Wiktor Wise
In electrical wiring, the term common typically refers to the common wire, which is an essential component in modern electrical systems. The common wire serves as the return path for electrical current in a circuit, completing the electrical circuit and allowing electrical devices to function properly. It is the lead that is common to all devices from the same control voltage source and is often grounded. In a two-way switch system, the common wire is critical for the correct functioning of the circuit. While the term common wire is often used interchangeably with neutral wire, especially in HVAC systems or thermostat installations, the two terms are not always synonymous.
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What You'll Learn
The common wire is the return path for electrical current in a circuit
The "common wire" is a term used to refer to the neutral wire in houses and electrical circuits. It is the return path for electrical current, completing the circuit and allowing electrical devices to function properly. In a lighting circuit, the common wire is the wire that feeds power into a light switch, while the L1 or L2 wires are the switched lives.
In a two-way switch system, where one light fixture is controlled by two switches, the common wire is essential for the circuit to function correctly. It is typically at or near ground potential, making it safer to work with than hot wires. However, if there is an issue with the electrical circuit or the breaker box malfunctions, the common wire can still carry live current, posing a risk of electrical shock.
The common wire is also known as a permanent live wire in lighting circuits and can be used in heating systems, where each component requires a permanent live connection. It is identified by its white or grey colour, as standardised by the National Electrical Code (NEC).
In a broader sense, the term "common" refers to the lead that is common to all devices from the same control voltage source. It has no contacts or switches and is often grounded, although this should not be assumed. This understanding of "common" is particularly relevant in industrial applications, where "common control" refers to a control circuit voltage that matches the line voltage.
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It is often the neutral wire
In electrical wiring, the term "common" is often used to refer to the neutral wire, which is typically marked with the label "COMMON" or abbreviated as "COM". This wire is crucial in completing an electrical circuit and ensuring the proper functioning of smart switches and other electrical devices.
The neutral wire is an essential component in modern electrical systems, particularly in homes built after 1985. It provides a return path for electrical currents, allowing them to flow back to the power source and complete the circuit. This wire is usually identified by its white colour, in contrast to the black wires that serve as the "hot" or live wires carrying electrical current to the light switch.
The role of the common or neutral wire becomes especially important when dealing with smart switches. These devices often require a constant trickle of power to remain connected to your home's Wi-Fi and maintain their smart functionality. While traditional switches break the circuit when turned off, the neutral wire ensures that a small amount of power continues to flow, keeping your smart switch operational even when it's in the off position.
It's worth noting that not all switch locations within a home may have a neutral wire. This can pose a challenge when installing smart switches, as they often require a neutral wire to function properly. In such cases, an alternative option is to set up a smart hub, although this adds an extra step and expense to the process.
To determine if your home has neutral wires, one key factor is the age of the property. Homes built or renovated after 1990 are likely to have neutral wires, while those constructed before 1980 may lack the necessary neutral wiring for smart switches. For homes built in the transitional period of the 1980s, it's advisable to physically inspect the wiring or consult an electrician to ascertain the presence of neutral wires.
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It is usually grounded
In electrical circuits, the term 'common' is used to refer to a specific part of the circuit. It is a dedicated return path for all loads, and some common circuits can have voltage at them. The common terminal is usually grounded and is often made of dark brass, copper, or black. It serves one of two purposes: either it accepts the incoming black (hot) wire from the power source, or it connects to the black (hot) wire that leads to the light fixture.
In a single pole double throw switch, the common terminal is common to both the top and bottom terminals. The "hot" wire is connected to the common terminal so that when the switch is in the up position, the terminal becomes energised, and there will be no voltage on the bottom terminal. Conversely, when the switch is in the down position, the bottom terminal becomes energised, and there will be no voltage on the top terminal.
In a three-way switch, the common terminal is the last screw and is darker than the travellers. It is always installed with a grounding screw connected directly to the metal strap of the switch. The grounding screw is used for safety and is usually a green screw attached to the metal strap of the switch. The ground wire is not intended to carry any current unless something fails. It is used to protect against electric shock and to provide an easier path for electricity to flow during electrocution.
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It is common to all devices from the same control voltage source
In electrical circuits, the term "common" typically refers to a wire or terminal that is shared between multiple devices or components. This common wire or terminal acts as a "common" connection point, allowing for the flow of electricity between different parts of the circuit.
Now, let's break down the statement, "It is common to all devices from the same control voltage source." Here, the word "common" indicates a shared aspect among multiple devices. In this context, it refers to a voltage source that is common to, or shared by, all the devices in question.
A control voltage source is a type of electrical source that provides a specific voltage to control various parameters within a system. This voltage can be used to send signals, automate processes, or adjust settings in electronic devices. For example, in electronic music production, control voltages are used to automate changes in parameters over time, allowing musicians to focus on their performance rather than manually adjusting equipment.
When it is stated that it is "common to all devices," it means that all the devices in consideration are connected to and influenced by the same control voltage source. This shared voltage source acts as a standard or reference point for the devices, providing a consistent voltage level that is used to regulate their functions.
By having a common control voltage source, the devices can be synchronized and coordinated with each other. This allows for consistent performance and behavior across the devices, ensuring they operate within the same voltage range and respond to the same voltage signals or changes. This is particularly important in applications where multiple devices need to work together seamlessly, such as in distributed energy grids or complex electronic systems.
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It is also called the COM wire
In electrical wiring, the term "common" refers to a wire that is shared between multiple devices or locations. This is often the case with light switches, where a single "common" wire can be used to control multiple lamps. This wire is usually labelled as "COM".
In a single pole, double-throw switch, the "common" terminal is connected to both the top and bottom terminals. The "hot" wire is linked to the common terminal, which becomes energised when the switch is in the upper position, causing the bottom terminal to lose voltage. Conversely, when the switch is in the down position, the bottom terminal becomes energised, resulting in the top terminal losing voltage.
In a three-way switch, there are two sets of contacts internally connected to a common pole, typically marked as "COMMON". This type of switch features normally closed (NC) and normally open (NO) contacts. Unlike in plumbing, where a normally closed valve blocks fluid flow, electrical normally closed contacts allow power to pass through.
The term "common wire" is also used in heating systems to refer to the fixed live wire in switch devices such as room stats, cylinder stats, and programmer port valves. This wire is not typically described as a "common conductor" but rather as the common contact to which the incoming live wire is connected. This could be a permanent live wire or a switched live wire from an upstream device.
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Frequently asked questions
The common wire is the lead that is common to all devices from the same control voltage source. It serves as the return path for electrical current in a circuit. It is often grounded but this should not be assumed.
Common in a heating system is the fixed live, which is sometimes but not always permanently live. It is generally connected to the incoming live.
In a two-way switch system, the common wire is critical to ensuring the circuit functions correctly. It carries current and is typically at or near ground potential, making it safer than hot wires.
In a single pole double throw, "common" refers to the terminal that is common to both the top and bottom terminals. The "hot" wire is connected to the common terminal so that when the switch is in the up position, the terminal becomes energised.
