# Reduction factor for the permissible current rating

For crossing, this is the ratio of the permissibe current when taking into account the presence of crossing heat sources to the permissible current of the insulated cable (derating factor).

For trough, this is the derating factor when using the method according IEE Wiring Regulations, BS 7671

Symbol
$F_{red}$
Formulae
 $\sqrt{- \frac{\Delta \theta_{0x}}{- \Delta \theta_{d} + \Delta \theta_{max}} + 1}$ Crossing $\sqrt{\frac{T_{4iii}}{N_{sys} T_{tr} + T_{4iii}}}$ trough
Related
$\Delta \theta_{0x}$
$\Delta \theta_{d}$
$\Delta \theta_{max}$
$T_{4iii}$
$T_{tr}$
Used in
$I_{c}$