Cable Sizing NEC vs IEC 3

[NickParker]

What is the standard practice of calculating cable size in Oil & Gas Industry? What are the differences between IEC cable sizing vs NEC cable sizing?
Where can I find the derating factors for cable grouping, ambient temperature, Soil temperature and soil thermal resistivity.
NEC provides a cable grouping derating factors in 310.15(B)(2)(A) and for temperature, it could be found in 310.16, while I could not find derating factors for soil temperature and soil thermal resistivity. Should I ask these derating factors from the cable manufacturer (or) Are are there any standards that can provide the derating factor.
We are using cables which are manufactured according to IEC, but to be used in Oil & Gas Industry in Saudi Arabia.

 

[Mbrooke]

What code are you useing there to begin with, IEC or NEC? If NEC convert the values in tables 310 to mm2, then select the larger IEC standard size. Remember to keep track of the IEC cable temperature listing.

 

[ScottyUK]

IEC 60364 is the international standard, but most countries have their own wiring regulations which may or may not reference the IEC standard. In the UK we have BS 7671, in Australia there is AS3000, and so on. The IEC document contains derating tables, as do the national standards.

In the Middle East an ambient of 50°C was a design requirement, and we provided sunshields to prevent direct isolation of cable racks and equipment. I don't recall the design ground temperature but I suspect it will be at least 30°C.

 

[7anoter4]

For low voltage cable current carrying capacity[ampacity]-as Scotty already said-IEC 60364-5-52 Selection and erection of electrical equipment –Wiring systems
and national standards as BS 7671, DIN-VDE 0276-603 and other. For medium voltage cable up 35 kV, IEC 60502-2 Annex B[informative], Norme Francaise HN-33-S-52, DIN-VDE 0276-620 and other. One may calculate the ampacity according to IEC 60287-1-1 and 2-1 [or according Neher and McGrath, of course].
However, in my opinion, a large number of software exist and may support you in any case.

 

[leur2011]

1- Ampacity calculation and cable sizing can be as per NEC, or from the tables in IEEE 835, or IEC 60364, and IEC 60502-2.

2- Cable derating factors of ETAP or CYME can be use to calculate ampacities, as an alternative to the NEC, IEC or IEEE 835 tables.

3- Soil temperature is 40°C. The soil thermal resistivity (RHO) is 120°C-cm/watt for direct buried, 85°C-cm/watt for concrete ductbank.

4- Vendor can provide derating factors of their own cables to be installed underground and aboveground. Different vendor obviously have different values of correction and derating factors though. Normally base temperature rating 30°C of cable is varying depend on standard use to manufacture cable.

5- Cable sizing can be as per IEC 60287, IEC 60364, and IEC 60502-2. If cable specify as per NEC then you need to use NEC for evaluating the cable ampacity; or vice versa.

 

[IanTsai]

Yes there's a list of coefficient between temperature and cable resistance, and cable resistance is a key factor to decide ampacity.
I am from a cable factory and we always calculate cable size by ampacity, we got a list to convert both value.