Lennox KCC Series Unit Information page 24

D-Optional Electric Heat Components
Table 3 shows electric heat fuse ratings. See Options/
Accessories section (see table of contents) for KCC to
EHA match-ups. See Electrical/Electric Heat Data section
(see table of contents) of this manual for electrical ratings
and capacities.
All electric heat sections consist of electric heating
elements exposed directly to the air stream. See figure
12. EHA parts arrangement is shown in figures 12 and
13. Multiple-stage elements are sequenced on and off in
response to thermostat demand.
1-Contactors K15, K16
Contactors K15 and K16 are three-pole double-break
contactors located on the electric heat vestibule. All
contactors are equipped with a 24VAC coil. The coils in the
K15 and K16 contactors are energized by a W2 thermostat
demand, K9, and DL2. Contactor K15 energizes the first
stage heating elements, while K16 energizes the second
stage heating elements.
2-High Temperature Limits S15 (Primary)
S15 is a SPST normally closed auto-reset thermostat
located on the back panel of the electric heat section below
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 deenergized.
When K15 is de-energized, first stage and all subsequent
stages of heat are de-energized. For EHA102/150 units,
the electric heat section thermostat is factory set to
open at 170F + 5F (76C + 2.8C) on a temperature rise
and automatically reset at 130F + 6F (54.4C + 3.3C) on
a temperature fall. For EHA100 units, the electric heat
section thermostat is factory set to open at 160F + 5F
(71.0C + 2.8C) on a temperature rise and automatically
reset at 120F + 6F (49.0C + 3.3C) on a temperature fall.
The thermostat is not adjustable.
3-High Temperature Limit S20, S157, S158, S159, S160
& S161 (Secondary)
Limits are SPST normally closed manual-reset thermostat
like the primary temperature limit, S20 is wired in series
with the first stage contactor coil (K15) and second stage
contactor coil (K16). When S20 opens, contactors (K15,
K16) are de-energized. When the contactors are de-
energized, first stage and all subsequent stages of heat
are de-energized. The thermostat is factory set to open
at 220F + 6F (104C + 3.3C) on a temperature rise and
can be manually reset when temperature falls below 160F
(71.0C).
4-Terminal Strip TB2
Terminal strip TB2 is used for single point power
installations only. TB2 distributes L1, L2 and L3 power to
TB3. Units with multi-point power connections will not use
TB2.
5-Terminal Strip TB3
Electric heat line voltage connections are made to terminal
strip TB3 located in the upper left corner of the electric
heat vestibule. TB3 distributes power to the electric heat
components.
6-Heating Elements HE1 through HE6
Heating elements are composed of helix wound bare
nichrome wire exposed directly to the air stream. Three
elements are connected in a three-phase arrangement.
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 contactors located on
the electric heat vestibule panel. Once energized, heat
transfer is instantaneous. High temperature protection
is provided by primary and redundant high temperature
limits and overcurrent protection is provided by fuses.
7-Fuse F3
Fuse F3 are housed in a fuse block which holds three
fuses. Each F3 fuse is connected in series with each leg
of electric heat. Figure 17 and table 3 show the fuses used
with each electric heat section. For simplicity, the service
manual labels the fuses F3 - 1, 2 and F4 - 1, 2.
8-Unit Fuse Block F4
Three line voltage fuses F4 provide short circuit and ground
fault protection to all cooling components in the KCC units
with electric heat. The fuses are rated in accordance with
the amperage of the cooling components.
ELECTRIC HEAT CONTROL ASSEMBLY
1-Electric Heat Relay K9
All KCC series units with electric heat use an electric
heat relay K9. K9 is a N.O. DPDT pilot relay intended to
electrically isolate the unit's 24V circuit from the electric
heat 24V circuit. K9 is energized by CMC1. K9-1 closes,
energizing timer DL2. K9 is located in the electric heat
control assembly. See figure 11.
ELECTRIC HEAT CONTROL ASSEMBLY
Page 24
ELECTRIC HEAT
CONTROL ASSEMBLY
ELECTRIC HEAT
SECTION
K9
FIGURE 11
DL2