Conductor sizing
Conductor sizing
(OP)
Please advise on the following design situation. We have
adjustable speed drive system which includes drive isolation
transformer, stand alone input AC line reactor after transformer and a conversion unit after AC reactor. Per
NEC-2002, Article 430.22, Exception 2 conductors feeding
"power conversion equipment" should have an ampacity not
less than 125% of rated converter current. The question is whether this factor applies to conductors only for the user
feeder to transformer primary (our system boundary) or also to conductors transformer secondary-AC reactor and AC reactor-power converter?
adjustable speed drive system which includes drive isolation
transformer, stand alone input AC line reactor after transformer and a conversion unit after AC reactor. Per
NEC-2002, Article 430.22, Exception 2 conductors feeding
"power conversion equipment" should have an ampacity not
less than 125% of rated converter current. The question is whether this factor applies to conductors only for the user
feeder to transformer primary (our system boundary) or also to conductors transformer secondary-AC reactor and AC reactor-power converter?





RE: Conductor sizing
Therefore, the industry standards and manufacturer expertise are governing the questioned conductor ampacity sizing.
RE: Conductor sizing
The wires to the transformer primary are a feeder circuit covered in Article 215. Sizing of these conductors and required overcurrent protection is discussed in Article 220.
RE: Conductor sizing
I suspect that the transformer and reactor are manufactured by someone other than the drive manufacturer and have their own nameplates and possibly UL listings, so I would treat these as three separate pieces of equipment.
RE: Conductor sizing
interpretive in NEC.Yes, transformer and reactor are third
party supplied items, UL listed. The question still remains:
they are the inherent part of "power conversion equipment", and Art.430-22 (exc.2) addresses feeder to this "equipment".
RE: Conductor sizing
http://standards.ieee.org/reading/ieee/SB/Jan95/bear-scc31.html
http://www.ewh.ieee.org/soc/pes/icc/subcommittees/subcom_d/wg_d9/wg14_7_biblio.htm
etc. for more info on ampacity
RE: Conductor sizing