Neutral and ground wires are often confused outside of the electrical trade since both conductors have zero voltage, allowing mistakes to be easily made without implementing wiring color codes. In fact, if you connect the ground wire as neutral by mistake, most devices will work correctly. However, such a connection goes against the code, as each conductor has a different function in an electrical installation.
The National Electrical Code (NFPA 70 NEC) establishes insulation colors for neutral and ground wires. Standard colors simplify electrical installation, making it safer .
- Neutral yarn colors: White or gray
- Ground wire colors: Green, yellow-green or bare
These insulation colors are only permitted for neutral and ground conductors, and using them for any of the live voltage phases is against code. Electricians work under the assumption that wiring in these colors is at zero voltage, and using white or green insulation for a live conductor would be a death trap (and against code in the first place).
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Role of neutral conductor in electrical circuits
To visualize how the neutral conductor works, consider that electrical energy is supplied as current through a voltage difference. Voltage is carried by the live conductor, but a neutral conductor is also required for two important functions:
- Serving as a zero voltage reference point.
- Completing the circuit by providing a return path for the current supplied by the energized conductor.
If only the live conductor is connected to an electrical device, it will not activate because current cannot flow regardless of the voltage applied. This is similar to how a hydroelectric turbine requires an outlet to produce movement: if the turbine discharge is blocked, water cannot flow and the turbine cannot rotate.
When an installation uses three-phase power there may be cases where the neutral conductor is not necessary.
- A three-phase system with 120V line voltage provides 208V between phases , and you can connect a 208V load between two phases without using a neutral wire. Both energized conductors carry voltage, but current can flow because they have different voltages.
- Three-phase loads, such as electric motors, are often designed to run with three live conductors and no neutral conductors . The same principle applies here: current can flow between conductors energized at different voltages.
Even though some loads do not use the neutral conductor in a three-phase installation, it is necessary for single-phase loads that use only one of the line voltages. In theory, when identical charges are connected to the three phases, their currents cancel each other and the neutral conductor carries zero current. However, this is unfeasible in real installations, and the neutral conductor carries the current imbalance between the three phases.
Role of grounding conductor in electrical circuits
The grounding conductor has zero voltage just like the neutral conductor, but it performs a different function. As its name suggests, this conductor provides a grounded connection for all appliances and equipment.
- Under normal conditions, all current returns through the neutral conductor, and the grounding conductor has no current .
- When a line fault occurs, the grounding conductor provides a return path for the fault current. Electrical protective devices can detect this condition and immediately disconnect the circuit from the power source.
Without a ground connection, appliances and equipment become energized if a live wire accidentally touches them. The fault is not disconnected, as the protection devices can only respond when there is fault current in a ground wire. In this case, whoever touches the energized surface will suffer an electric shock.
Because a ground fault can affect any circuit, the grounding conductor is necessary even when there is no neutral wire. For example, if a motor uses three live conductors and no neutral, grounding is still necessary because any one of the live wires can cause a fault.
Correctly sizing neutral and grounding conductors
Live conductors are sized for the current they must carry, and the same applies to neutral conductors in single-phase circuits (they carry the same current as the live wire). However, different rules apply for three-phase circuits: a common practice is to use the same wire size as the phase conductors, but some applications require a larger wire size for the neutral conductor.
- Grounding conductors for branch circuits are sized based on the capacity of the overcurrent protective device using tables provided in the NEC.
- On the other hand, the main service entrance grounding conductors are sized based on the capacity of the service conductors. The NEC provides tables for both cases.
By working with qualified electrical engineers from the beginning of the project, you can be assured that all components are specified in accordance with NEC and local codes. This not only provides security, but also quick approval of the project with local authorities. Electrical engineers can also suggest energy efficiency measures to save on energy bills.
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