Main-Follow extension leads: automatic switching explained

A Main-Follow extension lead automatically switches selected connected devices on or off depending on the operating status of one main device. This is particularly useful when several devices are normally used together, for example a computer with a monitor and speakers or a television with associated entertainment equipment.

The technology was previously also known as Master-Slave. brennenstuhl® now uses the terms Main and Follow, while the basic function remains the same.

How does a Main-Follow extension lead work?

One device is connected to the Main socket. The extension lead monitors the power consumption of this device and uses it to control the Follow sockets. When the main device is switched on and its power consumption rises above the switching threshold, the Follow sockets are activated automatically. When the main device is switched off and its power consumption falls below the threshold, the Follow sockets are switched off again.

This means that several associated devices can be controlled automatically without having to switch each one individually.

What can I use a Main-Follow extension lead for?

A typical application is a computer workstation. The computer can be connected to the Main socket, while the monitor, speakers or other peripherals are connected to the Follow sockets. When the computer is switched on, the associated devices can receive power automatically; when the computer is switched off, the Follow sockets are switched off accordingly.

The same principle can also be useful for entertainment systems where a television or another central device is normally used together with additional equipment. The most suitable setup depends on how the individual devices behave when switched on, switched off or placed in standby.

What are Main, Follow and Permanent sockets?

The Main socket is used for the device whose power consumption controls the automatic switching function. The Follow sockets are switched automatically according to the status of the Main device. Some Main-Follow extension leads also provide Permanent sockets that remain supplied with power independently of the automatic switching function.

Permanent sockets can be useful for devices that should remain powered continuously, such as certain network equipment or other devices with ongoing functions, while equipment that is only needed together with the main device can be connected to the Follow sockets.

Can a Main-Follow extension lead help save electricity?

Main-Follow switching can help reduce unnecessary standby consumption because associated devices do not have to remain powered when the main device is no longer being used. The automatic function can be particularly practical where users would otherwise have to switch several devices off manually.

How much electricity can actually be saved depends on the connected devices and their standby consumption. Some equipment may also require continuous power for updates, recordings, network functions or other background processes, so the manufacturer's instructions should always be considered.

More information on standby consumption and switching devices off is available in Save electricity with a switched extension lead.

Which device should be connected to the Main socket?

The Main device should have a clear difference in power consumption between its active and switched-off or standby states. Desktop computers, televisions and similar mains-powered devices can therefore be suitable depending on their operating characteristics.

Battery-powered devices such as laptops are generally less suitable as Main devices because their power consumption does not necessarily reflect whether they are switched on or off. A laptop may draw power while switched off because the battery is charging, or draw relatively little mains power while operating with a charged battery. In these situations, the Main-Follow extension lead may not be able to distinguish the operating states reliably.

What is the Main-Follow switching threshold?

The switching threshold is the level of power consumption used by the extension lead to determine whether the Main device is considered active. If the consumption rises above this threshold, the Follow sockets are activated; when it falls below the threshold, they are switched off.

Depending on the model, the switching threshold may be adjusted manually or learned automatically. Digital Main-Follow models can determine and store the required threshold through a learning function, while other models use a manual adjustment control. Always follow the instructions for the individual extension lead when setting up the automatic function.

What if I do not want to use the automatic function?

Depending on the model, the Follow sockets can also be operated in a permanent mode when automatic switching is not required. This can be useful if the setup changes temporarily or if connected equipment needs power independently of the Main device.

The available operating modes depend on the individual Main-Follow extension lead, so check the product specification and operating instructions for the functions provided.

What should I consider when choosing a Main-Follow extension lead?

First consider which device will control the system and which connected devices should follow it automatically. Check whether permanent sockets are also required for equipment that needs continuous power. The number and arrangement of sockets, cable length, maximum electrical load and additional features such as surge protection or USB charging may also influence the choice.

As with every extension lead, the combined power consumption of all connected devices must remain within the maximum electrical load specified for the individual product. Automatic switching changes how the sockets are controlled, but it does not increase the electrical capacity of the extension lead.

When is a Main-Follow extension lead a good choice?

A Main-Follow extension lead is particularly useful when several devices are normally operated together and should not remain powered unnecessarily once the central device is switched off. It combines automatic control with the convenience of a multi-socket extension lead and can reduce the need to switch associated devices manually.

If the connected devices need to be controlled independently rather than automatically as a group, an individually switched extension lead may be the more suitable solution.