What Does the Neutral Wire Do?
If you’re confused about the white wire and what its purpose is, you’re not alone
Highlights
The neutral wire is the white wire that accompanies the black wire in a neutral circuit.
Its job is to return unused electricity back to the panel.
Smart switches require neutral wires because they’re always on.
Call a pro if a home’s electrical system doesn’t include neutral wires.
Most electrical wiring projects are essentially color-coded. Basic wiring projects can seem simple to figure out with the directions or diagram on the back of a device, whether it’s a switch, outlet, or plug. But there is danger lurking in those wires, and knowing what each of those wires does—specifically the neutral—is essential to ensure that anyone attempting a wiring job is safe and the device is wired properly. So what does the neutral wire do? This guide will explain.
What Is the Neutral Wire?
The neutral wire is typically the white wire accompanying the black wire in an electrical circuit. Its purpose is to act as the path for unused electricity back to the electrical circuit. It’s typically attached to the white (or silver) screw on the back of an outlet or another device, while the black wire (or hot wire) connects to the gold screw. The ground wire is typically attached to the green screw.
This wire travels from the panel to the device and then back to the panel. It can be connected to other neutral wires in junction boxes but never has a switch or device connected to it.
What Does the Neutral Wire Do?
Essentially, a neutral wire completes the flow of the electrical circuit. This is a necessary function that allows the electrical system to work safely and correctly.
Electrical circuits are called circuits because they’re essentially large loops. Electricity flows through the panel, through a circuit breaker, and out to the devices through the hot wire, typically black in residential wiring. The electricity then reaches the device, where a portion is used to power it. The unused electricity must then return back to the panel through the neutral wire, which connects to the neutral bus bar—a grounded bar in the electrical panel.
This setup allows electricity to flow through each circuit continuously and back to the panel safely. Without a neutral wire, the electricity that flows to the device can’t return, and this can cause overheating and other dangerous scenarios.
Direct Current vs. Alternating Current
Direct current (DC), such as the electricity provided by the battery in a car, does not use a neutral wire. Instead, these circuits use a positive wire and a negative wire. This facilitates the electricity’s flow, which is a continuous, one-direction loop.
Alternating current, like the electricity used to power homes and buildings, is different. Alternating current is constantly switching between the positive flow of charge and the negative flow of charge, changing direction every so often. A neutral wire helps facilitate the flow of current in this situation.
That’s a very high-level explanation, but the important point to understand is that DC power does not require a neutral wire while AC power does.
The “Neutral” Misnomer
The term “neutral” brings to mind thoughts of harmlessness or innocuousness, but that’s not really the truth. In a live circuit, a neutral wire is always carrying electrical current unless a switch controls it. This means that if someone were to touch or ground out the neutral wire, they stand a good chance of being shocked with a substantial amount of voltage.
According to the National Electrical Code, the neutral wire is the “grounded conductor.” It’s called this because the neutral is grounded through its connection to the neutral bus bar. However, it is not the grounding conductor, which is the green wire that grounds the electrical devices to an electrode driven into the ground. The grounding wire does not carry electricity under normal circumstances but does give excess or dangerous electricity an escape route that prevents harm to people and devices.
It’s important to understand these distinctions.
Smart Switches and Neutral Wires
Some homes don’t have neutral wires—particularly homes built and wired before the 1960s. Many homeowners discover this when attempting to install a smart switch, as these devices require a neutral wire to function.
Why do they need a neutral wire? It’s simple, really.
A typical switch operates by mechanically interrupting the hot wire, stopping the flow at the switch. Smart switches do this electronically. Think of the switch’s internals as a brain that connects it to the Wi-Fi. This brain needs power, so it must always be on a constantly live loop, with a hot lead and neutral wire running to and from the device to keep the electronics in the switch operating.
With the switch constantly powered, it can receive signals via Wi-Fi. It can then connect or disconnect the load running to the wire, controlling the device electronically.
Frequently Asked Questions
Confusingly, not all circuits have neutral wires. Circuits carrying 208-volt power to certain devices (not usually residential, but still worth noting) have three hot leads and one ground, but no neutral. Also, 240-volt circuits don’t have white neutral wires, using gray wires for neutrals instead.
But homes that do not have neutral wires on their 110- or 120-volt circuits will need them installed during renovations or upgrades. For this process, it’s best to call a local electrician to handle the job. These pros know how to safely upgrade home wiring and electrical services to ensure that the proper, code-approved devices and wiring are in place.
When the neutral wire is not connected, power cannot flow safely back to the electrical circuit as it should. The excess electricity may travel through different paths to escape instead, which could then cause a voltage influx that could harm electrical equipment or even present a shock hazard.
The ground wire is a safety wire not intended to carry current in normal situations. While these two wires can be connected at the main panel, connecting them beyond that point, including in a subpanel, could cause numerous problems. It will create multiple return paths for excess electricity. It may prevent the neutral breaker from tripping after a fault since they will share the load with the ground wire. The wires in the subpanel will be left holding current, which could present a shock hazard.
A broken or poorly connected neutral wire will cause unequal voltage, meaning some appliances will have higher than average electricity flowing into them while others will have less power than usual. This uneven electrical distribution could result in lights flickering or some outlets sparking when plugs are inserted. If you suspect you have a loose neutral wire, call alocal electrician as soon as possible.