Electric motors of all types – AC single-phase or three-phase and DC – have two common characteristics during starting and run-up. Without some form of control, the motor will take very high currents, and the switching may itself cause voltage spikes.
The high currents risk overloading the supply and the overvoltages can damage the electrical insulation of the supply or the motor itself. Before the advent of power electronics these over-currents and over-voltages were usually controlled by the temporary introduction of resistors into the motor supply, and sometimes (for three-phase motors) also reduced-voltage switching using a star-delta starter.
However, when spares or replacements are wanted for existing installations and motors of all types (such as DC motors, slip-ring motors, speed-controlled motors or closed transition star-delta starters) engineers are always able to design and manufacture suitable resistors. Our expertise in application engineering means that we can offer you a complete range of dedicated resistors for starting, braking and speed control that meet European, international and bespoke specifications.
