The phrases “line” and “load” are shorthand terminology in the electrical trades that refer to cables that transport electricity from a source to a device (line) vs those that convey power to other devices farther along the circuit (load).
The phrases line and load can be used in a variety of situations in an electrical system.
Line vs Load Wire
The words are used in the scope of a single device and electrical box, with the line wires, upstream wires, or incoming wires describing the wires that carry electricity into the box. On the other hand, load, downstream, or outgoing wires describe the wires that travel forward to other devices.
Differences between line and load wire in various applications are described below.
Service Entry and Main Panel
An electric meter’s line side receives the utility company’s incoming feed. It exits the meter on the load side and feeds a disconnect or electrical service panel on the line side.
When it comes to ground-fault circuit-interrupter (GFCI) outputs, the terms line and load have a unique significance. For connecting wires, GFCIs contain two sets of screw terminals: one designated LINE and the other marked LOAD.
When the line terminals are connected, the outlet only provides GFCI protection for that outlet. However, when the line and load terminals are connected, GFCI protection is provided for that outlet as well as additional normal outlets downstream on the same circuit.
On a single circuit, outlets, switches, and other electrical devices are often connected in multiples. The line is the wire that travels from the service panel to the device with the first device. Whereas the load is the wire that runs to the second device downstream on the circuit from the first device with the second device.
Furthermore, the line at the second device is the power source from the first device; the load is the wire that goes out to the circuit’s third device, and so on.
Identifying Line or Load Wire
The best method to distinguish between line/hot and load wires is to look at the insulation colors. Neutral wires are white and grey; ground wires are green with yellow stripes, green and copper, black can be line/upstream wire, and red or black can be load/downstream wire.
However, there are other ways to identify line and load wires as well.
Position of the Wires
Line/incoming wires are always attached from the bottom to the electrical panel, while load wires are connected from the top. You can tell the difference between line and load wires in the electrical panel by looking at the location of the attached wire on the panel box.
But if you are unable to locate the wires on the panel box, seek advice from a friend or a qualified electrician who can assist you in safely resolving the issue.
Use a Voltage Tester
A voltage stick senses voltage without contacting the bare copper wire. Use a voltage pen to test every wire linked to the switch. However, never leave exposed wires dangling in any case. If the pen tester illuminates red, that wire is line wire. On the other contrary, if the pen does not shine at all, that wire is a load wire.
When checking the current-carrying wire without unscrewing the wire’s connection to the meter box, a volt stick is a useful tool to have. But, before performing any electrical repairs or installations in your home’s main switch box, it’s best to switch off the power breaker or main switch.
Use Digital Multimeter
A multimeter is an electrical instrument that measures electric values, voltages, resistance, and current in a circuit. To identify the line and load wires in your meter or socket, set your multimeter to AC voltage and read 200 volts. The red probe is pointing to V, whereas the black probe reads COM (voltage).
Now, touch the terminals of the wires connected to the switch with the shielded terminals of the multimeter. If it displays 120 volts or higher, your meter box or controls have a line and load wires.
Use Neon Screwdrivers
A neon screwdriver is a type of screwdriver that has a neon light within the translucent plastic handle and a metallic tip that is used to touch the exposed wire or the screws that link the wire to the meter box or socket. A finger presses on the metallic cap of a neon screwdriver as it is pushed into the hole of an electric socket, bulb holder.
Additionally, when checking the current flow, ensure the power is turned on. When the hot wire is touched, the neon light illuminates, indicating that current is flowing in that wire; if the neon light does not shine, no current is flowing in that wire.
Frequently Asked Questions
Is line or load the hot wire?
The line is constantly hot. The wire that connects the switch to the gadget is known as the load. If the switch is closed, the load will be hot.
However, line and load can sometimes mean different things based on the context. For example, when constructing low-voltage circuits “line” refers to the components of the circuit that operate at full home voltage as opposed to the low-voltage wire and devices that operate after the voltage is stepped down at a transformer.