Electric Heaters; Single Point Boxes And Supplementary Fuses; Safety Devices - Bryant Legacy 547K Service And Maintenance Instructions

ELECTRIC HEATERS

The 547K units can be equipped with field-installed accessory
electric heaters. The heaters are modular in design, with heater
frames holding open coil resistance wires strung through ce-
ramic insulators and control contactor(s), using a combination
of 24-v control side break/auto-reset or line-break/auto-reset
limit switches and a pilot-circuit/manual reset limit switch to
protect the unit against over-temperature situations. All 547K
Model electric heaters are one module containing either one or
two banks of electric heat coils.
Heater modules are installed in the compartment below the in-
door (supply) fan outlet. Access is through the indoor access
panel. Heater modules slide into the compartment on tracks
along the bottom of the heater opening. See Fig. 34-36.
Fig. 34 — Typical Access Panel Location
OPTIONAL
FACTORY- MAIN SINGLE
CONTROL POINT
INSTALLED
DISCONNECT BOX BOX
CONTROL WIRE
TERMINAL BLOCK
Fig. 35 — Typical Component Location
Fig. 36 — Typical Module Installation
INDOOR
ACCESS
PANEL
CONTROL BOX
ACCESS PANEL
CENTER VANE AXIAL
POST INDOOR FAN
SYSTEM
MANUAL
RESET
LIMIT
SWITCH
HEATER
HEATER
MOUNTING
COVER
BRACKET
HEATER
MODULE
Not all available heater modules can be used in every unit. Use
only those heater modules that are UL listed for use in a specif-
ic size unit. Refer to the label on the unit cabinet regarding
approved heaters.

Single Point Boxes and Supplementary Fuses

When the unit MOCP device value exceeds 60A, unit-mounted
supplementary fuses are required for each heater circuit. These
fuses are included in accessory single point boxes, with power
distribution and fuse blocks. The single point box will be
installed directly under the unit control box, just to the left of
the partition separating the indoor section (with electric heat-
ers) from the outdoor section. The single point box has a
hinged access cover. See Fig. 37.
CONTROL WIRING
FOAM POWER
WIRING
Fig. 37 — Typical Single Point Installation
On 547K units, all fuses are 60A. Single point boxes contain-
ing fuses for 208/230-v applications use UL Class RK5 250-v
fuses (Bussmann FRNR 60 or Shawmut TR 60R). Single point
boxes for 460-v and 575-v applications use UL Class T 600-v
fuses (Bussmann JJS 60 or Shawmut A6T 60). (Note that all
heaters are qualified for use with a 60A fuse, regardless of ac-
tual heater ampacity, so only 60A fuses are necessary.)

Safety Devices

CRHEATERS323A00 - 341A00 electric heater applications
use a combination of 24-v control side break/auto-reset, line-
break/non-resettable "one shot" limit switches and a fan sta-
tor/manual reset limit switch to protect the unit against over-
temperature situations.
Line-break/auto-reset limit switches, 24-v control side
break/auto-reset and line-break/non-resettable "one shot" limit
switches are mounted on the base plate of each heater module.
See Fig. 38. These are accessed through the indoor access
panel. Remove the switch by removing two screws into the
base plate and extracting the existing switch.
Fan stator/manual reset limit switch is located in the side plate
of the indoor (supply) fan housing. See Fig. 38.
21
HEATER HEATER
RELAY MOUNTING SCREWS