| A common question received on the Hotline
is whether it is acceptable to break only one wire with a pressure
switch, float switch or probe system? As a water system's primary
operating control, the control switch senses when to turn off the
water supply, either by pressure or level. Improperly wired switches
may lead to control box or submersible motor failure.
When connecting the power supply to a Franklin submersible
motor and control box, all local, state and national codes must
be followed. The National Electrical Code (NEC) states in section
430-84: "The controller shall not be required to open all conductors
to the motor." However, the preferred method of supplying power
to a Franklin submersible 2-wire or 3-wire motor is to break both
incoming power lines before the control box on a 3-wire with your
control device.
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| Typically, using a control device which only breaks
one line does not cause a problem. However, if the wire which is interrupted
develops a ground fault or insulation breakdown between the control
device and the motor, the uninterrupted wire will supply low voltage
to the motor and/or control box thru the ground fault (i.e., a 230
volt supply would have 115 volts to ground). This low voltage can
cause premature failure of the motor and control box components. A
submersible motor and control box will try to run as long as the low
voltage is available. However, it will typically draw high amps and
eventually fail. Breaking both lines eliminates this potential problem
by removing all power from the control box and motor. This can be
done with most standard control switches or floats.
If you are using a float switch or control switch
that only has one set of contacts, then you can use a 2-pole magnetic
contactor or relay. When a magnetic contactor or relay is used,
the coil voltage of the contactor is controlled by the original
switch, float or probe. The power supply to the motor or control
box is supplied through the contacts of the relay or contactor.
Another problem when only one line is broken is
that a voltage potential may exist at the control box or motor,
even though the control device is open. This could cause a work
hazard during repair.
Only breaking one line to control a submersible
motor is done frequently, typically meets National Electrical Code
requirements and may meet local codes. However, it is not the preferred
method for the reasons mentioned. You should interrupt both in-coming
power legs whenever possible.
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