Electric Heaters; Connect Power And Control Wires - Carrier 39T Installation, Start-Up And Service Instructions Manual

Electric Heaters —
Electric heaters are factory in-
stalled. If special circumstances require field installation of
heaters, follow the instructions given below.
The heater can only be installed in the EHS1 electric heat
section. To install horizontal electric heater, refer to Fig. 58
and proceed as follows:
1. Locate electric heat section already mounted on unit and
remove protective shipping cover.
2. Locate crate containing electric heater and verify heater
matches the unit. Unit hand and heater hand must agree.
3. Remove both knockout slugs (power and control). Install
conduit connectors. Correct size holes must be drilled or
punched in control box as specified in Fig. 58.
4. Remove top panel of the electric heat section and drill 2
holes as specified in Fig. 58.
5. Insert the electric heater into unit. The heater must slide
between 2 angles located on the bottom of the section.
6. Secure heater to the electric heat section by inserting screws
through frame (12 to 18 screws are required).
7. Locate top panel of section. Run conduit through top panel
and tighten conduit connectors. Lower top panel and re-
place panel on unit.
8. Complete wiring per wiring diagram and job require-
ments. Follow all applicable local codes.
LEGEND
LH — Left-Hand
RH — Right-Hand
Fig. 58 — Electric Heater Installation — Horizontal
CONNECT POWER AND CONTROL WIRES — Heater
wiring schematic is located on control box panel. (Figure 59
shows typical wiring details.) Electrical data for each
standard heater arrangement is shown in Table 22. Verify that
minimum airflow requirement (minimum coil face velocity,
fpm) will be met, especially on applications where variable
air volume is supplied.
Use copper power supply wires rated for 75 C minimum.
On 250-v or greater applications, use 600-v rated wiring. Size
wires to carry 125% of current load on each set of terminals
(Table 23). Use the following formulas as required:
Single-phase line current
(kW per set of terminals) (1000)
=
voltage
Three-phase line current
(kW per set of terminals) (1000)
=
(voltage) (1.73)
Note that if the heater is rated at 50 kW (or more) and is
controlled by a cycling device such as a multi-stage
thermostat, or a step controller, conductors may be sized
at 100% of load amperes (as in Tables 22 and 23) per NEC
Section 424-22. Heater construction and application in-
formation (Tables 22 and 23) are based upon Space Heat-
ing Standard UL No. 1096 and the requirements of the
NEC. Installer is responsible for observing local code
requirements.
Install a disconnect switch or main circuit breaker in
accordance with NEC and other applicable codes. Locate so
that it is easily accessible and within sight of heater control
box (per NEC Article 424-19 and 424-65).
Weatherproof junction boxes have no knockouts for wire
entrance. Provide knockouts for all wiring using field-
supplied grommets of correct size and type of conduit as
required.
Where field-supplied thermostats are used, isolate circuits
to prevent possible interconnection of control circuit wiring.
Where field-supplied step controller is used, connect steps
to terminals as marked on wiring schematic. When connect-
ing multi-stage heaters, wire stage no. 1 so that it is first stage
on, last stage off.
Provide sufficient clearance for convection cooling of heat-
ers with solid-state controllers. Provide at least 5-in. of free
air space above and below cooling fins extending from heater
terminal box. Be sure to connect interlock terminals F1 and
F2 to auxiliary contacts on fan starter.
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