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1. A field supplied disconnect switch must be installed at or
near the unit in accordance with the National Electrical
Code (NEC latest edition). Refer to the “Power Wire Siz-
ing & Protection Device Equations” (DSS calculation), for
determining the correct size.
2. Location for the electrical service entrance is illustrated in
Figure 3-2. Complete the unit’s power wiring connections
onto the main terminal block 1TB1 inside the unit control
panel. Refer to the customer connection diagram that
shipped with the unit for specific termination points.
3. Provide proper grounding for the unit in accordance with
local and national codes.
Table 3-4
Customer Connection Wire Range
Power Wire Sizing and Protection Device Equations
To correctly size the main power wiring for the unit, use the appropriate calculation(s) listed below. Read the load definitions
that follow and use Calculation #1 for determining the MCA (Minimum Circuit Ampacity), MOP (Maximum Over current Pro-
tection), and RDE (Recommended Dual Element fuse size) for each unit. Use Calculation #2 to determine the DSS (Discon-
nect Switch Size) for each unit.
Load Definitions: LOAD 1 = CURRENT OF THE LARGEST MOTOR (COMPRESSOR OR FAN MOTOR)
LOAD 2 = SUM OF THE CURRENTS OF ALL REMAINING MOTORS
LOAD 4 = CONTROL POWER TRANSFORMER
= AND ANY OTHER LOAD RATED AT 1 AMP OR MORE
Calculation #1
(MCA, MOP, and RDE)
MCA = (1.25 x LOAD 1) + LOAD 2 + LOAD 4 MOP = (2.25 x LOAD 1) + LOAD 2 + LOAD 4
Select a fuse rating equal to the MOP value. If the MOP value does not equal a standard fuse size as listed in NEC 240 - 6,
select the next lower standard fuse rating.
Note: If selected MOP is less than the MCA, then select the lowest standard maximum fuse size which is equal
to or larger than the MCA, provided the selected fuse size does not exceed 800 amps.
RDE = (1.5 x LOAD 1) + LOAD 2 + LOAD 4
Select a fuse rating equal to the RDE value. If the RDE value does not equal a standard fuse size as listed in NEC 240 - 6
select the next higher standard fuse rating.
Note: If the selected RDE is greater than the selected MOP value, then select the RDE value to equal the MOP
value.
Calculation #2
Disconnect Switch Sizing (DSS)
DSS = 1.15 X (LOAD 1 + LOAD 2 + LOAD 4)
Installation (Continued)
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