64Instruction Booklet IB 33-790-1JEffective November 2010Instructions for Low Voltage PowerCircuit Breakers Types DS and DSLEaToN CorPoraTIoN www.eaton.comFig. 67 Undervoltage Trip Device.8.7.1 Undervoltage Trip AttachmentThe undervoltage trip shown in Figure 67 is an electro-mechanical device that trips the circuit breaker when thevoltage on its coil falls to between 30 and 60 percent ofnormal. The standard unit trips instantaneously. A similardevice is also available with non-adjustable time delayintended to ride through momentary fluctuations of sys-tem voltage.In operation, a moving core is normally held magneticallyagainst a stationary core and a spring. This is linked to alatch carrying a roller which restrains the main trippinglever of this assembly.When the coil voltage is reduced sufficiently, the torsionspring overcomes the magnetic attraction between thetwo cores. The moving core travels upward, and rotatesthe latch in a counterclockwise direction so that the rollermoves from beneath the tail of the main tripping lever. Atorsion spring (not visible in Figure 67) around the pivotpin of the tripping lever then rotates it in a counterclock-wise direction, causing a projection on the right side ofthis lever to strike a pin in the breaker mechanism tripshaft, and rotate the latter in a clockwise direction to tripthe breaker.Fig. 68 Undervoltage Trip Device Operation.As the breaker opens, a pin on the left pole unit shaftstrikes a vertical leg (Reset arm) of the undervoltage trip-ping lever and rotates it counterclockwise against its tor-sion spring. Another arm on the tripping lever resets theroller latch and the moving core. A slight amount of over-travel on the trip latch insures positive resetting under allconditions. Set Figure 68 for the relationship of the und-ervoltage trip device, pole shaft and trip shaft.Always connect the undervoltage coil on the line side ofthe breaker unless the attachment is equipped with atime delay device. In this case, the time delay will delaytripping of the breaker long enough to permit energizationof the undervoltage coil from the load side. Do not use anauxiliary switch contact in this circuit.8.7.2 Overcurrent Trip SwitchThis device is available as an optional accessory oneither manually operated or power-operated breakers ofall ratings. Its function is to provide a signal to indicatethat the breaker has tripped open by action of the Amp-tector trip unit due to phase or ground overcurrent. Nor-mal tripping by the trip plate, shunt trip device,undervoltage trip device, etc. does not cause it to oper-ate. It is mounted on and operates from the trip actuatorof the breaker.
