The disconnection equipments are medium / high power electromechanical devices, which are inserted into the main electrical circuit of the rolling stock, with variable allocation depending on the purpose of the object.

In this context, the following product categories can be defined: disconnectors, change-over and earthing switches.

But let’s get to know them in more detail!


As the name implies, the Disconnectors “disconnect” the power line, opening the circuit and preventing the passage of current. This operation is necessary when you want to isolate the devices downstream of them from the power supply, for example to perform maintenance operations, in order to ensure maximum safety for operators.

Depending on the rolling stock and the application, we can find them on the roof or under the body of the train and they can be moved manually, through suitably insulated levers, or by electromechanical or pneumatic actuators.

Change-over switches

These devices expand the operation of the disconnectors, as they are not limited only to opening or closing a circuit, but distribute the electrical power on different branches, according to the devices to be powered. They therefore have several inputs and / or outputs, connected to each other through movable blades which, as for the disconnectors, can be operated manually by means of a lever or by an electromechanical or pneumatic actuator.

As an example, considering the image below, we could have the following states:

  • Service: connects the main power supply (e.g. pantograph or third rail) to the motors of the rolling stock and all other auxiliary services;
  • Auxiliaries: isolates the motor line and connects the main power supply to the auxiliary services only;
  • OFF: totally disconnects the rolling stock from the main power supply, in fact it is equivalent to a disconnector;
  • Workshop: connects the power supply of the workshop, carried out through a special socket, to the auxiliary services for maintenance operations only.

Earthing Switches

The Earthing Switches are necessary to ground the electrical circuit of the rolling stock during maintenance operations, in order to guarantee the full safety of the operators.

During operation, the input poles are short-circuited directly on the grounding circuit. We can find them in different configurations, stand-alone or even combined with change-over switches, depending on the needs and, as for the devices described above, also in this case they can be moved manually or with the aid of electromechanical or pneumatic actuators. .

It is therefore necessary, during their design, to carefully consider the following aspects:

  • minimum insulation distances between components, based on the operating voltage, to prevent current leakage and / or the formation of electric arcs that would affect the safety of operators, as well as the integrity of the device itself;
  • high performance of the electrical contacts, to withstand the thermal and electrodynamic forces due to the high current intensity and avoid the formation of electric arcs that can compromise the integrity of the device;
  • clear and unambiguous identification of its status, through indicators, indelible status plates, etc.
  • implementation, depending on the needs, of mechanical or electromechanical interlocks (such as electromagnets, keys, doors, etc.) to prevent the device from being moved erroneously with consequent risks for its integrity and for the safety of the operators.

Based on these important aspects, we at SPII design customized products to meet customer needs, combining modular solutions with ad hoc parts.

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See you next time,
Giuseppe Musotto