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Installation methods

How a cable is installed sets how much current it can carry. Find your installation to see its SS 638:2018 reference method.

Conduit C1–C2

  • THERMAL INSULATION

    C1Ref. Method 4

    Sheathed cables in conduit inside an insulated wall

    • Conduit runs within a thermally insulating wall
    • Conduit touches the inner wall lining on one side

    SS 638 Table 4A, item 6

  • MASONRY / CONCRETE

    C2Ref. Method 3

    Cables in conduit set in masonry or concrete

    • Brick, block, concrete or plaster
    • Not thermal insulation

    SS 638 Table 4A, item 7

Trunking K1–K3

  • WALL

    K1Ref. Method 3

    Cables in trunking on a wall or suspended

    • Surface trunking fixed to a wall, or hung clear of it

    SS 638 Table 4A, item 8

  • FLOOR SCREED

    K2Ref. Method 3

    Cables in flush floor trunking

    • Trunking set into the floor screed, lid flush with the floor

    SS 638 Table 4A, item 9

  • SKIRTING TRUNKING

    K3Ref. Method 3

    Single-core cables in skirting trunking

    • Trunking run along the base of the wall

    SS 638 Table 4A, item 10

Tray T1

  • PERFORATED ≥ 30%

    T1Ref. Method 11

    Sheathed cables bunched on a perforated tray

    • Holes make up at least 30% of the tray surface
    • Cables touching, open to the air

    SS 638 Table 4A, item 11

Free air F1–F3

  • ≥ 0.5 DₑWALL

    F1Ref. Method 12

    Single-core cables spaced in free air

    • Flat, vertical or horizontal: one overall diameter (Dₑ) between cables, at least 0.5 Dₑ from the wall
    • Trefoil: at least 0.5 Dₑ from the wall to the nearest cable, or 0.75 Dₑ to the nearest cables
    • Supports under the cables cover less than 10% of the plan area

    SS 638 Table 4A, item 12

  • > 2 DₑLADDER

    F2Ref. Method 13

    Multicore cables on ladder or brackets

    • Cables more than 2 Dₑ apart
    • At least 0.3 Dₑ from the wall
    • Supports under the cables cover less than 10% of the plan area

    SS 638 Table 4A, item 13

  • CATENARY WIRE

    F3Ref. Method 12 or 13

    Cables hung from a catenary wire

    • Supported by, or built around, a catenary wire
    • Use Method 12 for single cores, 13 for multicores

    SS 638 Table 4A, item 14

Building voids V1–V2

  • THERMAL INSULATION

    V1Ref. Method 4

    Sheathed cables in an insulated wall or above an insulated ceiling

    • Cable laid directly in the insulation, no conduit
    • One side touching a thermally conductive surface

    SS 638 Table 4A, item 15

  • DUCT OR VOID IN STRUCTURE

    V2Ref. Method 4 or 3

    Sheathed cables in ducts or voids in the structure

    • Method 4 when the void is no more than 5 Dₑ across, or its perimeter no more than 20 Dₑ
    • Method 3 for larger voids
    • Perimeter over 60 Dₑ: treat as an enclosed trench (R2–R4)
    • For a group of cables, Dₑ is the sum of their diameters

    SS 638 Table 4A, item 16

Trench R1–R4

  • OPEN / VENTILATED

    R1Ref. Method 12 or 13

    Cables on the wall of an open or ventilated trench

    • Fixed to the trench wall with the spacing of Method 12 or 13

    SS 638 Table 4A, item 17

  • 450 × 300 MIN

    R2Ref. Method 18

    Enclosed trench, 450 mm wide × 300 mm deep or more

    • Depth includes a 100 mm cover
    • Two single cores one diameter apart, or three in trefoil touching
    • Multicores 50 mm apart
    • Apply the enclosed-trench rating factors (Table 4B3)

    SS 638 Table 4A, item 18

  • 450 × 600 MIN

    R3Ref. Method 19

    Enclosed trench, 450 mm wide × 600 mm deep or more

    • Depth includes a 100 mm cover
    • Single cores in flat groups of two or three on the wall, one diameter apart, groups 50 mm apart
    • Multicores 75 mm apart
    • All cables at least 25 mm off the wall; apply Table 4B3 factors

    SS 638 Table 4A, item 19

  • 600 × 760 MIN

    R4Ref. Method 20

    Enclosed trench, 600 mm wide × 760 mm deep or more

    • Depth includes a 100 mm cover
    • Single cores in flat groups or trefoil, groups 50 mm apart
    • Multicores 75 mm apart
    • All cables at least 25 mm off the wall; apply Table 4B3 factors

    SS 638 Table 4A, item 20

Guide only, based on SS 638:2018 Table 4A. Cable selection and sizing should be confirmed by a qualified electrical engineer.

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