Permissible pull force

The maximum force which may be used is limited by the tensile strength of the conductors or armour wires, or by the gripping capability of the cable stocking, depending on the method used.

When pulling using a stocking/grip, a stocking with the correct diameter and length should be selected, such that all the force is transferred to the conductor(s). After installation it is recommended to cut off two metres beyond the point where the cable stocking/grip was attached and check for no signs of stretching on the sheath.

When the pull is on the armour it shall be confirmed that the sidewall pressure does not exceed that which would occur when using the maximum pull on the conductor in conjunction with the minimum installation bend radius $r_{mbp}$. For example, if the armour pull for a particular cable exceeds the conductor pull by 50% then the minimum bend radius shall also be increased by 50%.

In the case of multi-core cables, the cross sectional area of all conductor cores is taken into account. If multiple cables are pulled at the same time into a common conduit, it is usually assumed that the pulling force does not act on all cables at the same time and a reduced number is considered (e.g. in Switzerland, if three cables are pulled into a common duct only 2 cables are considered being pulled).

Recommendations are not harmonized in the various regions and countries, for example US and Canada consider IEEE Standard 1185 and AEIC Pub G5-90, European countries (UK, Germany, etc.) have similar values for which we refer to VDE. Special requirements or recommendations may apply, and the user might need to adjust the total permissible pull force that is by default calculated as follows:

Number of cablesTotal permissible pull force
One cable$F_{ppc}$
Two cables2 · $F_{ppc}$
Three cables unbound2 · $F_{ppc}$
Three cables triplex3 · $F_{ppc}$
Four cables unbound0.8 · 4 · $F_{ppc}$
Four cables quadruplex4 · $F_{ppc}$
Five cables0.8 · 5 · $F_{ppc}$
Six cables0.8 · 6 · $F_{ppc}$

$f_{ppc} A_c n_c$pull on conductor
$f_{ppc} A_{ar}$pull on armour