With my company being acquired and the subsequent e-mail address change, the listserver didn’t recognize me so I’m sending.
________________________________ From: Radojicic, Marko Sent: Monday, February 02, 2009 1:24 PM To: 'Kunde, Brian'; [email protected] Subject: RE: De-Rating Hookup Wire Brian, To address your questions: - Your derating process is correct according to NEC. You have to add all the derating factors at the same time. - I don’t believe that you have to derate for self-heating (the 10C factor in your calculation). The correction factors at the bottom of Tables 310-16 and 310-17 specifically state “ambient temperatures”. The self-heating is what the ampacity calculation takes into account. - Tie-wrapping wires together = bundling. - No further derating for length of wire. Voltage drop is an issue, like you state. - Make sure you are using the correct table if the wires are in raceways. For example, Table 310-16 is for “Raceway, Cable, or Earth (Directly Buried)” while 310-17 is for “Free-Air”. - I looked through my 1999 version of NEC and was unable to find how you got the initial ampacity rating. I don’t see any mention of 105C insulation at 10 AWG. Could you let me know how you got that? …Marko ________________________________ From: [email protected] [mailto:[email protected]] On Behalf Of Kunde, Brian Sent: Monday, February 02, 2009 11:48 AM To: [email protected] Subject: De-Rating Hookup Wire I want to make sure I’m properly de-rating the current capacity of hook-up wire. A 105º hookup wire size 10 AWG is rated 58 amps at 30ºC. At 50ºC (40ºC out side temp and 10ºC internal temp rise) I have to de-rate by .86 which would now make it handle only 49.9 amps. If I bundle 2 to 5 wires together, I have to de-rate another .8 which would make it only rated for 39.9 amps. So do I de-rate the de-rated value or is there some other method that is more correct? What is considered a “Bundle”? If I cable tie 2 wire together is this considered a bundled? Is there an additional de-rating for wire length of hookup wire? I assume wire length only affected voltage drop, not current rating. Thanks to all for your help. The Other Brian _________________________ LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. Important : This message is intended only for the recipient(s) identified above by the originator or forwarder of this message and may contain information that is confidential, proprietary and/or legally privileged. 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