Optional Electric Heat Components - Lennox KHA SERIES Manual

D−Optional Electric Heat Components
Electric heat matchups are found in the ELECTRICAL
DATA tables. See table of contents.
All electric heat sections consist of electric heating ele-
ments exposed directly to the airstream. See figure 11.
See figure 12 for vestibule parts arrangement.
1−Contactors K15, K16
All contactors are double break and either single,
double or three pole (see diagram) and equipped with
a 24VAC coil. The coils in the K15 and K16 contactors
are energized by the indoor thermostat. In all units
K15 energizes the heating elements, while in the 22.5
kW units, K15 and K16 energize the heating elements
simultaneously.
2−High Temperature Limits S15 (Primary)
S15 is a SPST N.C. auto-reset thermostat located on the
back panel of the electric heat section above the heating
elements. S15 is the high temperature limit for the electric
heat section. When S15 opens, indicating a problem in the
system, contactor K15 is de-energized (including K16 in
22.5 kW units). When K15 is de-energized, all stages of
heat are de-energized. See table 3 for S15 set points. Set
points are factory set and not adjustable.
TABLE 3
Unit kW (Voltage)
S15 Opens ° F
7.5 (Y, G, J, P)
10 (P)
15 (Y)
15 (G, J, P)
22.5 (Y, G, J)
22.5 (P)
3−High Temperature Limit S20 and S157 (Secondary)
S20 and S157 are SPST N.C. manual-reset thermo-
stats. S20 and S157 are wired in series with the heating
elements. See T1EH wiring diagrams. When either
limit opens K15 and K16 are de-energized. When the
contactors are de-energized, all stages of heat are de-
energized. The thermostat is factory set to open at
220_F + 6_F (104_C + 3.3_C) on a temperature rise
and can be manually reset when temperature falls be-
low 160_F (71.0_C). See figure 12 for location.
4−Terminal Strip TB2
Terminal strip TB2 is used for single point power instal-
lations only. TB2 distributes power to TB3. Units with
multi−point power connections will not use TB2.
S15 Closes ° F
160 120
170 130
170 130
160 120
160 120
150 110
5−Terminal Strip TB3
P and Y voltage units are equipped with terminal strip
TB3. Electric heat line voltage connections are made
to TB3, which distributes power to the electric heat
components and is located on the vestibule. See fig-
ure 12.
6−Heating Elements HE1 through HE6
Heating elements are composed of helix wound bare
nichrome wire exposed directly to the airstream. Three
elements are connected in a three-phase arrange-
ment. The elements in 208/230V units are connected
in a Delta" arrangement. Elements in 460 and 575V
units are connected in Wye" arrangement. Each stage
is energized independently by the corresponding contac-
tors located on the electric heat vestibule panel. Once
energized, heat transfer is instantaneous. High temper-
ature protection is provided by primary and redundant
high temperature limits and overcurrent protection is
provided by fuses.
ELECTRIC HEAT ELEMENTS
7−Fuse F3 and F42
Fuse F3 and F42 are housed in a fuse block which holds
two or three fuses. Each F3 fuse is connected in series
with each leg of electric heat. Figure 12 and table 4 show
the fuses used with each electric heat section.
8−Unit Fuse Block & Fuse F4
Unit fuses F4 provide short circuit and ground fault
protection to all cooling components in the KHA units
with electric heat. The fuses are rated in accordance
with the amperage of the cooling components. The F 4
fuse block is located inside a sheetmetal enclosure.
Page 29
FIGURE 11