Carrier SINGLE PACKAGE ROOFTOP UNITS 48PG20-28 - Manual (Page 11)

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Size gas-supply piping for 0.5-in. wg maximum pressure
drop. Do not use supply pipe smaller than unit gas connection.
Step 9 — Make Electrical Connections
FIELD POWER SUPPLY — Unit is factory wired for volt-
age shown on unit nameplate. Be sure to check for correct
voltage.
When installing units, provide disconnect per NEC (Nation-
al Electrical Code) of adequate size (MOCP [Maximum Over-
current protection] of unit is on the informative plate). See
Tables 4A and 4B. All field wiring must comply with NEC and
local codes. Size wire based on MCA (Minimum Circuit
Amps) on the unit informative plate. See Fig. 15 for power
wiring connection to the unit power terminal block and equip-
ment ground.
Route power and ground lines through control box end pan-
el or unit basepan (see Fig. 4) to connections as shown on unit
wiring diagram and Fig. 15.
Field wiring must conform to temperature limitations for
type “T” wire. All field wiring must comply with NEC and
local requirements.
Operating voltage to compressor must be within voltage
range indicated on unit nameplate. On 3-phase units, voltages
between phases must be balanced within 2%.
Unit failure as a result of operation on improper line voltage
or excessive phase imbalance constitutes abuse and may cause
damage to electrical components.
FIELD CONTROL WIRING — Unit can be controlled with
either a Carrier-approved accessory thermostat. Install thermo-
stat according to the installation instructions included with
accessory. Locate thermostat assembly on a solid interior wall
in the conditioned space to sense average temperature.
Route thermostat cable or equivalent single leads of colored
wire from subbase terminals through conduit into unit to low-
voltage connections as shown on unit label wiring diagram and
in Fig. 16.
NOTE: For wire runs up to 50 ft, use no. 18 AWG (American
Wire Gage) insulated wire (35 C minimum). For 50 to 75 ft,
use no. 16 AWG insulated wire (35 C minimum). For over
75 ft, use no. 14 AWG insulated wire (35 C Minimum). All
wire larger than no. 18 AWG cannot be directly connected at
the thermostat and will require a junction box and splice at the
thermostat.
Do not pressure test gas supply while connected to unit.
Always disconnect union before servicing.
IMPORTANT: Natural gas pressure at unit gas connection
must not be less than 5.5 in. wg or greater than 13.0 in. wg.
The correct power phasing is critical to the operation of the
scroll compressors. An incorrect phasing will result in
compressor shutdown on thermal overload and possible
damage to compressor. Should this occur, power phase cor-
rection must be made to the incoming power.
Unit cabinet must have an uninterrupted, unbroken electri-
cal ground to minimize the possibility of personal injury if
an electrical fault should occur. This ground may consist of
electrical wire connected to unit ground lug in control com-
partment, or conduit approved for electrical ground when
installed in accordance with NEC, ANSI/NFPA (American
National Standards Institute/National Fire Protection Asso-
ciation), latest edition, and local electrical codes. Do not
use gas piping as an electrical ground. Failure to follow
this warning could result in the installer being liable for
personal injury of others.
Fig. 12 — Condensate Drain Details
Fig. 14 — Field Gas Piping
NOTE: Trap should be deep enough to offset maximum unit static
difference. A 4-in. trap is recommended.
Fig. 13 — Condensate Drain Piping Details