When designing electrical projects, depending on the criticality of the installation and its operation, it is essential to consider the use of fixed or withdrawable devices in electrical panels.
But what exactly are fixed and withdrawable devices?
A fixed device, whether modular, moulded case (compact), or air circuit breaker (open), is a piece of equipment that must have its connections disconnected in order to be replaced.
On the other hand, withdrawable devices are designed so that they can be replaced without the need to disconnect existing connections. This is their major advantage — the replacement of withdrawable devices causes minimal disruption to operations and energy supply, whether to the affected circuit or the entire electrical panel. In fact, it is possible to replace a device without having to switch off the panel.
Withdrawable devices are made up of assemblies consisting of a fixed part (base or chassis) and a movable part (switching or protection device), and they can be of two types:
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Base-mounted withdrawable
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Chassis-mounted withdrawable
In base-mounted types, we find modular and moulded case (compact) devices, as shown in the images below.
In chassis-mounted withdrawable devices, we again find moulded case circuit breakers and air circuit breakers, as shown in the images below.
However, in order to benefit from the ease of replacing a faulty device with a new one, it’s important to keep in mind that equivalent devices must be kept in stock, fully equipped with the necessary accessories. This ensures the replacement can be carried out quickly and efficiently.
In summary, the use of fixed devices requires shutting down the electrical panel for replacement — with all the associated inconveniences and potential losses — whereas withdrawable devices simplify both the replacement process and overall intervention.
P.S. If the withdrawable devices are equipped with auxiliary components (e.g. signalling contacts, coils, etc.), don’t forget to acquire the appropriate interconnection accessories to link the fixed and movable parts of the device.