diagram and notes

diagram and notes
2 Wire Control Of Star Delta Starters For Pressure,
Temperature And Similar Control Applications
Important: This diagram is a functional schematic of the control method.
The installer must familiarise themselves with any national or local electrical
and safety directives and legislation relevant to this type of installation and
application. Such issues are not covered here and it remains the responsibility
of the installer to ensure that the requirements of such legislation and
directives are met.
Notes on the attached diagram:
The object of this design is to provide a circuit design which provides 2 wire control of a Star
Delta circuit, as may be required for simple close contact/open contact operation as one
would frequently find when to be operated by pressure switch, thermostat, etc.
One of the key features of this design is that it retains important aspects of 3 wire control, ie
push button control for On/Off, not of the motor itself but the control circuit. Additionally, it
provides “No Volt Release” of the control circuit, meaning that on resumption of power after a
supply interruption, the motor will not unexpectedly restart. It will require the positive act of
pressing the start button to re-activate the control circuit.
Stop control can be achieved by pressing the stop/reset button on the overload relay (which
will open contact 95/96) or by the addition of any number of remote Stop buttons, wired in
series, in the control supply line to terminal 95 on the overload relay
KM1 = Star Contactor
KM2 = Line Contactor
KM3 = Delta Contactor
Control Relay is to activate the control circuit and provide “No Volt Release” of the control
signal.
Schematic for 2 wire control of Star Delta Starter
eg Pressure or temperature control
Control Supply
95
Overload
Relay
96
Start
Button
Control Relay
Pressure Switch
21
13
KM2
KM3
22
14
21
13
KM1
KM1
14
22
67
55
Timer
KM2
Timer
KM2
56
Control
Relay
KM1
68
KM2
KM3
IMPORTANT: Read accompanying notes before
considering use of this scheme
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