Hello all,
I wish to discuss scenarios involving a Refrigeration Condenser Unit, and the Branch Circuit OCPD, Feeder (Branch Circuit), plus Disconnecting means at the Equipment.
Our example CU will be as follows:
- 460V 3Ø;
- FLA = 78.2 Amps;
- MCA = 93.2 Amps;
- MOPD = 125 Amps;
- Compressor(s) are _NOT_ Hermetic Refrigerant Motor-Compressor: Open frame Motor drives Compressor via external shaft;
- Across-The-Line Motor Starting;
- Circuit length less than 100 feet from Service Equipment;
- CU runs less than 180 Minutes at any given time (non-continuous load).
What are your thoughts on the following Four (4) examples?:
------------------------------------------------------------
Example #1:Nameplate references MOPD (Maximum Overcurrent Protection Device) as "Maximum Fuse Or HACR Circuit Breaker" = 125 Amp.
A: Branch Circuit Conductors = Three (3) #2 THHN CU, + 1 #6 CU EGC (Equipment Grounding Conductor).
B: 200 Amp, 3 Pole, 600V Fusible Disconnect Switch at CU, with Three (3) 125 Amp RK5 Fuses.
C: Branch Circuit Breaker = 200/3
Is this example (Example #1) NEC Compliant?
Is it a "Good Design"?
Please contribute your thoughts.
------------------------------------------------------------
Example #2:Nameplate references MOPD (Maximum Overcurrent Protection Device) as "Maximum Fuse Or HACR Circuit Breaker" = 125 Amp.
A: Branch Circuit Conductors = Three (3) #2 THHN CU, + 1 #6 CU EGC (Equipment Grounding Conductor).
B: 200 Amp, 3 Pole, 600V _NON-FUSIBLE_ Disconnect Switch at CU.
C: Branch Circuit Breaker = 125/3 (HACR)
Is this example (Example #2) NEC Compliant?
Is it a "Good Design"?
Please contribute your thoughts.
------------------------------------------------------------
Example #3:Nameplate references MOPD (Maximum Overcurrent Protection Device) as "MAXIMUM FUSE" = 125 Amp.
A: Branch Circuit Conductors = Three (3) #2 THHN CU, + 1 #4 CU EGC (Equipment Grounding Conductor).
B: 200 Amp, 3 Pole, 600V Fusible Disconnect Switch at CU, with Three (3) 125 Amp RK5 Fuses.
C: Branch Circuit Breaker = 225/3
Is this example (Example #3) NEC Compliant?
Is it a "Good Design"?
Please contribute your thoughts.
------------------------------------------------------------
Example #4:Nameplate references MOPD (Maximum Overcurrent Protection Device) as "Maximum Overcurrent Protection Device" = 125 Amp. (no references to "Fuse" or "HACR Circuit Breaker")
A: Branch Circuit Conductors = Three (3) #2 THHN CU, + 1 #6 CU EGC (Equipment Grounding Conductor).
B: 200 Amp, 3 Pole, 600V Fusible Disconnect Switch at CU, with Three (3) 125 Amp RK5 Fuses.
C: Branch Circuit Breaker = 225/3
Is this example (Example #4) NEC Compliant?
Is it a "Good Design"?
Please contribute your thoughts.
------------------------------------------------------------
I pose these examples for Two reasons:
1: To stir up some discussions on the subject;
2: To verify past designs I have dealt with.
Looking forward to your replies.
Thanks in advance.
Scott
