Otis Singleton
In electrical systems, per line refers to the electrical wires that deliver power from the source to a device. These are called line wires or supply lines and are always hot, meaning they carry an electrical current. The line is the incoming electricity, and the load is the outgoing electricity. Line wires are generally black and are usually found lower than load wires as they are delivering power.
| Characteristics | Values |
|---|---|
| Definition | "Line" refers to the electrical wires that deliver power from the source to a device. "Load" refers to the wires that carry power onwards to other devices further along the circuit. |
| Wiring | Line wires are usually black and are always "hot", meaning they carry an electrical current. Load wires are usually white, but can also be red or blue. |
| Applications | The terms "line" and "load" have applications at different locations in an electrical system, including the electric meter, electrical service panel, and outlets and switches. |
| Circuit Breakers | In the context of circuit breakers, "line" refers to the parts of the circuit that are at full household voltage, while "load" refers to the electrical demand or power draw that a device or appliance places on a circuit. |
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What You'll Learn
Line and load wires
Load wires, on the other hand, take power from the line wire and deliver it to outlets, switches, and fixtures. They carry electricity from the device or system back to the power source. Load wires are only live when they are connected to an active outlet, switch, or device. These wires are usually marked with white insulation but can also be red or black.
It is crucial to distinguish between line and load wires to ensure the electrical system is wired correctly and safely. Mixing up these wires can result in a short circuit, damage to the electrical system, or even a fire. When installing GFCI outlets, for example, it is essential for safety and protection to understand which wires are line and which are load. GFCI outlets have distinct "Line" and "Load" screw terminals for connecting wires.
To identify line and load wires, you can use a multimeter or a non-contact voltage tester. A multimeter measures electrical voltage, current, and resistance. By touching the probes of a multimeter to the black and red wires, you can determine which is the line wire and which is the load wire based on the voltage reading. A non-contact voltage tester, on the other hand, allows you to detect whether a wire is live without physically touching it.
When working with line and load wires, always turn off the power to prevent accidents or injuries. Label the wires to avoid confusion, and use wire nuts to connect them securely. If you are not comfortable working with electrical wires or are unsure about the wiring in your home, it is best to seek professional help.
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Line and load connections
The electrical terms "line" and "load" refer to wires that deliver and carry power. In the electrical trades, the terms "line" and "load" are shorthand words that refer to the electrical wires that deliver power from the source to a device (line), and carry power onwards to other devices further along the circuit (load).
The incoming feed from the utility company comes into the line side of an electric meter. It leaves the meter from the load side and then feeds the line side of a disconnect or electrical service panel. The service panel also has line and load connections—the line feeds the main breaker in the panel, while the individual branch circuit breakers can be considered the load, with respect to the main breaker. Line wires are usually found lower than load wires, as the line wires are delivering power. Load wires tend to be positioned near the top of outlets and switches. Line wires are usually black, and load wires are usually white. However, this is not always the case, and you should consider multiple factors when identifying which wire is which.
Outlets (receptacles), switches, light fixtures, and other electrical devices are typically wired in multiples on a single circuit. With the first device, the line is the wire running from the service panel to the device, and the load is the wire running from the first device to the second device downstream on the circuit. At the second device, the line is the power source coming in from the first device; the load is the wire going out to the third device on the circuit, and so on. The same meaning can apply to the device itself. The line side of an outlet is where you connect the incoming source power. The load side is where the power leaves the device (or electrical box) and travels down the circuit.
When wiring low-voltage circuits, such as those supplying doorbells or landscape lights, "line" refers to the parts of the circuit that are at full household voltage (usually 120 volts), to distinguish them from the low-voltage wiring and devices that are used after the voltage is stepped down at a transformer. "Load" is also a general term to describe the electrical demand, or power draw, that a device or appliance places on a circuit. For example, on a lighting circuit, you can add up the maximum wattage of all of the light fixtures on the circuit to calculate the "total load," or maximum potential power demand of all the lights.
Connecting to the line terminals only results in the outlet providing GFCI protection only for that outlet. Connecting for the line and the load terminals (using two electrical cables or two sets of pigtail wires) provides GFCI protection for that outlet as well as for other standard outlets located downstream on the same circuit.
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Line and load in low-voltage circuits
In electrical wiring, the terms "line" and "load" are shorthand words that refer to the electrical wires that deliver power from the source to a device (line) and those that carry power onwards to other devices further along the circuit (load). These terms are relative to the location of the device in the circuit, as the load wire for one outlet becomes the line wire for the next outlet downstream.
