Power Wire Sizing And Protection Device Equations - Trane IntelliPak CG-SVX02B-EN Installation & Operation Manual

Air-cooled cold generator, "k" and later design sequence, with 3-dtm scroll compressors

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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

Calculation #1

(MCA, MOP, and RDE)

MCA = (1.25 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.

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)

= AND ANY OTHER LOAD RATED AT 1 AMP OR MORE

RDE = (1.5 x LOAD 1) + LOAD 2 + LOAD 4

DSS = 1.15 X (LOAD 1 + LOAD 2 + LOAD 4)

Installation

MOP = (2.25 x LOAD 1) + LOAD 2 + LOAD 4

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