Contactor DC – C310

Questions & Answers

• What is a contactor?

  A contactor is defined according to IEV ref 441-14-33 as a mechanical switching device with only one rest position, operated other than by hand, capable of switching on, conducting and breaking currents under normal circuit conditions including operational overload.

  In common parlance, this usually refers to an electromechanical contactor where the operation of switching on and off is done by means of an electrically driven coil. Simply put, the contactor is essentially a switch for electrical power in the same way that a relay is a switch for electrical signals or small loads.

  With electrification and higher voltages in systems, contactors capable of extinguishing the resulting arc are required to safely interrupt the current, even under load in an emergency. It is therefore important to have the right contactor for the purpose. Factors to consider when choosing a contactor are current, voltage, current direction, inductance, short-circuit current, etc. This is to ensure that the current is actually broken and does not lead to more catastrophic events such as fire or similar, read more about risks here. Please contact us for help in choosing a contactor for your system.

  See our range of contactors and contacts here

  

   

• Why contactors from Schaltbau?

  A contactor is a vital safety component in any electrical system, Schaltbau stands for new patented technology. By far the longest life cycle, resulting in a low price. The patented open arc chamber technology will be larger in volume. Achieving the highest level of safety requires longevity, technical innovation and documented approval.

   

• What does ‘fail to safe’ mean?

  When an electromechanical component such as a contactor is exposed to a situation that causes it to fail, it does so safely. A contactor that has arc extinguishing in air will be able to break the current without damaging other components. In gas-filled and contactors with closed arcing chambers, there is a risk of large pressure differences occurring due to. heating, this can lead to explosions with uncontrolled consequences, e.g. current conductors can risk damaging surrounding components.

• What can make a contactor weld together?

  High short-circuit currents and an unregulated closing with load is the most common reason for the contactor to weld. This is usually due to an insufficient pre-charge. Read more about Pre-charge here.

  Excessive and high short-circuit currents can cause the contact bridge to lift and open due to the magnetic field generated by the current, called levitation. This can cause the contactor to weld because when the contactor bridge opens, micro arcing and extensive heating occur.

  Breaking higher loads than the contactor is designed for, especially high inductance can cause the contactor bridge to weld.

  Using silver oxide on the contactor pills increases the resistance to welding.

  Read more about our contactors here.

• What are bi- and monostable contactors?

  The contactor can either be controlled to one mode or both modes, for switching on or off. For example, a monostable controls the switch-on by coil, while the switch-off is controlled by a spring if the coil voltage is broken. A bistable controls both striking and breaking with the coil. A bistable contactor uses no energy to keep the contactor in the respective position.

  Read more about our contactors here.

• What happens if you overload a contactor in the short term, short circuit load?

  For each contactor, there is a short-circuit current and a time that it must withstand. If this is higher and longer than the specification, there is a risk that the contactor will weld together. What happens is that the magnetic field in the contact bridge forces the contact bridge apart and small arcs can form with the subsequent risk of the contactor welding the contact bridge. Alternatively, the heat in the contact points can be so high that they melt together.

• Why are contactors used?

  Historically, contactors have been used to directly switch on and off electrical loads, such as electric motors, and even today they are used this way in many applications. In modern systems, however, starting and stopping is often done electronically and the purpose of the contactor is mainly to enable galvanic separation and to act as a switch in the event of an abnormality or fault in the system.