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Application Note for “Three-Wire Control” with
Hitachi L100 & SJ100 Series Inverters
Sometimes it may be desirable to use a remote START/STOP pushbutton arrangement
together with an inverter. This often occurs when a machine is being retrofitted or
upgraded with the addition of a Hitachi inverter as a replacement for a motor starter. The
pushbuttons that interfaced with the original motor starter would typically be a single-
pole normally-open momentary pushbutton for the START button, and a single-pole
normally-closed momentary pushbutton for the STOP button. Sometimes a switch may
also be present for selecting the forward or reverse direction of rotation.
In the case of the L300P or SJ300 Series of inverters, a function is built-in to directly
interface to a START/STOP pushbutton arrangement of this type without any additional
hardware. Additionally, a FORWARD/REVERSE signal can be accommodated, hence
the term “three-wire” control. The three signals are wired directly to three intelligent
input terminals.
In the case of the L100 and SJ100, such a function is not built in. However the
START/STOP functionality (without direction control, i.e. FWD only) can be
accomplished simply with the addition of a single external control relay, using a circuit
similar to that in the diagram below. This is a simple seal or latch circuit.
L100 or SJ100
Inverter
RUN
STA
P24
IN 1
[FW]
CM1
STP
RUN
24 VDC SPST
Control Relay
L
The above circuit does not include FWD/REV direction change functionality. If this is a
requirement, a more elaborate arrangement is needed. Two relays would be necessary,
and the STOP pushbutton would have to be DPST NC type, as shown in the example that
follows on the next page.