Final temperature

Values for maximum temperature of jacket and bedding materials and of screen, sheath and armour materials are specified for following cable elements:

• Insulation materials, defined by $\theta_{cmax}$
• Bedding/serving materials, defined by $\theta_{kmax}$
1. Continuous screen/metallic sheath or non-embedded screen wires or a closed layer of armour wires:
The temperature limits of the screen/metallic sheath/armour when in contact with the oversheath materials, but thermally separated from the insulation by layers of suitable material and sufficient thickness. If thermal separation is not provided, the temperature limit of the insulation should be used if it is lower than that of the oversheath.
2. Embedded spaced screen wires:
The temperature limits of spaced wires when embedded in the oversheath materials, but thermally separated from the insulation of suitable material and sufficient thickness. If thermal separation is not provided, the temperature limit of the insulation should be used if it is lower than that of the oversheath.
• Jacket/oversheath materials, defined by $\theta_{kmax}$
• Current carrying components
1. Conductors:
limited by the insulation material
2. Screen/sheath/armour:
generally limited by the material which it is in contact.
• In the case of screens (except for embedded wires) where there is a layer thermally separating the screen from other material in the cable, a temperature of 350°C should not be exceeded.
• Lead sheath is limited to 170°C and lead alloy to 210°C.
3. Joints and terminations:
Attention should be given to the design and installation of joints and terminations if the short-circuit limits set out are to be safely used.
• Soldered joints should not be used if conductor temperatures > 160°C are contemplated, while welded, compressed or bolted joints allow for 250°C.
• Longitudinal thrust in cable conductors can be considerable, depending on the degree of lateral restraint on the cable, with values up to 50 N/mm$^2$.
• Longitudinal tension in cable conductors is also to be expected after a short-circuit and may exist for a very long period.
• With impregnated paper cables, compound expansion can give rise to considerable fluid pressure and moisture may also be drawn back into the accessory and cable.

Symbol
$\theta_{kf}$
Unit
°C
Formulae
$\left(\theta_{ki}+\beta_k\right) e^{\frac{{I_{kAD}}^2 t_k}{{K_k}^2 {S_k}^2}}-\beta_k$
Related
$\beta_k$
$I_{kAD}$
$K_k$
$S_k$
$t_k$
$\theta_{cmax}$
$\theta_{ki}$
$\theta_{kmax}$
Used in
$I_{kAD}$