Understanding NEC Article 200: Use and Identification of Grounded Conductors

Introduction:
National Electrical Code (NEC) Article 200 provides critical guidelines for the identification and proper use of grounded conductors in electrical systems. Grounded conductors play a crucial role in ensuring the safe and effective operation of electrical systems by preventing electrical shock hazards and maintaining system integrity. This article outlines the key provisions of NEC Article 200, covering its scope, general rules, identification methods, and specific scenarios involving grounded conductors.

1. Scope of Article 200 (Section 200.1)

NEC Article 200 governs three main areas related to grounded conductors:

• Identification of terminals
• Use of grounded conductors in premises wiring systems
• Proper identification of grounded conductors

This article does not provide definitions for “Grounded Conductor,” “Equipment Grounding Conductor,” or “Grounding Electrode Conductor”; instead, it references NEC Article 100 for these definitions.

2. General Requirements (Section 200.2)

NEC Article 200 establishes that grounded conductors must comply with certain insulation and continuity requirements.

• Insulation (Section 200.2(A)):
• For systems operating at 1,000 volts or less, grounded conductors must have suitable insulation rated for the system’s voltage.
• In systems with solidly grounded neutral conductors operating at over 1,000 volts, insulation must meet or exceed 600 volts, as specified in NEC Article 250.184(A).
• Continuity (Section 200.2(B)):
  Grounded conductors must maintain electrical continuity independent of their connection to a metal enclosure, raceway, or cable armor. Grounded conductors must not rely on these connections for continuity. Instead, they must be connected to a designated terminal or busbar for grounded conductors.

3. Connection to Grounded System (Section 200.3)

Grounded conductors within a premises wiring system must be electrically connected to the grounded conductor of the supply system. This ensures a continuous and common grounded system across the entire premises.

An exception to this rule allows for distributed resource generation systems, such as photovoltaic or fuel cell systems, to be connected to the premises wiring without a grounded conductor, provided the utility system or premises wiring includes one.

4. Neutral Conductors (Section 200.4)

Neutral conductors are closely related to grounded conductors, though they are not always the same.

• Installation (Section 200.4(A)): Neutral conductors must not be shared between multiple branch circuits or feeder conductors unless specifically allowed by the NEC. Each circuit must have its own neutral conductor.
• Multiple Circuits (Section 200.4(B)): When neutral conductors from multiple circuits are installed in the same enclosure, they must be grouped or identified to match the associated ungrounded circuit conductors. There are exceptions, such as when conductors enter through unique cable or raceway assemblies that make identification obvious.

5. Identifying Grounded Conductors (Section 200.6)

Grounded conductors must be clearly identified to ensure proper installation and safety.

• Sizes 6 AWG or Smaller (Section 200.6(A)):
  Grounded conductors must have a continuous white or gray outer finish or be marked with white or gray stripes. In some cases, they may use tracer threads or be identified by markings at terminations.
• Sizes 4 AWG or Larger (Section 200.6(B)):
  Grounded conductors sized 4 AWG or larger must also be identified with a white or gray outer finish or by white or gray markings at their terminations. These markings must encircle the conductor insulation, ensuring easy identification during installation.
• Flexible Cords (Section 200.6(C)):
  Grounded conductors within flexible cords must be identified with a white or gray outer finish. Flexible cords are often used for connecting appliances and equipment.
• Grounded Conductors in Systems of Different Nominal Voltage (Section 200.6(D)):
  Grounded conductors from different nominal voltage systems must be identified distinctly when they are installed in the same enclosure. This prevents confusion and ensures proper connection to the correct system.
• Multiconductor Cables (Section 200.6(E)):
  The grounded conductor within a multiconductor cable must have a continuous white or gray outer finish. For larger conductors, alternative identification methods, such as ridges on the cable, are permitted.

6. Insulation of White or Gray Conductors (Section 200.7)

White or gray conductors are typically reserved for grounded conductors, except in specific situations. For circuits operating at 50 volts or more, white or gray insulation can be re-identified for use as an ungrounded conductor through methods such as marking tape or painting at visible terminations. This helps to prevent confusion with grounded conductors.

7. Identifying Terminals (Sections 200.9 and 200.10)

Terminals intended for grounded conductors must be identified by a white or silver color. Polarized plugs, receptacles, and cord connectors must also have a white or silver terminal, or be marked accordingly. This is to ensure proper connection and prevent the reversal of polarity, which can lead to dangerous situations.

8. Polarity of Connections (Section 200.11)

NEC Article 200 strictly prohibits the attachment of a grounded conductor to a terminal or lead in a manner that reverses the designated polarity. Proper identification of terminals and adherence to polarity guidelines are essential for system safety.

Conclusion:

NEC Article 200 provides a comprehensive framework for the use and identification of grounded conductors in electrical systems. Proper identification, insulation, and connection of grounded conductors are critical for preventing electrical hazards and ensuring system reliability. Adhering to the guidelines in NEC Article 200 helps electricians maintain safety and compliance in their installations.

This summary of NEC Article 200 should serve as a useful reference for understanding grounded conductor requirements. Always consult the latest version of the NEC for the most up-to-date information and specific details relevant to your work.