Electric Heater Wiring Schematic - Carrier 39T Installation, Start-Up And Service Instructions Manual

Each heater has 2 different types of factory-installed ther-
mal cutouts for overtemperature protection; an automatic
reset thermal cutout for primary protection and a manual
reset thermal cutout to protect against failure of the primary
system. Also provided is an airflow pressure differential switch
to prevent the heater from operating when the fan is not in
operation or airflow is restricted or insufficient. The primary
automatic reset cutout is a bi-metal disk-type cutout. It is
wired into the control circuit which operates the magnetic
disconnecting contactors (the same contactors which also switch
on and off the various steps of the coil). The secondary manual
reset cutout is a bi-metal disk-type cutout. This secondary
NOTE: All wiring must be copper and must conform to the NEC (National Electrical Code).
Fig. 59 — Electric Heater Wiring Schematic
67
thermal cutout is load carrying and is installed in each heater
subcircuit. The primary and secondary overtemperature pro-
tection systems are independent of each other. The second-
ary system is designed to protect against possible failure of
the primary system to deenergize the heater.
Sub-circuits in the heaters are designed in compliance with
paragraph 424-22 of the NEC. The coil is subdivided into
circuits that draw no more than 48 amps each and is fused
for at least 125% of the circuit rating.
Pitot tube is to be positioned so that the airflow switch is
actuated by a minimum negative pressure of 0.07 in. wg.