All Franklin three-phase submersible motors are suitable
for full-voltage starting. Under this condition the motor
speed goes from zero to full speed within a half second
or less. The motor current goes from zero to locked rotor
amps, then drops to running amps at full speed. This
may dim lights, cause momentary voltage dips to other
electrical equipment, and shock power
In some cases the power companies may require
reduced-voltage starters to limit this voltage dip. There
are also times when reduced-voltage starters may be
desirable to reduce motor starting torque thus reducing
the stress on shafts, couplings, and discharge piping.
Reduced-voltage starters also slow the rapid acceleration
of the water on start-up to help control upthrust and
Reduced-voltage starters may not be required if the
maximum recommended cable length is used. With
maximum recommended cable length there is a 5%
voltage drop in the cable at running amps, resulting in
about 20% reduction in starting current and about 36%
reduction in starting torque compared to having rated
voltage at the motor. This may be enough reduction in
starting current so that reduced-voltage starters are
Three-Lead Motors: Autotransformer or solid-state
reduced-voltage starters may be used for soft-starting
standard three-phase motors.
When autotransformer starters are used, the motor should
be supplied with at least 55% of rated voltage to ensure adequate starting torque. Most autotransformer
starters have 65% and 80% taps. Setting the taps on
these starters depends on the percentage of the
maximum allowable cable length used in the system.
If the cable length is less than 50% of the maximum
allowable, either the 65% or the 80% taps may be used.
When the cable length is more than 50% of allowable,
the 80% tap should be used.
Six-Lead Motors: Wye-Delta starters are used with
six-lead Wye-Delta motors. All Franklin 6" and 8"
three-phase motors are available in six-lead Wye-Delta construction.
Consult the factory for details and availability. Part winding
starters are not compatible with Franklin Electric submersible
motors and should not be used.
Wye-Delta starters of the open-transition type, which
momentarily interrupt power during the starting cycle, are
not recommended. Closed-transition starters have no
interruption of power during the start cycle and can be
used with satisfactory results.
Reduced-voltage starters have adjustable settings
for acceleration ramp time, typically preset at 30
seconds. They must be adjusted so the motor is at
full voltage within THREE SECONDS MAXIMUM to
prevent excessive radial and thust bearing wear.
If Subtrol-Plus or SubMonitor is used the
acceleration time must be set to TWO SECONDS
MAXIMUM due to the 3 second reaction time of the
Subtrol-Plus or SubMonitor.
Solid-state starters AKA soft starts may not be compatible with Subtrol-Plus/SubMonitor. However, in some cases a bypass contactor has been used. Consult the factory for details.
During shutdown, Franklin Electric's recommendation is for the power to be removed, allowing the pump/motor to coast down. Stopping the motor by ramping down the voltage is possible, but should be limited to three (3) seconds maximum.