Carrier Aero 39MN Series Installation, Start-Up And Service Instructions Manual page 154

protect against possible failure of the primary system to deen-
ergize the heater.
Subcircuits 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.
NOTE: Airflow tube is to be positioned so that the airflow
switch is actuated by a minimum negative pressure of 0.07
in. wg. In the event that the minimum 0.07 in. wg cannot be
achieved, extend the high pressure tube to the next
upstream bulkhead to the fan discharge for draw-thru elec-
tric heat or extend the low pressure tube to the negative side
of the fan for blow-thru electric heat.
Refer to Table 40 for heater electrical data.
a39-1721
NOTE: All wiring must be copper and must conform to the NEC (National Electrical Code).
Fig. 129 — Electrical Heater Wiring Schematic (Typical)
Table 39 — Field Wiring for Incoming Conductors
Sized for 125% of Heater Load
WIRE SIZE LOAD AMPS*
(AWG OR
COPPER
KCMIL)
14
12
10
8
6
4
3
2
1 104
1/0 120
LEGEND
AWG — American Wire Gage
kcmil — Thousand Circular Mils
NEC — National Electrical Code
*Values are based on Table 310-16 of the NEC for 75 C insulated
copper wire. Not more than 3 conductors in a raceway.
NOTES:
1. Be sure to consider length of wiring run and possible voltage
drops when sizing wires.
2. Field power wiring — Heaters are furnished with a terminal
block sized for incoming copper conductors with 75 C insulation
rated to carry at least 125% of the heater load. However, con-
ductors can be sized to carry 100% of the heater load if the
heater is rated at 50 kW or more, and the heater is controlled by
a cycling device such as a multi-stage thermostat, step control-
ler, or SCR (silicon control rectifier) power controller. Terminal
blocks and knockouts are sized to handle either 100% or 125%
conductors.
154
WIRE SIZE LOAD AMPS*
(AWG OR
KCMIL)
12
2/0
16 3/0
24 4/0
40 250
52 300
68 350
80 400
92 500
600
700
COPPER
140
160
184
204
228
248
268
304
336
368