Table 1: Maximum sensor cable lengths and wire sizes
Wire
gauge
1
Maximum Sensor cable length
22 AWG
125 ft (40 m)
1
At the listed maximum cable lengths, there is less than 1Fº
(0.6Cº) error between the temperature sensed at the A99
sensor and the temperature displayed on the LCD.
TB2 Terminal Block and SPDT relay output
The terminals LC, LNO, and LNC on the TB2 terminal block
connect to an SPDT dry-contact relay in the A421 Control
(Figure 3). The control does not provide any internal
power to the TB2 terminals or relay contacts. The A421
Control energizes and de-energizes the relay to open
and close the contacts based on the On/Off temperature
values.
• Relay De-energized (Off) = LC open to LNO as shown in
Figure 3, and the relay status LED is off
• Relay Energized (On) = LC closed to LNO and the relay
status LED is on
Figure 4 shows how to wire the A421 Control to use the
same power source that powers the controlled equipment
to also power the A421 Control.
Figure 3: TB2 Terminal Block showing connections to
the internal SPDT relay
You can also provide an independent power source for the
A421 Control on the TB1 terminals and then wire the TB2
relay terminals to a separate power source to switch and
power the controlled equipment circuit.
Figure 4: Wiring the A421 Series Controls using the
same power source to power the control operation and
power the controlled equipment
Table 2: A421 Control Wiring Terminals and wire size
information
Terminal
block
Label Description, function, and
requirements
Wire sizes
LN
Line-voltage power source
(common): Connect the neutral
wire for 120 VAC supply power
applications. Connect the L1 supply
power lead for all 208/240 VAC
supply power applications.
120V
Line-voltage 120 VAC control power
(hot): Connect the 120 VAC supply
power (hot) for 120 VAC supply
power applications (using jumper
from LC in Figure 4).
TB1
120/240
VAC
Models
240V
Line-voltage 240 VAC control
power (L2) terminal: Connect
the L2 supply power connection
for 208/240 VAC supply power
applications (using jumper from LC
28 AWG to
12 AWG
0.08 mm² to
4.0 mm²
LC
Line-voltage SPDT relay common
contact: Connect power supply to
power the controlled load.
Connect 120 VAC (hot) for 120 VAC
applications.
Connect L2 for 208/240 VAC
applications.
LNO
Line-voltage SPDT relay normally
open contact: Connects controlled
equipment to the line-voltage
normally open (LNO) contact on
the SPDT relay. When LC is closed
to LNO, the relay is energized
and the green LED is on. The
LNO terminal typically provides
power to the controlled equipment
in both cooling and heating
applications.
TB2
LNC
Line-voltage SPDT relay normally
closed contact: Connects controlled
equipment to the line-voltage
normally closed (LNC) contact on
the SPDT relay. When LC is closed
to LNC, the relay is de-energized
and the green LED is off. The LNC
terminal is not typically wired to
the controlled equipment.
28 AWG to
12 AWG
0.08 mm² to
4.0 mm²
BIN
Detects a switch closure between
the BIN and COM terminals and
overrides the control to turn the
fan on. Normal control resumes
after this switch is opened again.
COM
Connects the low-voltage common
from the sensor and binary input.
TB3
SEN
Connects the low-voltage input
signal wire from control sensors.
22 AWG
(0.34 mm²)
stranded,
shielded
cable
A421 Series Electronic Temperature Controls with Cycle Timer Installation Guide
4
