What Is a Grounded Conductor? The Neutral Wire Explained

Answering Your Core Question: What is a Grounded Conductor?

A grounded conductor, most commonly known as the neutral wire, is a vital component of an electrical circuit intentionally connected to the earth. Defined in the National Electrical Code (NEC), its primary purpose is to serve as a return path for current, making it a current-carrying conductor under normal operating conditions. It completes the circuit back to the source, typically a center-tapped transformer. It is crucial not to confuse the grounded conductor vs grounding conductor; the latter, an equipment grounding conductor (EGC), is a safety wire that only carries current during a fault. Proper grounded conductor sizing is essential for safely managing the return current, especially the unbalanced load on neutral in multi-wire branch circuits. The rules governing its use, identification, and sizing are detailed extensively in NEC Article 200 and NEC Article 250, ensuring system stability and safety.

The Role of the Grounded Conductor in an Electrical System

In any AC electrical system, current requires a complete path to flow from the source, through the load, and back to the source. The system grounded conductor provides this return path. In a typical 120/240V single-phase service, the utility transformer’s secondary winding is center-tapped. This center tap is grounded at the transformer, establishing the wire connected to it as the grounded conductor, or neutral. This conductor is maintained at or near ground potential throughout the system, providing the return path for all 120V loads.

This conductor’s role becomes even more critical in multi-wire branch circuits. Here, it carries only the difference in current between the two ungrounded (hot) conductors. This is known as the unbalanced load on neutral. If the loads on each hot leg are perfectly balanced, the current on the neutral can theoretically be zero. However, in practice, loads are never perfectly balanced, and the neutral must be sized to handle the maximum possible unbalanced current.

Grounded Conductor vs Grounding Conductor: A Critical Distinction

One of the most frequent points of confusion for apprentices and even some seasoned electricians is the difference between grounded conductors and grounding conductors. Misunderstanding this can lead to unsafe installations.

• Grounded Conductor (The Neutral): This is a circuit conductor that normally carries current back to the source. It is intentionally grounded and is a critical part of the circuit’s operation. It’s considered a current-carrying conductor.
• Equipment Grounding Conductor (EGC): This conductor, often called the “ground wire,” does not carry current during normal operation. Its sole purpose is safety. It connects the non-current-carrying metal parts of equipment back to the system’s grounding point. In the event of a fault where a hot wire touches a metal frame, the EGC provides a low-impedance ground-fault current path, allowing a large current to flow and quickly trip the overcurrent protection device (breaker or fuse). This is a prime example of the difference in grounding vs bonding principles.

A related term, the continuous grounding conductor, typically refers to the EGC, which must be run uninterrupted (or with proper splices) to all points in the circuit to ensure a reliable safety path.

Grounded Conductor Identification and NEC Rules

Because the grounded conductor serves a different purpose than ungrounded (hot) conductors, the NEC mandates specific identification methods. NEC Article 200 provides the primary requirements for grounded conductor identification. For conductors size 6 AWG or smaller, the insulation must be white, gray, or have three continuous white or gray stripes on insulation that is not green. For conductors larger than 6 AWG, they can be re-identified at all termination and splice points with white or gray marking that encircles the conductor.

Sizing a Grounded Conductor: Following NEC Article 250

Correct grounded conductor sizing is not just about matching the size of the hot conductors; it requires careful calculation based on NEC rules. The process of sizing grounded conductor loads is primarily found in NEC 220.61. While the general rule is that the neutral must have an ampacity to carry the maximum unbalanced load, there are specific steps for services and feeders.

Step-by-Step: Calculating Service Neutral Conductor Size

1. Calculate the Net Load: Determine the total calculated load on the ungrounded conductors according to NEC Article 220.
2. Apply Demand Factors for the Neutral Load: Per NEC 220.61, calculate the maximum unbalanced load. This is the maximum net calculated load between the neutral conductor and any one ungrounded conductor. A demand factor of 70% can be applied to the portion of the unbalanced load over 200 amperes.
3. Account for Non-Linear Loads: If a significant portion of the load consists of non-linear loads (e.g., electronic ballasts, computer power supplies), the 70% demand factor is permitted by NEC 220.61, but the calculation must account for harmonic currents that can add up on the neutral. In these cases, neutral conductor sizing may need to be equal to or even larger than the ungrounded conductors.
4. Verify Minimum Size: The service neutral conductor must not be smaller than the required grounding electrode conductor size specified in NEC Table 250.66 (as referenced by 250.102(C)(1)). Do not use NEC Table 250.122 for this; that table is for sizing the equipment grounding conductor. This is a critical step in proper ground conductor sizing.

Always consult the latest nec grounding chart or nec grounding table for specific sizing requirements like those in 250.66 NEC.

The Grounding and Bonding Connection: NEC 250 Explained

The relationship between the grounded conductor and the grounding system is defined in article 250 of the National Electrical Code. At the service disconnect (and only at the service disconnect for a non-separately derived system), the grounded conductor is bonded to the enclosure and the equipment grounding system. This connection is made via a main bonding jumper or, in some equipment, a system bonding jumper.

This bond connects the neutral bus bar to the grounding bus bar, establishing a single point of connection to the earth via the grounding electrode conductor. This single bond is critical. If neutrals and grounds are bonded elsewhere downstream, it can create objectionable current, where neutral return current can flow on the EGCs and metal piping. This violates NEC 250.6. On the line side of the service disconnect, a supply side bonding jumper may be required to bond metallic conduits or equipment.

Key Considerations for Grounded Conductors

• A grounded conductor is a current-carrying conductor by design and must be treated with the same respect as an ungrounded (hot) conductor.
• Proper grounded conductor identification (white/gray) is a mandatory safety requirement outlined in NEC Article 200.
• Never connect the grounded (neutral) conductor to the equipment grounding conductor anywhere downstream of the main service disconnect, except as permitted for a separately derived system.
• Proper grounded conductor sizing is critical for safely handling the unbalanced load on neutral and preventing overheating.
• The equipment grounding conductor (often called the continuous grounding conductor in the field) provides the essential ground-fault current path and must be installed correctly.

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Frequently Asked Questions (FAQ)

What is the difference between a grounded conductor and an equipment grounding conductor?

The primary difference is their function. A grounded conductor (neutral) is a circuit conductor that carries current during normal operation. An equipment grounding conductor (EGC) is a safety conductor that does not carry current normally; it only carries current during a ground fault to facilitate the opening of the overcurrent device.

How do you determine the correct grounded conductor sizing according to the NEC?

Grounded conductor sizing is determined based on NEC 220.61, which requires calculating the maximum unbalanced load it will carry. The size must also not be less than the required grounding electrode conductor specified in NEC Table 250.66 for service conductors. This is different from the EGC, which is sized per NEC Table 250.122.

Where in the code can I find rules for grounded conductors and grounding?

The main articles are NEC Article 200, which covers the “Use and Identification of Grounded Conductors,” and NEC Article 250, which is the comprehensive guide for all “Grounding and Bonding” requirements. Reading article 250 of the National Electrical Code in its entirety is essential for every electrician.

What is a system bonding jumper and why is it important in NEC 250?

A system bonding jumper is the conductor or screw that connects the grounded conductor (neutral) to the equipment grounding conductor and the enclosure at a service or a separately derived system. As detailed in nec 250, its purpose is to create the essential link that allows fault current to return to the source, ensuring that breakers trip during a ground fault. Without it, the ground-fault current path is incomplete.