Thermal diffusivity is a parameter describing the ability of soil to transfer heat throughout its volume.

**Used for calculating Soil Ambient Temperature and for cable Cyclic Rating Factors**.

If no data is available on the soil then a standard value to use for soil thermal diffusivity is **0.5 x 10^-6** (m^2/s) which corresponds roughly to a soil having a thermal resistivity of 1 K.m/W and a moisture content of around 7 % of dry mass.

Can be estimated from soil thermal resistivity according to Table II from Standard IEC 853-1 [1] below:

Can be calculated according to the below equation (IEC 853-1) [1]:

**References:**

[1] IEC 60853-1, First edition 1985, Calculation of the cyclic and emergency current rating of cables Part 1: Cyclic rating factor for cables up to and including 18/30 (36) kV

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