543.1.3

From this earlier thread: https://communities.theiet.org/discussions/viewtopic/1037/27055?post_id=149445#p149445


If it helps at all I've taken this from Paul Cook's Commentary on the IEE Wiring Regulations 16th Ed (OK I know it's old, but the underlying physics won't have changed)


k = √ ( (σ_c ( β + 20 ) x 10 ^-12) / ρ₂₀ ) ln ( (θ_f + β) / (θ_i + β) ) )


(hopefully I've got the brackets right)


Where σ_c is the volumetric specific heat capacity of the conductor at 20°C. (e.g. 3.45 x 10⁶ J/Km³for copper)

β is the reciprocal of temperature coefficient of resistance of the conductor at 0°C (e.g. 234.5 K for copper)

ρ₂₀ is the electrical resistivity of the conductor at 20°C (e.g. 1.7241 x 10^-8 Ωm for copper)

θ_f is the final temperature (°C)

θ_i is the initial temperature (°C)

ln is the natural logarithm (log_e)

  - Andy.

Suggest you get a new son Zoom!