Temperature Derate for 5kV Cable

[DGrant041]

My company usually cables generator sets <600 VAC. When med. voltage is required, one of the Tables 310.67 through .86 will apply according to 110.40. These tables are based on 40C (104F) ambient which will suit almost all of our applications.

However, we have a government job (a real one, not just another name for my home projects ) that has a requirement for 120 F ambient for 4160 V generator set.

Here's the part I'm looking at:
310.6 Conductors Rated 2001 to 35,000 Volts

(4) Ambients Not in Tables.
Ampacities at ambient temperatures other than those shown in the tables shall be determined by means of the following formula:
I2 = I1 x sq. rt(TC - TA2 - TD)
                ----------------
                (TC - TA1 - TD)
where:
I 1 = ampacity from tables at ambient TA 1
I 2 = ampacity at desired ambient TA 2
TC = conductor temperature in degrees Celsius (?C)
TA 1 = surrounding ambient from tables in degrees Celsius (?C)
TA 2 = desired ambient in degrees Celsius (?C)
TD = dielectric loss temperature rise

(I hope this turns out legible--I can't copy the formula from the CD ROM since it's a graphic.)

Anyway, does anyone have a link to where this formula is applied? They reference IEEE 835-1994 but I don't have that one available. If it was a NFPA standard I would know where to find it on line but it's not.

Any help would be appreciated.

 

[bob]

I would check with Okonite. http://www.okonite.com/

 

[DGrant041]

Hey bob, thanks for the link.

I bookmarked the "ampacity-correction-factors" page for future reference. The gov't is being especially anal on this project so I was thinking we will probably have to contact the manufacturer since that is their specialty. On the last project we used American Insulated Wire Corp Jumper Cable.

I guess this is one of those areas in the NEC we didn't have to consider before.

Thanks again for your help!

Dale