Soil Thermal Resistivity (RHO) in CEC Ampacity Tables

[guiyermo]

Hello,

I have been looking at the Canadian Electrical Code Ampacity Tables for underground circuits, specifically for direct buried installations (Tables D12A to D13B), and I have not been able to find what soil thermal resistivity the calculations are based on.

I am working in a project (in Canada) where the laying of cables in direct buried installations match the ones shown in the Canadian Electrical Code.

I have available the site's soil thermal resistivity and I want to make sure that the ampacity values shown in the tables of the CEC are for a soil thermal resistivy equal or greater than the site's value.

I would like to use these tables instead simulating the same CEC configurations in ETAP's Underground Raceway Module.

I would have used the ampacities shown in IEEE 835 but none of the configurations of this book match our project. I know the CEC used the method shown in IEEE 835 (Neher McGrath) but the RHO is not shown anywhere.

Does anybody have an idea of this?

Also, does anybody know if up to what insulation level the CEC ampacity tables are valid? I am looking at a 28 kV cable.

Thanks for your attention

 

[jghrist]

How do the ampacities compare to the NEC? NEC Tables in Annex B say what RHO is used.

 

[7anoter4]

I think jghrist is right. Compared with nec the earth thermal resistivity could be 90 (Deg. C-cm/watt).