless of whether lightning protection is installed. Effective grounding and bonding systems can help minimize the impact of surges.

NEC Relevant Sections and Related Considerations



NEC 800.44 Bonding and Grounding

This is a critical section for communication cables that must be followed, particularly in areas subject to lightning.

NEC 810.15 Antenna Discharge Units

Required for antenna systems. This section indirectly relates because it demonstrates the need to protect systems subject to induced lightning voltages.

NEC 250 Grounding and Bonding

Overall good grounding practices will improve the system's resilience to transients.

Why There's No Simple Distance Rule

Lightning is unpredictable. A nearby strike can induce voltage surges in cables that travel a considerable distance. Factors influencing induced surges include:

Soil Conductivity

Affects how electrical energy dissipates into the ground.

Local Lightning Strike Density (Isokeraunic Level)

Areas with more frequent lightning strikes require more protection.

Building Construction

Steel-framed buildings can act as better lightning conductors than wood-framed structures, potentially increasing risk to equipment connected to communication cables.

Grounding Systems

Adequacy and interconnection of grounding systems in both buildings are crucial.

Proximity to Other Structures

Tall structures or trees near the cable run can influence lightning strike patterns.

General Guidelines and Best Practices (NOT a substitute for a risk assessment)


Fiber Optic Cable

If feasible, use fiber optic cable. It's non-conductive and inherently immune to induced surges.2.

Buried Cable

Direct burial of the communication cable provides better protection than aerial cable runs. If buried, the cable should be grounded at both ends (following NEC requirements).3.

Surge Protective Devices (SPDs)

Install SPDs at the point where the communication cables enter each building. Coordinate the SPDs with the type of communication equipment being protected.4.

Bonding

Ensure all metallic components of the communication system are properly bonded to the building's grounding electrode system.5.

Consult with a Lightning Protection Specialist

A qualified lightning protection system installer can conduct a thorough risk assessment and recommend appropriate protection measures.

In Summary

There is no specific distance mentioned in the NEC that exempts communication cables between buildings from needing lightning protection. A comprehensive risk assessment is essential to determine the need for lightning protection. The AHJ has the final authority. Fiber optic cable is inherently more resistant to lightning-related issues. Proper grounding and bonding are always critical. Consider SPDs where cables enter buildings.

Recommendation


Consult with a qualified electrical engineer or lightning protection specialist

They can perform a risk assessment specific to your location and situation.2.

Check with your local AHJ

They may have specific requirements for lightning protection in your area.3.

Consider using fiber optic cable

It's the most reliable way to avoid lightning-induced problems.4.

Implement robust grounding and bonding practices per NEC 250 and the relevant sections in Article 800. Flag for review