Overhead Conductor Ampacities Overhead Conductor Ampacities Darmy (Electrical) (OP) 24 Jan 02 12:37 Would anyone have the ampacities for 336 & 556 AAC conductors at 90-95 degrees Fahrenheit? RE: Overhead Conductor Ampacities SphincterBoy (Electrical) 24 Jan 02 12:55 336 KCMILS AAC--495 AMPERES556 KCMILS AAC--680 AMPERESPer Electrical Engineers Handbook, Thirteenth Edition RE: Overhead Conductor Ampacities Darmy (Electrical) (OP) 24 Jan 02 13:05 Thanks a mil! What was the voltage listed? I running at 12.470 KV. RE: Overhead Conductor Ampacities stevenal (Electrical) 24 Jan 02 13:40 EPRI has the same numbers as SphincterBoy, but the temperature given is 40C rise over 40C ambient with 2ft/s crosswind and no sun. Voltage is not relevant. RE: Overhead Conductor Ampacities dpc (Electrical) 24 Jan 02 13:49 I would only add that sometimes the limiting factor is the sag of the conductor and the resulting clearance problems in the middle of the span.dpc RE: Overhead Conductor Ampacities Darmy (Electrical) (OP) 24 Jan 02 17:24 SphincterBoy, who is the Author & Publisher of Electrical Engineers Handbook, Thirteenth Edition you referenced? RE: Overhead Conductor Ampacities redtrumpet (Electrical) 25 Jan 02 13:05 Darmy - 95 F or 95 C? Makes a big difference. The ampacities given in the postings above are way too high for 95 F conductor temp. RE: Overhead Conductor Ampacities Darmy (Electrical) (OP) 25 Jan 02 13:54 redtrumpet, don't you mean too high for 95C. I do want ampacities for 95F. Also could ude the for 1/0 AAC.Thanks for being detailed. I should have been more specific. RE: Overhead Conductor Ampacities stevenal (Electrical) 25 Jan 02 15:33 You wish to run the conductor cooler than the ampacity tables allow, so you will need to run less current. I don't have a formula handy for this derating. Why the temperature limit? The conductors you are asking about are bare, and usually installed overhead, outdoors on insulators that can withstand the heat. RE: Overhead Conductor Ampacities Darmy (Electrical) (OP) 25 Jan 02 15:58 stevenal, that is a typical summer peak temperature here in Colorado. I'm using software called SynerGEE to do summer peak load studies & need correct ampacities for 336, 556, & 1/0 ACC conductors at 95F or even 100F if available. Thanks for your input. Also wish I had the derating formula. One of my co-workers remembers using it 25yrs ago at Consumers Power in Westerm Michigan. RE: Overhead Conductor Ampacities redtrumpet (Electrical) 25 Jan 02 17:54 Darmy - 95 F may be an accurate ambient temperature, but you need to specify a temperature rise or maximum conductor temperature to get a meaningful ampacity. 95 F is 35 C, so be on the safe side and assume a 40 C ambient. Temperature rise could be anywhere from 10 C to 60 C under normal conditions depending on the conditions for which the line was designed. There are current-temperature rise graphs for ampacity in the Aluminum Electrical Conductors Handbook. You should also take into account emissivity of the conductor (how black it is, basically), whether sun is present, wind speed, altitude (this is Colorado, right?), etc.All the above takes some work to calculate, even more if you are going to account for emergency loading at higher temperatures which will sag your conductor as dpc pointed out, so most people cop out and use a table. The one I have handy (Hubbell/Anderson Technical Data) says 400 A for 336.4 kcmil AAC based on 61% IACS aluminum alloy, average temperature rise 30 C above 40 C ambient, horizontal, 60 Hz, outdoors, 2 fps wind, minimum 18" spacing. No mention of sun or emissivity.Different tables will be based on different conditions and hence will have different ampacities. I have seen ampacities from tables differ by up to 50%. No offence, but it sounds like you don't have the technical background to come up with a meaningful ampacity number. Better start talking to your distribution engineers. RE: Overhead Conductor Ampacities SphincterBoy (Electrical) 28 Jan 02 08:58 Darmy, the Electrical Engineers Handbook is a must have.It is published by McGraw-Hill.There is now a fourteenth edition.The authors are Donald G. Fink, and H. Wayne BeatyI also use SynerGEE too. I think it is the bestfor mapping, but for one-line analysis, it is pathetic. RE: Overhead Conductor Ampacities stevenal (Electrical) 28 Jan 02 16:01 Since the 90-95 F is an ambient temperature rather than a conductor temperature, sphincterboy's ampacities should suit. www.southwire.com is also a good reference. Ampacities are slightly different. RE: Overhead Conductor Ampacities kraigb (Electrical) 29 Jan 02 10:50 Most of the line designs I have seen base the ampacity on a guess as to what the worst case ambient air temperature would be for the area in which the line will be installed. 90-95 degF (32-35 degC) is a little unusual, but not outside the summertime operating temps we might expect to see. I think a typical design ambient air temperature is 40 DegC (104 degF), and a conductor temperature of either 75degC or 90degC.The conductor temperatures are selected based on the clearances between the lines and from ground level. You basically pick your mounting heights and sags taking into account a worst case ambient temp and the operating conditions you expect on the line.Sooo, here's some numbers I ran on my OH line ampacity software for the listed conditions.Conductor: 336.4 Merlin35 degC (95degF)2 ft/sec crosswind3000 ft eleveation38 degrees latitude11:00am in sun440 amps for 75 degC conductor temp520 amps for 90 degC conductor tempConductor: 336.4 Merlin40 degC (104degF)2 ft/sec crosswind3000 ft eleveation38 degrees latitude11:00am in sun406 amps for 75 degC conductor temp497 amps for 90 degC conductor tempWithout doing a lot of digging for your 556 AAC conductor, I don't know the exact properties, but I have on hand information on 559.5 Aluminum (Codeword Darien), if that is close enough for your needs.Conductor: 559.5 Darien35 degC (95degF)2 ft/sec crosswind3000 ft eleveation38 degrees latitude11:00am in sun560 amps for 75 degC conductor temp672 amps for 90 degC conductor tempConductor: 559.5 Darien40 degC (95degF)2 ft/sec crosswind3000 ft eleveation38 degrees latitude11:00am in sun516 amps for 75 degC conductor temp637 amps for 90 degC conductor tempThe software uses the calculation method suggested in IEEE 738-1993. That IEEE standard would be a good reference on OH conductor ampacity if you haven't already looked at it.Please remember that the ambient conditions are really your ruling factors for conductor ampacity, so you should design for worst case to be safe. Hope this helps a little. RE: Overhead Conductor Ampacities stevenal (Electrical) 29 Jan 02 11:19 Merlin is an ACSR conductor, Darien is AAAC. The steel core of the Merlin, and the alloy strands of the Darien reduce the ampacity per KCM compared with AAC (all aluminum). Try code words Mistletoe and Dalia for the 556KCM, and Tulip for the 336. RE: Overhead Conductor Ampacities CUman (Electrical) 20 Jun 02 13:20 I am interesting in whether or not you have to derate bundled conductor as opposed to single conductor. In other words do you just double the ampacity of the single conductor if it's bundled. Any thoughts?