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CHAPTER 2: INSTALLATION
239 MOTOR PROTECTION RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
39 and 44. Momentarily shorting these terminals together will cause the thermal
memory of the 239 to discharge to 0% used. The emergency restart terminals can be
used to override a trip lockout caused by a running overload or locked rotor start.
This option should be used only when an immediate restart after a lock-out trip is
required for process continuity. Discharging the thermal memory of the 239 gives the
relay an unrealistic value for the thermal capacity remaining in the motor and it is
possible to thermally damage the motor by restarting it. Shorting the Emergency
Restart terminals together will have no effect unless the motor is stopped (no phase or
ground current present). Having these terminals permanently shorted together will
cause the memory to be cleared whenever the motor stops. This will allow for an
immediate restart after an overload trip. Caution is recommended in the use of
Emergency Restart input since the thermal protective functions of the 239 will be
over-ridden and it is possible to damage the motor.
•
EXTERNAL RESET (40/45): An external reset switch which has the same effect as the
front panel RESET key or a serial port reset command can be connected to terminals
40 and 45 for remote reset operation. The switch should have normally open contacts.
Upon the momentary closure of these contacts the 239 will reset any latched alarm,
latched auxiliary relay output, or trip providing it is not locked out. Installing a jumper
wire permanently across the external reset terminals will cause the 239 to reset any
latched alarm or trip whenever motor conditions allow for automatic reset.
•
OPTION SWITCH 1 (41/46) & 2 (42/47): Two option inputs are provided. These switch
inputs are considered active when closed. The state of these input switches can be
monitored by the serial port for process signaling. They can also be programmed to
provide an alarm, trip, alternate motor control setpoints or process control after a
programmable time delay. Programming for these switch inputs, if used, is found in
S4: PROTECTION\SWITCH INPUTS
THERMISTOR INPUT (21/22)
A motor can be equipped with a single thermistor in the end turns or three in the stator
windings for overtemperature detection. Either positive thermal coefficient (PTC) or
negative thermal coefficient (NTC) type thermistors may be directly connected to the 239.
PTC thermistors are preferred because 3 thermistors can be connected in series to monitor
each of the stator phases. This is not possible with NTC thermistors because all three
thermistors must be hot to obtain an indication. Select thermistors that have a resistance
between 100 to 30 000 Ω at the intended alarm/trip temperature. Either linear thermistors
or those with a sharp change in resistance at the required temperature can be used. If no
thermistor sensing is required, these terminals can be left disconnected and the thermistor
feature programmed OFF.
RTDS (OPTION) (48-57)
Up to 3 resistance temperature detectors (RTDs) must be supplied with the motor to use
this option. Verify that the RTD option is installed by noting that the product identification
label on back of the relay includes -RTD in the order code. When ordering a motor with
RTDs, the 100 Ω platinum DIN 43730 type is the preferred choice for optimum sensitivity
and linearity. Other RTDs that can be selected and used with the 239 are 100 Ω nickel, 120
Ω nickel and 10 Ω copper. RTDs do not have to be the same type, however the 239 must be
setpoints.
2–27
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