Understanding NEC Article 215: Feeders

NEC Article 215 governs the installation and protection of feeders, which are the electrical conductors that run from the service equipment to various distribution points, such as branch-circuit panels or equipment within a building. Feeders are critical components in electrical distribution systems, serving as the main pathways that deliver power from the source to subpanels and other downstream systems. This article focuses on ensuring that feeders are installed correctly, sized appropriately, and protected from overcurrent to ensure safe and reliable operation of electrical systems.

Scope of Article 215

Article 215 applies to feeders operating at voltages not exceeding 1000 volts AC or 1500 volts DC. It addresses the installation, minimum size, and ampacity of feeder conductors, as well as the necessary protection mechanisms. Feeders that exceed these voltage levels are covered under other sections of the NEC.

Minimum Rating and Size of Feeders

One of the core principles of Article 215 is determining the appropriate size and ampacity of feeder conductors. The ampacity of feeder conductors must be based on the type of load being supplied, whether continuous or noncontinuous. Continuous loads, defined as loads running for three hours or more, generate more heat over time, requiring feeder conductors that can handle 125% of the continuous load plus the full noncontinuous load. This is critical to prevent overheating of the conductors and ensure that the system remains safe under operating conditions.

In some cases, adjustments or corrections are made to the conductor size based on the installation conditions, such as ambient temperature or the number of conductors bundled together. These adjustment factors must be taken into account to ensure that the feeder conductors can carry the required load without excessive voltage drop or overheating.

Voltage drop is another critical factor to consider in feeder installations. Excessive voltage drop can impair the efficiency and performance of electrical equipment, especially motors and lighting systems. Article 215 suggests limiting voltage drop to 3% for feeders and branch circuits combined, keeping the total voltage drop to no more than 5%. This helps ensure that equipment operates efficiently without excessive energy losses or performance issues.

Overcurrent Protection for Feeders

Feeders must be protected against overcurrent, which could occur if the current flowing through the conductor exceeds its rated capacity. Overcurrent protection is typically provided by circuit breakers or fuses installed at the supply end of the feeder. The overcurrent device must be sized to handle the continuous load plus 125% of the noncontinuous load.

This protection prevents feeder conductors from overheating and reduces the risk of electrical fires or damage to equipment downstream. In cases where the equipment used is rated for 100% of its capacity, the overcurrent protection can be sized to match the full load, without the additional 25% margin for continuous loads.

Feeders with Common Neutral Conductors

NEC Article 215 permits the use of a common neutral conductor for multiple sets of feeders. In such cases, the neutral conductor must be properly sized to carry the maximum unbalanced load from the feeders, and all conductors must be enclosed in the same raceway or enclosure to avoid issues like induction heating in metal raceways.

This common neutral arrangement can simplify installations and reduce material costs, but it requires careful consideration of the conductor’s ampacity and the loads being served to ensure proper operation and safety.

Grounded and Ungrounded Conductors

Proper identification of grounded and ungrounded conductors is essential for maintaining safety and preventing confusion in installations with multiple feeders. Grounded conductors, or neutral conductors, must be identified according to NEC Article 200, while ungrounded conductors must be identified by their phase and voltage system at termination points.

In systems with multiple nominal voltages, ungrounded conductors must be labeled or color-coded to indicate their specific voltage and phase, ensuring that electricians can easily identify and work with the correct conductors. This is especially important in large commercial or industrial installations where different voltage systems may coexist.

Ground-Fault Protection

Article 215 includes provisions for ground-fault circuit-interrupter (GFCI) protection for feeders. GFCI devices are essential for protecting personnel from electric shock by detecting ground faults and interrupting the circuit. Feeders can be equipped with GFCI protection to provide a higher level of safety for all downstream branch circuits connected to the feeder. This setup is often used in temporary installations, such as construction sites, where multiple circuits need protection from ground faults.

In addition to GFCI protection for personnel, NEC Article 215 also requires ground-fault protection of equipment (GFPE) for feeders rated at 1000 amperes or more. This protects electrical systems from damage due to ground faults by interrupting the current flow before it can cause excessive heating or equipment failure. Exceptions to this requirement exist for industrial processes where an interruption in power could create a more hazardous condition, or where protection is already provided on the primary side of a transformer feeding the system.

Surge Protection

Surge protection is another critical safety measure addressed in Article 215. Feeders supplying dwelling units, dormitories, hotels, motels, and nursing homes are required to have surge protection devices (SPDs) installed. These devices protect sensitive electronic equipment from transient overvoltages caused by lightning strikes, power surges, or switching events within the electrical system. Surge protection helps prevent costly damage to equipment and enhances the overall reliability of the electrical system.

Feeder Diagrams

In some installations, local authorities may require a detailed feeder diagram to be submitted before installation. This diagram includes important information such as the area being served, the total calculated load, demand factors, and the size and type of conductors being used. Having a clear and well-documented feeder plan ensures that the installation complies with NEC standards and meets the requirements of the authority having jurisdiction.

Special Provisions for Autotransformers and Tapped Circuits

Feeders derived from autotransformers are allowed under specific conditions outlined in Article 215. Autotransformers are often used to step voltage levels up or down, but they must have a grounded conductor connected to the supply system unless certain exceptions apply. For example, in industrial applications where only qualified personnel service the installation, an autotransformer may be used without connecting to a grounded conductor when transforming between 480 and 600 volts.

In some cases, ungrounded conductors can be tapped from grounded systems, allowing for two-wire circuits to be derived from systems that include a neutral conductor. This arrangement must include proper switching devices to disconnect both ungrounded conductors simultaneously when needed.

Conclusion

NEC Article 215 provides comprehensive guidelines for the safe and efficient installation of feeder circuits in electrical systems. By addressing the minimum size and ampacity of conductors, overcurrent protection, grounded and ungrounded conductor identification, and ground-fault protection, this article ensures that feeders are capable of delivering reliable power while minimizing the risk of electrical hazards.

Understanding and adhering to the requirements of Article 215 is critical for electricians, engineers, and inspectors involved in the design, installation, and maintenance of electrical systems. The article’s focus on conductor sizing, protection mechanisms, and special conditions for certain types of circuits helps create safe, code-compliant electrical installations that meet the needs of modern buildings and facilities.