Fortress resistors make it possible to start and stop extremely powerful electric motors - such as those on cranes, compressors, and pumps - with safety and precision.

The resistor functions to control the torque and/or speed of an electrical motor or limit the initial current inrush to an acceptable level. This is accomplished through the use of manual or magnetic controls, or with solid-state controls.

In harsh environments, such as foundries and steel mills, motors and resistors must be able to withstand "plugging" - a type of motor braking provided by reversing the voltage polarity or phase sequence so that the motor develops a counter-torque and brakes the load.

They must also withstand dynamic braking, fast acceleration of heavy loads, large amounts of dust and dirt, and occasional operator abuse. In these instances, Fortress' stainless steel stamped grid resistors offer excellent service and cost efficiency.

The most popular uses of Fortress resistors are control of AC wound rotor induction motors (slip ring motors), DC series wound motors, and AC squirrel cage induction motors. FSP resistors are also commonly used for wye-delta closed-transition starting applications.

AC Wound Rotor Induction Motor

(Slip Ring Motor)

The resistor is wired into the motor secondary slip rings, where it dissipates torque energy in the form of heat. It also provides "soft starting" as resistance is removed in steps.