Electric Heat Components - Lennox LGA Series Unit Information

E−Optional Electric Heat Components
See ELECTRICAL/ELECTRIC HEAT DATA tables for pos-
sible LCA/LCC to EHA matchups and electrical ratings.
EHA parts arrangement is shown in figures 29 and 30.
All electric heat sections consist of electric heating ele-
ments exposed directly to the airstream. Two electric
heat sections (first section and second section) are
used in all 30kW through 120kW heaters. See figure 28.
Multiple-stage elements are sequenced on and off in re-
sponse to thermostat demand.
HEAT SECTION PLACEMENT
REDUNDANT
HIGH TEMP.
LIMIT S63
FIGURE 28
1−Main Control Box Components
A55, A60, K9, T2, and F4
The main control box (see figure 3) houses a few of the
electric heat controls, such as: the main control module
A55, second electric heat section control panel A60, elec-
tric heat control section for 45 - 120 kW (electric heat
relay K9 and transformer T2), and unit fuse block
F4. For a description of the components see section
I-A.
2−Contactors K15, K16, K17 and K18
Contactors K15, K16, K17 and K18 are all three-pole
double-break contactors located on the electric heat
vestibule. K15 and K16 are located on the first electric
heat section, while K17 and K18 are located on the sec-
ond electric heat section. However, in the 30kW heat-
ers, the first section houses all contactors and fuses. All
contactors are equipped with a 24VAC coil. The coils in
the K15 and K16 contactors are energized by the
main panel A55, while the coil in the K17 and K18
contactors are energized by the electric heat 2 con-
trol panel A60. Contactors K15 and K17 energize
the first stage heating elements, while K16 and K18 ener-
gize the second stage heating elements.
COMPRESSOR
COMPARTMENT
SECOND ELECTRIC
HEAT SECTION
(RIGHT SIDE)
FIRST ELECTRIC
HEAT SECTION
(LEFT SIDE)
Page 49
3−High Temperature Limits S15 and S107 (Primary)
S15 and S107 are SPST N.C. auto-reset thermostats lo-
cated on the back panel of the electric heat section below
the heating elements. S15 is the high temperature limit for
the first electric heat section, while S107 is the high tem-
perature limit for the second electric heat section. Both
thermostats are identical and are wired in series with the
first stage contactor coil. When either S15 or S107 opens,
indicating a problem in the system, contactor K15 is de-
energized. When K15 is de-energized, first stage and all
subsequent stages of heat are de-energized. All
LCA300H/360 electric heat section thermostats are facto-
ry set to open at 170_F + 5_F (76.7_C + 2.8_C) on a tem-
perature rise and automatically reset at 130_F + 6_F
(54.4_C + 3.3_C) on a temperature fall. The thermostats
are not adjustable.
4−High Temperature Limit S63 (Redundant)
S63 is a SPST N.C. manual-reset thermostat located on
the suction line bracket inside the blower compartment
(see figure 28). S63 is a redundant temperature limit fac-
tory installed in all LCA / LCC units. Like the primary tem-
perature limits, S63 is wired in series with the first stage
contactor coil (K15). When S63 opens, all contactors
(K15, K16, K17, K18) are de-energized. When the contac-
tors are de-energized, first stage and all subsequent
stages of heat are de-energized. The thermostat is factory
set to open at 170_F + 8_F (76.7_C + 4.4_C) on a tem-
perature rise and can be manually reset when the temper-
ature falls below 160_F + 6_F (71.1_C + 3.3_C).
5−Terminal Strip TB3
Electric heat line voltage connections are made to termi-
nal strip TB3 (or a fuse block on some models) located in
the upper left corner of the electric heat vestibule.
6−Heating Elements HE1 through HE14
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. See EHA
wiring diagram in WIRING DIAGRAM AND OPERATION
SEQUENCE section in back of this manual. 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.
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 30 and table 5 show the fuses used
with each electric heat section. For simplicity, the ser-
vice manual labels the fuses F3 − 1 through F3 − 8.