NoVA Comms Power
Senior Member
- Location
- Alexandria, VA
Hello all:
I've been an "active lurker" and infrequent poster for many years (and have attended Mike's seminars in person)
My question deals with a VFD and motor integrated into a single chiller by a large, well-known, and reputable chiller manufacturer
All amperage values are approximate as the actual values are irrelevant to my actual question.
Equipment Detail:
Motor Nameplate FLA: 392 A
VFD Nameplate Input: 780 A
(Note that both nameplates are mounted on the unit)
One school of design thought is that the branch conductors led to the VFD should have an ampacity of 975A (1.25 x the VFD's "nameplate" 780) per NEC 430.122.
However, the manufacturer insists -- after repeated queries -- that the ampacity of branch conductors need only be 490A (1.25 * 392) based on their interpretation of NEC 440.33.
The manufacturer has also declined to "remove" the nameplate of the VFD (i.e. so have single "common" nameplate for the entire integrated chiller)
The branch conductor design is at a bit of a quandary over which way to proceed.
Q: What IS the "right" interpretation?
Q: Specifically, does specific guidance by the manufacturer of an integrated unit take precedence over the individual "unintegrated" component nameplates?
I hope that we might obtain some true "3rd party" interpretation of the NEC from this forum.
Looking forward to any and all replies and to the discussion this question might generate.
I've been an "active lurker" and infrequent poster for many years (and have attended Mike's seminars in person)
My question deals with a VFD and motor integrated into a single chiller by a large, well-known, and reputable chiller manufacturer
All amperage values are approximate as the actual values are irrelevant to my actual question.
Equipment Detail:
Motor Nameplate FLA: 392 A
VFD Nameplate Input: 780 A
(Note that both nameplates are mounted on the unit)
One school of design thought is that the branch conductors led to the VFD should have an ampacity of 975A (1.25 x the VFD's "nameplate" 780) per NEC 430.122.
However, the manufacturer insists -- after repeated queries -- that the ampacity of branch conductors need only be 490A (1.25 * 392) based on their interpretation of NEC 440.33.
The manufacturer has also declined to "remove" the nameplate of the VFD (i.e. so have single "common" nameplate for the entire integrated chiller)
The branch conductor design is at a bit of a quandary over which way to proceed.
Q: What IS the "right" interpretation?
Q: Specifically, does specific guidance by the manufacturer of an integrated unit take precedence over the individual "unintegrated" component nameplates?
I hope that we might obtain some true "3rd party" interpretation of the NEC from this forum.
Looking forward to any and all replies and to the discussion this question might generate.