Inner Covering & Fillers

For Electrical Cable with a collective metallic layer or Electrical Cable with a metallic layer over each individual cores with additional collective metallic layers, semi-conducting

inner covering and fillers shall be applied over the laid up cores. The inner covering and fillers are made of non hygroscopic material like polypropylene, except if the cable is to be made longitudinally watertight. The inner covering is extruded in general but may be lapped if the interstices between the cores are filled.

The approximate thickness of extruded inner coverings is given in Table 2:

Separation Sheath (for armored cable):

The separation sheath comprises a layer of extruded PVC, PE or LSZH applied over the laid up cores under the armor. PVC is normally of grade ST2 and PE of grade ST7. The nominal thickness is calculated by 0.02Du + 0.6mm

where Du is the fictitious diameter under the sheath in mm. For Electrical Cable without a lead sheath, the nominal separation sheath thickness shall not be less than 1.2mm. For Electrical Cable where the separation sheath is applied over the lead sheath, the nominal separation sheath thickness shall not be less than 1.0mm.

Lapped Bedding (for armored lead sheathed cable):

The lapped bedding applied to the lead sheath consists of either impregnated/synthetic compounded paper tapes or a combination of two layers of these paper tapes followed bya few layers of compounded fabulous materials. The thickness is around 1.5mm.

Armour (for armored cable):

The armor is applied over the inner covering helically. It consists of either flat galvanized steel wire armor (strip), round galvanized steel wire armor, and double steel tape armor.

Over Sheath
Overall sheath comprises a layer of extruded either thermoplastic compound (PVC ST3 type or PE ST7 type or LSZH) or elastomeric compound (polychlorprene CSP or
chlorosulfonated PE). The nominal over sheath thickness is calculated by 0.035D+1 where D is the fictitiuous diameter immediately under the over sheath in mm. For unarmored Electrical Cable and Electrical Cable with the over sheath not applied over the armor, metallic screen or concentric conductor, the nominal over sheath thickness shall not be less than 1.4mm. And for Electrical Cable with over sheath applied over the armor, metallic screen or concentric conductor, the nominal over sheath thickness shall not be less than 1.8mm.