Ensuring Electrical Safety: The Importance of Arc Flash Studies, Short Circuit Analysis, and Coordination Studies

At Sol Rebel Power Systems, we prioritize the safety and reliability of the systems we engineer. A critical component of this commitment involves conducting comprehensive studies and implementing strategies to mitigate electrical hazards.

NEC Requirements for Arc Flash Labeling

The National Electrical Code (NEC) mandates specific labeling to alert personnel to potential arc flash hazards:

• Service and Feeder Equipment: In the 2023 NEC, Article 110.16(B) was updated to enhance safety measures. Previously, this requirement applied solely to service equipment rated 1,200 amperes or more. The 2023 revision expanded the scope to include both service equipment and feeder-supplied equipment rated 1,000 amperes or more in non-dwelling units. Additionally, the detailed specifications for nominal system voltage, available fault current, and clearing times were replaced with a requirement for the arc flash label to be in accordance with applicable industry practice and to include the date the label was applied. 

These changes align the NEC more closely with industry standards, such as NFPA 70E, ensuring a consistent approach to arc flash labeling and enhancing worker safety.

Coordination Studies for Enhanced System Reliability

Proper coordination between inverter feeder circuit breakers at the AC combiner panel and upstream main breakers or fuses is essential. This ensures that in the event of a fault on a feeder circuit to an inverter, the feeder breaker trips before the main breaker, maintaining system uptime. However, achieving this coordination must be balanced with the need to reduce arc energy to enhance safety.

Balancing Coordination and Arc Energy Reduction

Reducing arc energy can be accomplished by lowering breaker settings to enable faster tripping or by using fast-acting (current-limiting) fuses. However, setting the main breaker's trip settings too low can hinder proper coordination with downstream inverter feeder breakers. Therefore, a careful analysis is required to balance system protection and safety effectively.

Considerations for Medium Voltage Interconnections

In larger-scale projects with medium voltage (up to 34.5 kV) utility interconnections, the main "customer-owned" protective relay at the point of interconnection must coordinate with the upstream utility recloser. The recloser settings must also protect the transformer and be configured to trip before the main generator step-up (GSU) transformer fuses blow, as resetting a recloser is more straightforward than replacing fuses.

Implementing the "second harmonic blocking" feature in SEL relays can effectively ignore GSU transformer inrush currents, allowing for lower instantaneous trip settings. This significantly reduces incident arc energy and improves worker safety, all while maintaining proper coordination across protective devices.

Additionally, recloser overcurrent settings must be set high enough to prevent nuisance tripping under normal operating conditions and should coordinate with the main breaker(s) on inverter aggregation switchboard(s) and the inverter feeder breakers. Achieving this level of coordination is challenging, particularly in complex systems where multiple protective devices interact. Detailed information on the breaker models and settings available is required.

Looking Ahead

As of now, there are no specific indications of further changes to NEC Article 110.16(B) in the upcoming 2026 code revision. However, staying informed about potential updates is crucial for compliance and safety. Engaging with industry publications and participating in professional forums can provide valuable insights into forthcoming code modifications and best practices.

By conducting thorough arc flash, coordination and short circuit studies, and implementing effective arc energy reduction techniques, Sol Rebel Power Systems ensures that the projects we design are both safe and reliable. Our commitment to adhering to NEC requirements and employing advanced protective strategies underscores our dedication to excellence in solar engineering.