Conductor sizing

[thinker]

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?

 

[jbartos]

Suggestion: NEC normally covers the safety requirement outside of the manufactured product. NEC does not have jurisdiction inside of the manufactured product. The manufactured product safety is normally covered by industry standards, e.g. UL, NEMA, etc.
Therefore, the industry standards and manufacturer expertise are governing the questioned conductor ampacity sizing.

 

[QUIPPDUDE]

NEC Article 430.22 is applied to all conductors between the transformer secondary and the motor.
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.

 

[dpc]

If these components are stand-alone with field-installed wiring between them, then I'd assume this wiring must comply with the NEC, unless the supplier wants to pay for a UL field certification of the entire assembly.

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.

 

[thinker]

Gents, thank you for your inputs. As I expected, opinions are different,thus confirming that the issue is quite
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".

 

[jbartos]

Suggestion: Visit

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

 

[Shortstub]

Have you checked the Code & Standards issue forum group?