When wiring low-voltage circuits, such as those supplying doorbells or landscape lights, the "line" refers to the parts of the circuit that are at full household voltage (usually
The "load" is also a general term to describe the electrical demand or power draw that a device or appliance places on a circuit. For example, on a lighting circuit, you can calculate the "total load" or maximum potential power demand by adding up the maximum wattage of all the light fixtures on the circuit.
In the context of a single device and electrical box, the wires that deliver power into the box are described as the line wires, also known as upstream wires or incoming wires. Conversely, the wires passing onwards to other devices are described as load, downstream, or outgoing wires. Line wires are usually found lower than load wires as they are delivering power, and they are usually black, while load wires are usually white. However, this is not always the case, and one should consider multiple factors when identifying which wire is which.
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Line wire colour-coding
In electrical wiring, the terms "line" and "load" are used as shorthand to refer to the electrical wires that deliver power from the source to a device (line) and those that carry power onwards to other devices further along the circuit (load). Line wires are usually delivering power and are found lower than load wires in an electrical system.
Electrical wire colour-coding is a standardised system of colour markings used on electrical wiring to indicate the purpose and voltage of specific wires within an installation. These colour codes are essential for safe electrical installations and maintenance, helping electricians and technicians identify which wires are hot, neutral, or ground. This colour-coding system prevents the risk of electric shock, electrical fires, and other hazardous incidents, especially during installation, maintenance, or repair.
The specific colours used for electrical wire colour-coding can vary depending on the country and local regulations. Here are some common colour-coding standards used in different parts of the world:
North America (United States and Canada)
The National Electrical Code (NEC) in the United States and the Canadian Electric Code (CEC) in Canada govern the standards for electrical wiring installations. Here are some common colour codes used in these countries:
- Protective ground: Green, green with a yellow stripe, or bare wire
- Neutral: White or grey
- Hot (live or active) single-phase wires: Black and red (for a second active wire)
- Three-phase lines: Red, black, and blue
Europe
Most European countries, including the United Kingdom, follow the International Electrotechnical Commission (IEC) wiring colour codes for AC branch circuits. Here are the common colour codes used in Europe:
- Protective ground wire: Green with a yellow stripe (also known as the earth or grounding wire)
- Neutral: White or grey
- Hot (active) wires: Black for the first hot wire and red for the second hot wire
Solar Power and Battery Systems (DC Power)
Solar power and battery systems often use DC (direct current) power instead of AC (alternating current). The colour codes for DC power cables may follow the AC standards in some cases, but there can also be variations.
It is important to note that older installations may use different colour codes, and local customs or practices can also influence the choice of wire colours. Therefore, it is always essential to refer to the specific standards and regulations in your location when working with electrical wiring.
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Line and load in light switches
In electrical wiring, the terms "line" and "load" are used to refer to the electrical wires that deliver power from the source to a device (line) and those that carry power onwards to other devices further along the circuit (load). In other words, the line wire is the wire that provides the voltage of power to your switch from the power company, while the load wire is the wire that connects your switch to the lightbulb or another "load", such as a fan or other appliance.
When wiring low-voltage circuits, such as those supplying doorbells or landscape lights, the "line" refers to the parts of the circuit that are at full household voltage. The "load" in this context can refer to the electrical demand or power draw that a device or appliance places on a circuit. For example, on a lighting circuit, you can calculate the "total load" by adding up the maximum wattage of all the light fixtures on the circuit.
In a 3-way configuration, the "line" wire should be connected to the "common" terminal, while the "load" wire should be connected to the "C" terminal. The line wire is usually a black wire, but it can also be red or green. The load wire is usually black as well, but it can also be red. It is important to note that the colours of the wires are not always indicative of their function, so it is crucial to consider multiple factors when identifying the line and load wires.
When replacing an old switch with a dimmer switch, for example, it is important to correctly identify the line and load wires to ensure the proper functioning of the light switch. By understanding the difference between the line and load wires, you can safely and effectively install and maintain electrical devices, such as light switches, in your home.
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Frequently asked questions
"Per line" in electrical refers to the wires that carry electricity from the source to a device or appliance. These are also called "line wires" or "supply lines".
Line wires supply electricity to devices and appliances. They are always "hot", meaning they carry an electrical current.
Line wires are usually black, but this is not always the case. A volt pen can be used to determine if a wire is live, which indicates that it is a line wire.
A load wire carries electricity from a terminal point to the point of use, or from one device to the next in a series.
Line wires typically run from the breakers to the designated electrical boxes in a home. They are usually behind the walls but may be surface-mounted in unfinished spaces like attics and garages.
