Compressed Air Best Practices - January 2009 - (Page 32)

| 01/09 Focus Industry ENERGY REBATES | M I N I M U M S U P P LY W I R E S I Z E R E C O M M E N D A T I O N S F O R C O M P R E S S O R PA C K A G E S U T I L I Z I N G VA R I A B L E F R E Q U E N C Y D R I V E S Based on the example above, if a wire run length of 100 feet of 75 ºC copper wire is used and all terminal connection points are rated for a minimum of 75 ºC, then copper wire size number 1 AWG can be used for this application as it is rated for 130A at 30 ºC ambient which meets the minimum package conductor amperage requirement of 125A. Keep in mind that the length of the wire run to the compressor is important as it directly affects voltage drop. Most drive applications utilize 40 ºC or 45 ºC for ambient temperature conditions. These conditions require conductor ampacity correction(s) to allow for the higher temperatures. The NEC requires that conductor sizes for use in other than 30 ºC ambient temperature be determined by using the appropriate multiplier listed at the bottom section of NEC Table 310.16, and selecting the conductor size that has sufficient ampacity, after correction(s), to meet the load requirements. Conductor ampacity is to be corrected, not “Package Amps.” An example of this procedure, utilizing the example shown above, is as follows: p The 1 AWG copper conductors referenced, above, are rated for 130 amperes based on an ambient temperature of 30 ºC and a conductor temperature rating of 75 ºC. For 40 ºC ambient conditions, the 75 ºC conductor ampacity correction factor is 0.88 resulting in the 1 AWG copper conductor ampacity being corrected from 130 amperes at 30 ºC to 114.4 (130 x .88) amperes at 40 ºC ambient. Number 1 AWG wire is not sufficient for this application at 40 ºC because the corrected conductor ampacity is less than the required minimum of 125 amperes. For 45 ºC ambient conditions, the 75 ºC conductor ampacity correction factor is 0.82 resulting in the 1 AWG copper conductor ampacity being corrected from 130 amperes at 30 ºC to 106.6 (130 x .82) amperes at 45 ºC ambient. Number 1 AWG wire is not sufficient for this application at 45 ºC because the corrected conductor ampacity is less than the required minimum of 125 amperes. p p 32 www.airbestpractices.com http://www.airbestpractices.com

Table of Contents Feed for the Digital Edition of Compressed Air Best Practices - January 2009

Compressed Air Best Practices - January 2009 Contents From the Editor Utility-Air News Compressed Air Audit of the Month: A Nitrogen Audit at Boeing Air Standards: New ASME & ISO Standards for Compressed Air System Assessments Energy Rebates Assist Industrial Sustainability Initiatives Seven Sustainability Projects for Industrial Energy Savings: Project #1: Lighting Optimization Minimum Supply Wire Size Recommendations for Compressor Packages Utilizing Variable Frequency Drives The Pneumatic Advantage: Pneumatics Bring Precision and Reliability to Furniture Industry Specialist Personal Productivity: Is Afternoon Fatigue Influencing Your Job Performance? The Explanation and Some Solutions. Resources for Energy Engineers: Training Calendar & Product Picks Wall Street Watch Advertiser Index Classifieds

Compressed Air Best Practices - January 2009

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.