Per the Projects I deal with, a common Electrical Design for Refrigeration Assemblies' Feeders / Branch Circuits is applied as follows:
Manufacturer Specs (using the same values as "SPARKYNC" listed):
Voltage and Phase: 460/3
MCA: 65.68A
MOPD: 110A
(Note: "Fuse or HACR Breaker" is almost never included with the Spec. Values from the MFG.)
1: MCA...
("MCA" = "Minimum Circuit Ampacity")
The MCA is used to determine the Minimum Size of the Branch Circuit Conductors feeding the Equipment.
In this case, #4 THHN CU. will be adequate for an MCA of 65.68A.
2: MOPD...
("MOPD" = "Maximum Over Current Protection Device")
The listed MOPD will determine the Maximum Ampacity for the "Final Overcurrent Protection Device" on this Branch Circuit.
Commonly, the Design parameters I employ, will have a Fusible Disconnect at the Equipment; regardless if the Equipment does or does not include Factory Installed Disconnecting means.
The Fuses at this Disconnect are sized per the MOPD listing.
The MOPD value is 175% of the FUll Load Amperes (FLA) for the Equipment.
This conforms with Section / Table 430.52, for Maximum Rating of a Dual Element (Time-Delay) Fuse.
Using the MOPD of 110 Amps as 175% of the FLA, the Equipment should be rated for 62.7 Amps as the highest draw.
The Fusible Disconnect (Safety Switch) will need to be sized to accommodate a 110 Amp Fuse, which means a 200 Amp Fusible Disconnect Switch
- or more specific;
600 Volt - Heavy Duty,
200 Amp,
3 Pole,
Fusible,
EXO,
NEMA 3R,
with (3) 110 Amp RK5 600VAC Fuses.
MOPD - Part 2...
If the above Fused Disconnect is compliant and acceptable, the Branch Circuit Breaker may be sized to be Maximum 250% the FLA.
Using the FLA of 62.7A, the largest Circuit Breaker trip rating we may use is 150 Amps (62.7 x 2.5 = 156.75), so the (3)#4 THHN CU Branch Circuit Conductors may have -Ground Fault & Short-Circuit Protection- from a 150/3 MCCB.
This is compliant to Section / Table 430.52, for Maximum size of an Inverse Time Circuit Breaker.
(Note: References to Table 430.52 have been applied to the use of Squirrel-Cage Rotor Induction Motors. Wound Rotor and DC Motors have different values in this Table).
Hope these notes are of assistance.
-- Scott
