Lennox ALLIED Commercial TCA180S2B Standard Manual page 29

D−Optional Electric Heat Components
See ELECTRICAL / ELECTRIC HEAT (table of contents) for
possible TCA to EHA matchups and electrical ratings.
All electric heat sections consist of electric heating ele-
ments exposed directly to the airstream. See figure 1.
Two electric heat sections (first section and second sec-
tion) are used in all 15kW through 90kW heaters used in
TCA180/300 units. Multiple-stage elements are se-
quenced on and off in response to thermostat demand.
EHA parts arrangement is shown in figures 14 and 15.
Control Box Components
The main control box (see figure 12) houses some electric
heat components and the electric heat control hat" sec-
tion (figure 13).
1−Terminal Strip TB15
TB15 distributes line power to the EHA unit, fuse F4, and is
used in all electric heat applications.
2−Fuse F4
Fuse F4 is used only with single point power supply. F4
gives over amperage protection to the compressor and
other cooling components. F4 is located inside a sheet
metal enclosure in the main control box.
Electric Heat Hat Section (Figure 13)
3−Electric Heat Relay K9
All TCA series units with electric heat use an electric heat relay
K9. K9 is a N.O. DPDT pilot relay intended to electrically iso-
late the unit's 24V circuit from the electric heat assembly 24V
circuit. K9 is energized by W1 from the main control board
A45. K9−1 closes, enabling T2 to energize the electric heat.
4−Electric Heat Relay K19
All TCA series units with electric heat use an electric heat relay
K19. K19 is a N.O. SPDT pilot relay intended to electrically
isolate the unit's 24V circuit from the electric heat assembly
24V circuit. K19 is energized by W2 from the main control
board A45 (once K9 is energized). K19−1 closes, enabling T2
to energize the remaining electric heat.
5−Time Delay DL2
DL2 is a solid state timer used in all electric heat units.
DL2 staggers the energizing of the first (W1) and second
(W2) stage heating elements by providing a timed inter-
val. When the timer is de−energizing, the contacts are
delayed 1 second before opening.
ELECTRIC HEAT HAT SECTION
CONTROL BOX
TB15
F4
FIRST
ELECTRIC HEAT
SECTION
ELECTRIC HEAT CONTROL (HAT) ASSEMBLY
TRANSFORMER
T2
Page 29
SECOND
ELECTRIC HEAT
SECTION
FIGURE 12
− 180−300S UNITS
RELAY
K9, K19
TIME DELAY
DL2, DL5
FIGURE 13