To make the lighting in a house or apartment work, two wires need to be connected — the phase (live) and the neutral. Before installing electrical fittings and configuring their operation, it’s important to know what goes to the switch: the live or the neutral.

Let’s take a look at a standard wiring diagram. It assumes that the neutral wire goes directly to the light fixture, while the live wire passes through the switch and can be interrupted. It might seem that an electrical appliance will function normally even if the wires are swapped.

Can the standard wiring scheme be changed?

In fact, you should not swap the wires, even if it seems like the light fixture will work fine that way. Regardless of the type of switch, it must interrupt the live wire, not the neutral. Below, we’ll explain why switching the wires is definitely incorrect.

This is because the live wire always carries alternating current relative to the neutral. The neutral, in turn, always has zero potential relative to the ground. In a properly functioning power network, it acts as the grounding conductor.

So, once you understand what live and neutral mean, it becomes clear why following the standard wiring scheme is crucial. In single-phase or three-phase networks, the neutral conductor must be grounded. For example, this is the default configuration for transformers and generators.

What happens if you connect it incorrectly?

To clarify, let’s refer to the 7th edition of the Electrical Installation Rules (PUE). It states that in two- or three-wire single-phase networks with grounded neutral, single- or double-pole switches may be used, and must be installed in the live conductor circuit.

So, according to the rules, the live wire must be interrupted. Changing this setup is not just discouraged — it’s dangerous. If the switch interrupts the neutral wire instead, the socket or bulb holder will remain live even when the light is off. As a result, if you try to replace the bulb, you could get an electric shock.

Incorrect wiring leads to another issue. If the live wire is constantly connected to the socket, bulbs may flicker or blink.

Why the switch must interrupt the live wire

As mentioned earlier, this wiring scheme is standard for good reason. It has to do with some key differences between live and neutral wires, which we’ll now discuss:

  • The live wire delivers electrical energy — it is the active part of the current and powers electrical devices. When switched off, power supply stops.
  • The neutral wire returns the electrical current to the source. It is grounded and relatively safe compared to the live wire.
  • With correct wiring, the live wire is interrupted when the light is turned off.
  • The electrical system will only function efficiently if the wiring order is followed precisely. Mistakes may result in short circuits, overloads, or equipment failure.
  • For electrical safety, the neutral wire must be grounded. This ensures a safe path for current and prevents voltage buildup in case of failure. With grounding in place, people are protected from electric shock when touching equipment.

So, following the standard wiring scheme allows you to safely use your electrical network and light fixtures. Only then can you protect yourself from injury and ensure stable performance of your electrical equipment.

How to identify the live wire at the switch

This is necessary to ensure proper wiring. If you know how the live wire is labeled on the switch, you can easily connect the wires correctly and ensure stable operation of the electrical network.

Note that installing electrical fittings is not a simple task — if you lack the necessary skills and knowledge, it’s best to leave it to professionals. However, if you are confident in your abilities, here’s what to do. You can identify the live wire using a special tool or tester.

Before starting, make sure the power is turned off to avoid electric shock — remove the fuse or turn off the circuit breaker.

Check the wires by gently touching each one with the tester probe. The one carrying current is the live wire. If neither wire has voltage, you’ve probably connected to the neutral. To avoid mistakes, check the voltage multiple times.

Identifying wire colors

This system helps electricians easily find the live and neutral wires. In addition to colors, pay attention to letter markings. For example, if you’re wondering what the letter L means on a switch — it stands for live. The neutral wire is labeled N.

Live wires are usually brown, black, or grey (according to Ukrainian standard DSTU 2011). During installation, conductors with blue or light blue insulation are used for neutral wires.

When learning about wiring, many ask: is live and neutral the same as plus and minus? That’s correct — they are often referred to this way. The live wire is the plus, supplying current from the source to the device. The neutral (minus) wire returns it to the source.

In DC networks, three bus bars are used — working neutral, positive, and negative. They are color-coded: blue for neutral, brown for positive, and grey for negative. The color coding is designed to avoid confusion between current-carrying and neutral wires.

Manual detection

This method is often used in private homes to avoid mistakes. You can use a manual tester or voltage probe. First, turn off the power, then strip about 1–2 cm of insulation from the wires. Separate the wires and turn the power back on.

The electrician uses a voltage tester screwdriver to identify the live and neutral wires. If the tester lights up, it’s a live wire. For three-wire systems (with grounding), a multimeter and tester are required. The tester identifies the live and neutral wires, while the multimeter checks if one of the contacts is grounded.

How lighting works with proper wiring

Most homes and apartments use single-pole switch models. When pressed, they only interrupt one conductor. For example, imagine a chandelier hanging from the ceiling, powered by a 220V single-phase household supply.

Two wires go to the light fixture — live and neutral. The switch is installed to interrupt one of them.

Since the live wire is interrupted by the switch, there is no voltage present when it’s in the "off" position. As a result, both wires are safe to handle, allowing you to:

  • replace the bulb;
  • perform ceiling repairs;
  • remove the chandelier, etc.

However, for extra safety, it’s still recommended to turn off the breaker in the electrical panel before starting any work.

By understanding what the "L" means on a switch and strictly following proper wiring practices, you can safely use your lighting equipment. Following the correct wiring scheme is not just recommended — it’s essential for safety.