Ampacity rating Aluminum Conductors 25kV

[Edmo513]

Hello,

New EE here. Does anyone know the ampacity rating for a 1/0 aluminum conductor @ 90 degrees Celsius? The conductor is rated at 25kV and it is being connected to a 300 KVA transformer. The conductor will be installed underground. Also I don't know if the conductor is either stranded or solid.

Thank you.

 

[Compositepro]

The ampacity due to thermal limits does not change with voltage.

 

[bacon4life]

The ampacity depends on the type of burial. The generic calculation from the Okonite catalog lists the ampacity as 155 amps to 215 amps depending on the type of installation. Keep in mind you would need to adjust the rating based on your actual conditions and conductor.

Other than a busbar, I have not encountered a solid conductors as large as 1/0. Usually for small conductors stranding has a small (i.e. negligible) impact on ampacity. For very large conductor sizes, the skin effect means larger diameter conductors would have a larger ampacity for a give cross sectional area of conductor. These large sizes are never solid, and the choice between 7/17/37 strands has little impact on total diameter or ampacity. If the strand cross-sections are not round, there would be a difference in diameter and ampacity. Compact construction (i.e. trapezoidal wire) has a lower ampacity per volume of aluminum and expanded construction(i.e. gap type) has a higher ampacity per volume of aluminum.

 

[waross]

Ampacity depends on the ability of a conductor to reject of the I²R heat developed in the conductor.
Consider the ampacity of a number 10 AWG conductor.
If you connect four #10 AWG conductors in parallel you will have four times the cross sectional area, four times the surface area and four times the ampacity.
Noe if you combine the four #10 AWG conductors into one conductor you will still have four times the cross sectional area but only twice the surface area.
The surface area versus cross sectional area and the ability to reject heat have much more effect than skin effect or stranding on ampacity.
Tubular bus versus solid bus gains ampacity in two ways. Less skin effect and much more surface area to reject heat.


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Ohm's law
Not just a good idea;
It's the LAW!

 

[7anoter4]

See NEC 2017 [2020] Art 310.60 Table 310.60 (C)(82) det 9