Current Conundrum: The Critical Need for Accurate Sizing Equipment Grounding Conductors in Parallel Installations

In parallel installations, the dynamics of ground fault current and the sizing of equipment grounding conductors (EGCs) are critical considerations for electrical safety. This becomes particularly significant in the context of ground faults and their impact on the electrical system.

Parallel Installation Dynamics In high-current applications, conductors are often run in parallel to distribute the electrical load. This setup involves separate sets of ungrounded (hot), neutral (if applicable), and EGCs for each parallel path.

Nature of Ground Faults A ground fault occurs when there's an unintended electrical connection between an ungrounded conductor and a conductive path to the ground, in this case, "ground" being the reference point of zero voltage at the source. This creates an alternative pathway for electrical current, bypassing the intended load.

Distribution of Ground Fault Current In the event of a ground fault, the current seeks to return to its source, typically the transformer or generator. The current flows through all available paths, with the division governed by the impedance of each path.

Higher Current in Individual Raceways In each raceway of a parallel installation, the ground fault current can exceed the normal carrying capacity of the ungrounded conductors. This situation arises as the fault current from the entire system converges into these pathways, particularly if the EGCs have lower impedance compared to other paths.

Necessity of Increasing EGC Size Given the potential for higher fault current in each raceway, EGCs must be properly sized. An undersized EGC may not be able to safely carry this high fault current, necessitating EGCs that are larger than the ungrounded conductors to ensure safe and effective fault current handling.

Safety and Compliance Implications Proper sizing of EGCs in parallel installations is critical for safety. It ensures that even during a ground fault, the fault current is effectively and safely returned to the source, preventing hazards like electrical fires or equipment damage. Adhering to electrical codes and standards is vital in this regard.

Conclusion The complexities of ground fault current flow in parallel installations necessitate careful consideration in the sizing of EGCs. The recommendation by Code Making Panel 5 in the first draft of the 2026 NEC, suggesting that the EGC never needs to be larger than the largest ungrounded conductor in each raceway when installed in parallel, overlooks a crucial safety aspect. Not allowing the EGC to be sized larger than the ungrounded conductors in these scenarios could lead to an undersized EGC, presenting a significant hazard. An undersized EGC, unable to handle the high fault current, could overheat, become compromised, or fail, leading to potential electrical fires, equipment damage, or other hazardous conditions. Therefore, sizing EGCs appropriately, considering their potential need to be larger than the ungrounded conductors, is critical for maintaining safety and compliance in electrical installations, especially in complex configurations like parallel installations.

This comprehensive analysis highlights the need for meticulous attention to the sizing of EGCs in parallel installations to ensure the safety and functionality of electrical systems.

Paul W. Abernathy, CMECP®

Electrical Code Academy, Inc.

CMP 5 Committee Member