Comprehensive Analysis of Sizing Equipment Grounding Conductors in Parallel
This article explores the technical justification for sizing equipment grounding conductors (EGCs) larger than ungrounded conductors in electrical raceway installations. It emphasizes the role of impedance and the behavior of fault currents, noting that fault current, while primarily following the path of least impedance, actually disperses across all available paths back to the source. The article also highlights how installed devices and electrical equipment on ungrounded conductors increase their impedance.
Introduction: The sizing of conductors in electrical installations, particularly in raceways, is critical for safety and functionality. Special attention is needed for equipment grounding conductors (EGCs), which may need to be larger than ungrounded conductors. This necessity arises from the different impedance characteristics of these conductors and the dynamics of fault currents in electrical systems.
Impedance in Electrical Conductors: Impedance in electrical engineering is the opposition of a circuit to current flow when voltage is applied. It combines resistance with inductive and capacitive reactance. Ungrounded conductors inherently have impedance due to material resistance and inductive reactance. This impedance is increased by additional devices and equipment, adding more inductive and capacitive components. In contrast, EGCs are designed for lower impedance, achieved by minimizing length and reducing inductive reactance exposure.
Fault Current Behavior and Implications: Fault current primarily follows the path of least impedance but also spreads across all available paths back to the source. This dispersion is fundamental in electrical fault conditions. The increased impedance in ungrounded conductors can limit fault current magnitude, affecting protective device operation. Therefore, EGCs must maintain low impedance, often requiring them to be larger than ungrounded conductors to handle fault currents effectively.
Sizing of Equipment Grounding Conductors: Electrical codes provide guidelines for EGC sizing, considering impedance and the need for a low-impedance grounding path. Sizing involves assessing conductor material, insulation type, length, and connected load nature. Scenarios, where EGCs should be larger than ungrounded conductors, are analyzed, focusing on impedance considerations and fault current behavior.
2026 NEC First Draft Meetings (CMP5): In the 2026 National Electrical Code (NEC) revisions, the decision by Code Making Panel 5 stating that the equipment grounding conductor (EGC) never needs to be larger than the largest ungrounded conductor in any raceway when installed in parallel appears to be an oversight, particularly when considering the critical factors discussed earlier.
This declaration seems to neglect the intricate interplay between impedance and fault current behavior in electrical systems. As established, the impedance of ungrounded conductors increases with the addition of devices and equipment, which can limit the magnitude of fault current through these paths and potentially hinder the operation of protective devices. Consequently, EGCs must maintain a low impedance to ensure rapid detection and clearing of fault currents.
By not allowing the EGCs to be sized larger than the ungrounded conductors in certain scenarios, there is a risk of underestimating the impedance impacts and the multi-path nature of fault currents. Such a constraint could compromise the safety and efficiency of the electrical system, especially in complex installations where the dynamics of fault current dispersion and impedance variations are more pronounced.
Therefore, this decision by Code Making Panel 5 might not align with the principles of optimal electrical safety and functionality as detailed in the previous analysis.
Conclusion: This discussion underscores the critical nature of EGC sizing in electrical systems, particularly regarding ungrounded conductors. It highlights the importance of considering impedance and the multi-path nature of fault currents, reinforcing the need for appropriately sized EGCs for optimal safety and system performance.
This comprehensive analysis aims to enhance understanding of the importance of EGC sizing in electrical installations, focusing on raceway systems, and considering both impedance factors and the multi-path nature of fault currents for safety and efficiency.
Paul W. Abernathy, CMECP®
Electrical Code Academy, Inc.
CMP 5 Committee Member
