Page 30
6−Time Delay DL5
Time delay DL5 is identical to DL2. DL5 further staggers
the (W2) second stage heating elements by providing a
timed interval between the energizing of the elements
activated by DL2 and elements activated by DL5.
7−Electric Heat Transformer T2
All TCA series units with electric heat use a single line
voltage to 24VAC transformer mounted in the electric
heat control hat section in the control box. The transform-
er supplies power to all electric heat controls (contactors
and coils). The transformer is rated at 70VA and is pro-
tected by a 3.5 amp circuit breaker CB13 located on the
body of T2. The 208/230 (Y) voltage transformers use
two primary voltage taps as shown in figure 3. Transform-
er T2 is identical to T1.
Electric Heat Sections
8−Contactors K15, K16, K17 and K18
Contactors K15, K16, K17 and K18 are all three-pole
double-break contactors located on the electric heat vesti-
bule. K15 and K16 are located on the first electric heat sec-
tion, while K17 and K18 are located on the second electric
heat section. However, in the 15 and 30kW heaters, the first
section houses all contactors and fuses. All contactors are
equipped with a 24VAC coil. The coils in the K15, K16, K17
and K18 contactors are energized by the main panel
A45. Contactors K15 and K17 energize the first stage
heating elements, while K16 and K18 energize the second
stage heating elements.
9−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 15 and table 8 show the fuses used with each
electric heat section. For simplicity, the service manual la-
bels the fuses F3 − 1 through F3 − 8.
10−Terminal Strip TB3
Electric heat line voltage connections are made to terminal
strip TB3 (or a fuse block on some models) located in the up-
per left corner of the electric heat vestibule.
11−High Temperature Limits S15 and S107
(Primary)
S15 and S107 are SPST N.C. auto-reset thermostats located
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 temperature 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.
The thermostats used on EHA360-45-1 Y/G/J are factory set
to open at 200
_
F + 5
_
F (93.3
_
C + 2.8
_
C) on a temperature
rise and automatically reset at 160
_
F + 6
_
F (71.1
_
C + 3.3
_
C)
on a temperature fall. All other electric heat section thermo-
stats are factory set to open at 170
_
F + 5
_
F (76.7
_
C + 2.8
_
C)
on a temperature rise and automatically reset at 130
_
F + 6
_
F
(54.4
_
C + 3.3
_
C) on a temperature fall. The thermostats are
not adjustable.
12−Heating Elements HE1 through HE14
Heating elements are composed of helix wound bare nich-
rome wire exposed directly to the airstream. Three elements
are connected in a three-phase arrangement. The ele-
ments in 208/230V units are connected in a Delta" ar-
rangement. Elements in 460 and 575V units are con-
nected 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.
