Overhead Conductor Ampacities 1

[Darmy]

Would anyone have the ampacities for 336 & 556 AAC conductors at 90-95 degrees Fahrenheit?

 

[SphincterBoy]

336 KCMILS AAC--495 AMPERES

556 KCMILS AAC--680 AMPERES

Per Electrical Engineers Handbook, Thirteenth Edition

 

[Darmy]

Thanks a mil! What was the voltage listed? I running at 12.470 KV.

 

[stevenal]

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.

 

[dpc]

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

 

[Darmy]

SphincterBoy, who is the Author & Publisher of Electrical Engineers Handbook, Thirteenth Edition you referenced?

 

[redtrumpet]

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.

 

[Darmy]

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.

 

[stevenal]

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.

 

[Darmy]

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.

 

[redtrumpet]

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.

 

[SphincterBoy]

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 Beaty

I also use SynerGEE too. I think it is the best
for mapping, but for one-line analysis, it is pathetic.

 

[stevenal]

Since the 90-95 F is an ambient temperature rather than a conductor temperature, sphincterboy's ampacities should suit.

http://www.southwire.com

is also a good reference. Ampacities are slightly different.

 

[kraigb]

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 Merlin
35 degC (95degF)
2 ft/sec crosswind
3000 ft eleveation
38 degrees latitude
11:00am in sun
440 amps for 75 degC conductor temp
520 amps for 90 degC conductor temp

Conductor: 336.4 Merlin
40 degC (104degF)
2 ft/sec crosswind
3000 ft eleveation
38 degrees latitude
11:00am in sun
406 amps for 75 degC conductor temp
497 amps for 90 degC conductor temp

Without 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 Darien
35 degC (95degF)
2 ft/sec crosswind
3000 ft eleveation
38 degrees latitude
11:00am in sun
560 amps for 75 degC conductor temp
672 amps for 90 degC conductor temp

Conductor: 559.5 Darien
40 degC (95degF)
2 ft/sec crosswind
3000 ft eleveation
38 degrees latitude
11:00am in sun
516 amps for 75 degC conductor temp
637 amps for 90 degC conductor temp

The 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.

 

[stevenal]

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.

 

[CUman]

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?