Electrical Connection Instructions
CAUTION!! Damage to the Sentronic module will result if
the “M” terminal of the Sentronic is connected to ground or
directly to line voltage!
When changing components or making any kind of
electrical alterations to any installation, existing or new, all
ground connections must be specifically checked to make
sure they are secure. If there is any doubt about
component or system grounding, the local electrical
inspector should be consulted.
The electrical connection diagrams included in this bulletin
are intended to represent the most common Sentronic
application control circuits. The system manufacturer
should be consulted when more complex circuits are
encountered.
Standard Control Circuits
Both Diagrams 3A (new Sentronic) and 3B (previous
Sentronic) show typical wiring connections and the
similarity of Sentronic and Sentronic oil pressure switches
used on three-phase motor compressors.
Sentronics are energized when they are connected to a
voltage source. In both diagrams 3A and 3B, if the
compressor controlling and overload devices are closed,
the compressor starts and at the same time, a circuit is
made from one side of the power two incoming lines to the
“L” terminal. The “L” terminal is one side of the “L”-“M”, N.C.
contact of the Sentronic module. The "M" side of the N.C.
contact is usually connected to the compressor contactor
coil. The circuit for the electronic module power is
completed by the connection of the 230/ 240 (or 115/120)
volt terminal to the other side of the incoming power line.
The electronic two-minute timing circuit operates
whenever voltage is applied to a Sentronic, and it has not
tripped. The timing will be interrupted when oil pressure
rises above 12-14 PSID and closes the Sentronic sensor.
Should oil pressure not build up sufficiently for 120
seconds, the electronic delay will time out, open its L-M
contact, break the control circuit, and de-energize the
compressor contactor to stop compressor operation.
While the compressor is running, if the compressor net oil
pressure falls below the cut-out setting of the sensor while
operating and does not re-establish sufficient pressure
within an acceptable time, the time delay circuit will open
the L-M contacts, stopping compressor operation. Once
the oil pressure switch has tripped, it must be manually
reset to restore the system to operation.
IMPORTANT: If a power interruption occurs after an oil
pressure safety trip, wait two minutes before resetting after
power is restored.
Control With Alarm
Diagrams 4A (new Sentronic) and 4B (previous Sentronic)
use an added alarm circuit. To contrast the 4 and 5 terminal
Sentronics with the new Sentronic. The new Sentronic
does not require an extra relay or auxiliary contact for an
alarm circuit.
The Current Sensing Relay Used With Compressor
Inherent Motor Protectors:
Compressors equipped with internal inherent protection
and oil pressure safety controls, will trip the oil pressure
safety control if the internal inherent protector should open
due to motor overheating or a temporary motor overload.
After an overload trip of a compressor with an inherent
protector the control circuit will still be closed, and the
Sentronic energized, although the compressor motor is not
operating. The two-minute timing circuit will activate due to
a lack of oil pressure, and after the 120 second time delay,
the oil pressure safety switch will trip. Even though the
compressor motor cools sufficiently for the internal
inherent protector to automatically reset, the compressor
cannot start until the oil pressure safety control is manually
reset.
This is normally not a problem, since the compressor, if
properly applied, will seldom if ever trip on the internal
inherent protector. If it should happen to do so, the fact that
a protector trip has occurred, indicates that the system
operation should be reviewed. However, on frozen food or
other critical applications where a product loss may occur,
if a compressor shutdown should occur during the night, or
over the weekend when the equipment in unattended, it
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