Lennox ZCC Series Unit Information page 22

D-Optional Electric Heat Components
Table 3 shows electric heat fuse ratings. See Options/
Accessories section (see table of contents) for ZCC 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 11 and 12.
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 and K9. 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 de-energized.
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 170⁰F + 5⁰F (76⁰C + 2.8⁰C) on a temperature rise and
automatically reset at 130⁰F + 6⁰F (54.4⁰C + 3.3⁰C) on
a temperature fall. For EHA100 units, the electric heat
section thermostat is factory set to open at 160⁰F + 5⁰F
(71.0⁰C + 2.8⁰C) on a temperature rise and automatically
reset at 120⁰F + 6F (49.0C + 3.3⁰C) on a temperature fall.
The thermostat is not adjustable.
3-High Temperature Limit S20, S157, S158, S15, 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 220⁰F + 6⁰F (104⁰C + 3.3⁰C) on a temperature rise
and can be manually reset when temperature falls below
160⁰F (71.0⁰C).
4-Terminal Block TB2
Terminal block 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 Block TB3
Electric heat line voltage connections are made to terminal
block 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.
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