5
Theory of Operation - Electrical
Electrical Requirements
The electrical requirements for the SMT Central Pressure Cleaning
system depends on the SMT model installed. Regardless of model,
all central systems must be powered by a dedicated circuit with a
Ground Fault Circuit Interrupter (GFCI) breaker in the main breaker
panel. Electrical service requirements are:
2000REY: (Nema L630R) 208/230 Volt, 30 Amp rated for wet locations
at the unit.
600REY/WCY: (NEMA 6-15R) 208/230 Volt, 20 Amp Rated for wet
location at the unit.
Line voltage to the system is supplied from the dedicated outlet
through power cord into the SMT Master Control Panel (MCP) to
the input side of contactor K3.
Motor Drive Circuit
Refer to Figures 2 and 4 (
schematic and wiring diagram of the SMT
electrical circuits
). When contactor K3 is energized by the control
circuit, the line voltage is applied through the contactor to the
motor. The motor starts up, drives the pump and produces water
flow.
Control Circuits
Control circuits within SMT central systems are 24 Volt AC low
voltage. The control circuits include the 24V AC power circuit,
water condition sensors circuit, remote stations circuit, motor
control circuit, chemical control circuits and the line pressure
release circuit.
24V AC power circuit
provides low voltage AC for all control
circuits. Line voltage to the system is picked off of the contactor
line terminals and applied through fuse (FI) to the multi-tap input
of the 24V transformer (T1). F1 requires a ¼ amp slow-blow fuse
for 208 and 230 volt inputs. Voltage is applied to Transformer (T1)
through one of three leads of the primary winding. The multi-tap
primary leads permit system operation on 208 or 230 volts AC.
The 24V output is routed through 3 amp circuit breaker (CB1)
to the 24V AC Power indicator (LI) and the rest of the control
circuits. Current flow through all circuits returns to the transformer
through the 24V AC return line. The 24V AC is connected to Float
Switch (SW1), Remote Station Power Relay (K1), Motor Drive Relay
(K2), and to the Line Pressure Release Solenoid (SOL 3).
Water condition sensor circuits
provide protection to the pump
when adverse water conditions exist. The sensors will remove
power from the remote stations when the water supply level is
too low or water temperature exceeds 120° F. Float Switch (SW1)
is closed when the water level in the float tank is above the
minimum operating level for the pump, completing the circuit
through Thermal Limit Switch (SW2) which will energize Relay (K1)
and apply power to all Remote Stations (RMT-*). Thermal Limit
Switch (SW2) is normally closed. When water temperature within
the system exceeds 120°F, Thermal Limit Switch (SW2) will open
and remove power from the remote stations.
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