Specifications
JOHNSON CONTROLS
2-42
FORM 102.20-N1 (1109)
Installation
ELECTRICAL INSTALLATION
1. Follow the wiring diagram on the inside of the
terminal box.
2. Supply connections must be made with copper
wiring rated for 75° C minimum.
3. If supply connections are for 250 volts or greater,
all wiring must be insulated for 600 volts.
4. When making line connections to heater element
terminals FOR FINNED TUBULAR HEATERS
ONLY, apply a 1/4" wrench to at section of termi-
nal immediately below threads. Otherwise damage
to terminal may result.
5. Supply conductors for heaters rated less than 50
KW, must be sized at 125% of rated load. On heat-
ers rated 50 KW and more, the supply conductors
may be sized at 100% of rated load, if indicated
on the wiring diagram. The line current for either
a single or three phase load is calculated as fol-
lows:
Voltage
Voltage x 1.73
6. The following table shows the maximum current
for 75 °C copper wire with not more than 3 con-
ductors in a raceway. It is based on the National
Electrical Code Table 310-16. The amperages
shown are for 125% and 100% wire sizing. If there
are more than 3 conductors in a raceway, derate
these amperages per Table 310-15(b)(2)(a).
MAXIMUM CURRENT FOR COPPER WIRING
AMPS WIRE
SIZE
AWG/
MCM
AMPS WIRE
SIZE
AWG/
MCM
AMPS WIRE
SIZE
AWG/
MCM
125% 100% 125% 100% 125% 100%
12 14 80 100 3 184 230
16 12 92 115 2 204 255 250
24 10 104 130 1 228 285 300
40 8 120 150 0 248 310 350
52 65 6 140 175 268 335 400
68 85 4 160 200 304 380 500
7. When connecting heaters with more than one stage,
wire stage No. 1 so that it is the rst stage on and
the last stage off.
8. The heater must be wired so that it cannot operate
unless air is owing over it. This can be accom-
plished by using a built-in airow switch and a
remote interlock. See the accompanying wiring
diagram for the method used with this heater and
provide appropriate interlock wiring as illustrated.
This diagram will be located inside of the electric
heater control panel.
9. If not supplied as part of this heater, install a
line disconnect switch or main circuit breaker in
accordance with the National Electrical Code.
Depending upon the heater’s location and acces-
sibility, a built-in disconnect switch may meet this
requirement.
10. All electrical connections in the heater, including
both eld and factory made connections, should be
checked for tightness before operating the heater.
In addition, after a short period of operation, all
connections should again be checked for tight-
ness.
11. If heater is wired to a heating / cooling thermostat,
use a thermostat with isolating circuits to prevent
possible interconnection of Class 2 outputs.
12. If the heating elements are divided into several
sections with resistance wire between two or more
sections, maximum KW per sq. ft. should be cal-
culated as follows: