causes the line through diode CR9 to rise and operate the
on transistor Q19, turns on transistor Q22, and energizes
the shunt trip relay K1 through connector J1 pin 5.
shunt trip relay driver.
2). During parallel operation (described in paragraph 3-
The shunt trip relay driver consists of transistors Q17,
4b), transistor Q19 turning on also forward-biases the
Q19 and Q22 and photocoupler U10. When transistor
Q13 in the sensor delay circuit, transistor Q8 in the low
light-emitting diode in the photocoupler. Light from the
voltage fault sensor, or transistor Q14 in the high voltage
light-emitting diode turns on the light-sensitive transistor.
fault sensor is turned on, transistor Q17 is held off and the
(The photocoupler is not used during non-parallel
shunt trip relay driver is inhibited. After the sensor delay
operation). When the transistor of U10 turns on, it
has timed out, turning off transistor Q13, either transistor
provides base drive to Q22 of the other parallel unit and
Q8 or transistor Q14 turning off allows the base of
trips the shunt trip, i.e., is parallel operation, the sensors
transistor Q17 to rise. This turns on transistor Q17, turns
in one unit trips both shunt trip breakers through the