3-2 BE1-50/51B-235/-236
Functional Description
9252000898 Rev —
Power-off sensing circuits measure the voltage across a capacitor at power-down and power-up. These
circuits determine how long power has been removed based on the difference voltage and the circuit’s
RC time constant. This provides information from the integrating reset function even when power has
been entirely removed.
The microprocessor performs the program operations based on the inputs and the internal software
program. When the sensed current exceeds the TIME PICKUP setting, the ACTIVE/PICKUP LED turns
from green to red. The 50-A/51 contact is closed in accordance with the TIME characteristic equation or if
the sensed current exceeds the INST PICKUP setting. Likewise, sensed current exceeding the
Instantaneous Overcurrent B Pickup selector switch setting causes the 50-B Trip output contacts to close.
Outputs
Each protective element (time overcurrent (51), instantaneous overcurrent A (50-A), and instantaneous
overcurrent B (50-B)) is equipped with a set of normally-open contacts rated for tripping duty. A system
circuit breaker controlled by the 51 or 50-A output contacts can be manually tripped by connecting a
jumper across the Time Overcurrent Manual Trip jacks or the Instantaneous Overcurrent Manual Trip
jacks. (Manual trip jacks are not provided for the system circuit breaker controlled by the 50-B output
contacts.) Current flow in a trip circuit is indicated by operation of the corresponding target. The targets
will not operate without adequate relay operating power.
Target Indicators
Gravity-latched, manually-reset, current-operated target indicators are provided for the time overcurrent
(51) trip output and the instantaneous overcurrent A (50-A) trip output. A target indicator is not provided
for the 50-B trip output. The level of trip circuit current required to operate each target is individually
controlled by a circuit board jumper. The minimum operating current range can be set for 80 to 200
milliamperes or 0.9 to 2.25 amperes. See Section 2,
Controls and Indicators
for jumper locations and
function assignments.
CAUTION
Trip circuit voltage is present at the front panel trip jacks. When shorting the trip
jacks, use insulated jumpers to avoid contact with these voltages.
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