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F-Optional Electric Heat Components
Tables 7 through 9 show all possible LCA to EHA matchups
and electrical ratings.
EHA parts arrangement is shown in figure 25. All electric
heat sections consist of electric heating elements ex-
posed directly to the airstream. Multiple-stage elements
are sequenced on and off in response to thermostat de-
mand.
1-Contactor K15
All EHA electric heat sections are equipped with
K15, located on the electric heat faceplate. Four dif-
ferent N.O. contactors are used for K15. All four con-
tactors have slightly different ratings: two are three-
pole double-break
single-throw. The contactor used depends upon the
size and voltage of the heat section. K15 is
equipped with a 24VAC coil which is energized on
first-stage heat demand (W1). When K15 is ener-
gized, the heating elements (first-stage heating ele-
ments if equipped with multi-stage heater) are ener-
gized.
2-Contactor K16
Contactor K16 is used in all the 7 through 25 kW
single-phase and EHA72-20/25/30-1-Y electric
heat sections. K16 is located on the electric heat
faceplate. Four different N.O. contactors are used
for K16. All four contactors have slightly different
ratings: two are three-pole double-break and two
are single-pole single-throw. The contactor used
depends upon the size and voltage of the heat sec-
tion. K16 is equipped with a 24VAC coil which is en-
ergized on second-stage heat demand (W2) in all
single-phase electric heat sections. When K16 is
energized, the second-stage heating elements are
energized.
3-Contactor K17
Contactor K17 is used in all the 15 through 25 KW
single-phase electric heat sections, and is located in
the electric heat faceplate. Two different SPST N.O.
contactors are used for K17. Each has a slightly differ-
ent rating. The contactor used depends upon the size
of the heat section. K17 is equipped with a 24VAC coil
which is energized on second-stage heat demand
(W2). When K17 is energized, the third-stage heating
elements are energized.
and two are single-pole
4-High Temperature Limits S15 (Primary)
S15 is a SPST N.C. auto-reset thermostat located on the
electric heat section . S15 is the high temperature limit for
the electric heat section. When S15 opens, indicating a
problem in the system, contactor K15, K16 and K17 is de-
energized.
5-High Temperature Limit S20 (Secondary)
S20 is a SPST N.C. non-reusable "one time" limit. Like
the primary temperature limit, S20 is wired in series with
the first stage contactor coil (K15) and second stage con-
tactor coil (K16) and (K17). When S20 opens, contactors
(K15, K16and K17) 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 at185_F + 7 _F (85_C + 3.8_C) on a temper-
ature rise and must be replaced once the limit opens.
6-Heating Elements HE1, HE2, HE3, HE4, HE5, HE6
HE1 and HE2 are used in all EHA units. HE3 is used
in 15 through 25kW single phase electric heat sec-
tions. HE4, HE5 and HE6 are used in 20 and 25kW
single phase electric heat sections. Heating ele-
ments are composed of helix wound bare nichrome
wire exposed directly to the airstream. Heating ele-
ments are energized directly by contactors on the
EHA faceplate. Once energized, heat transfer to the
air stream is instantaneous. Overtemperature
protection is provided by primary and secondary
high temperature switches. Overcurrent protection
is provided by current limiting fuses.
7-Electric Heat Sub-Fuse Box EHAFB
EHAFB series fuse box assembly (figure 24) is re-
quired for single disconnect switch application and
provides fuse protection for both the EHA series heat-
ers and the LCA unit. The EHAFB contains F3 and F4
fuses. F3 fuses protect the electric heat section while
F4 fuses protect the unit. F3 is a current-limiting fuse
connected in series with each leg of electric heat
(each stage of electric heat uses three fuses). F4 is
also a current-limiting fuse, but it is connected in se-
ries with unit line voltage L1, L2, and L3. F4 fuses and
fuse block are ordered separately and field installed.
Page 31
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