inner jacket<\/em> — overall O.D. on request<\/td>\n| LBSDMX-8CH and the 4–48 channel range<\/td>\n<\/tr>\n<\/table>\n Two families deserve a note before any conduit is chosen. The shielded network constructions are physically larger than the unshielded ones — Cat6A UTP is published at 6.2–7.2 mm while Cat6A SFTP 10G is published at 8.0 mm — so the same conduit holds noticeably fewer shielded cables. And the flat speaker constructions are oval, not round, which the next section handles.<\/p>\n The fill arithmetic<\/h2>\nThe rule is about area, not diameter, so two 6 mm cables do not take the space of one 12 mm cable: nine 6 mm cables fit in the cross-section of one 18 mm cable. Convert every cable to an area first.<\/p>\n \n- Cable area = π × (O.D. ÷ 2)² — a 6.4 mm cable is 32.2 mm².<\/li>\n
- Conduit internal area = π × (internal diameter ÷ 2)² — a conduit with a 25 mm internal diameter is 490.9 mm².<\/li>\n
- Allowable cable area = conduit internal area × fill percentage.<\/li>\n<\/ul>\n
Worked example.<\/strong> Six runs of Cat6A UTP at 6.4 mm into a conduit with a 25 mm internal diameter. Cable area 32.2 mm² × 6 = 193.0 mm². Allowable at 40 % = 490.9 × 0.40 = 196.3 mm². The six cables fit — with 3.3 mm² of headroom, which is 1.7 % of a single cable. Any seventh cable, a batch at the top of its tolerance, or a tighter conduit puts the run over the limit. That is what a borderline answer looks like, and it is the reason to compute rather than estimate.<\/p>\nThe fill percentages exist for pulling friction and for heat, not for neatness: a conduit that is nearly full cannot be pulled without strain on the jacket, and it cannot shed heat from the conductors inside. Where a run has bends, a long pull, or a mix of cable sizes, the practical answer is always smaller than the table below.<\/p>\n How many cables fit<\/h2>\nComputed from the published outside diameters above at a 40 % fill, for straight runs. The row is the cable’s overall O.D.; the column is the conduit’s internal<\/em> diameter, which is smaller than its trade size.<\/p>\n\n\n| Cable O.D.<\/th>\n | 20 mm ID<\/th>\n | 25 mm ID (≈1″)<\/th>\n | 32 mm ID (≈1¼”)<\/th>\n | 40 mm ID (≈1½”)<\/th>\n | 50 mm ID (≈2″)<\/th>\n<\/tr>\n | \n| 6.0 mm — Cat5e UTP\/FTP<\/td>\n | 4<\/td>\n | 6<\/td>\n | 11<\/td>\n | 17<\/td>\n | 27<\/td>\n<\/tr>\n | \n| 6.2 mm — Cat5e SFTP, Cat6A UTP<\/td>\n | 4<\/td>\n | 6<\/td>\n | 10<\/td>\n | 16<\/td>\n | 26<\/td>\n<\/tr>\n | \n| 6.3 mm — DMX512 cable<\/td>\n | 4<\/td>\n | 6<\/td>\n | 10<\/td>\n | 16<\/td>\n | 25<\/td>\n<\/tr>\n | \n| 6.4 mm — Cat6A UTP<\/td>\n | 3<\/td>\n | 6<\/td>\n | 9<\/td>\n | 15<\/td>\n | 24<\/td>\n<\/tr>\n | \n| 7.2 mm — Cat6A UTP \/ FTP<\/td>\n | 3<\/td>\n | 4<\/td>\n | 7<\/td>\n | 12<\/td>\n | 19<\/td>\n<\/tr>\n | \n| 7.8 mm — Cat6A SFTP<\/td>\n | 2<\/td>\n | 4<\/td>\n | 6<\/td>\n | 10<\/td>\n | 16<\/td>\n<\/tr>\n | \n| 8.0 mm — Cat6A SFTP 10G<\/td>\n | 2<\/td>\n | 3<\/td>\n | 6<\/td>\n | 10<\/td>\n | 15<\/td>\n<\/tr>\n | \n| 8.3 mm — speaker 2×1.5 mm²<\/td>\n | 2<\/td>\n | 3<\/td>\n | 5<\/td>\n | 9<\/td>\n | 14<\/td>\n<\/tr>\n | \n| 9.8 mm — speaker 2×2.5 mm²<\/td>\n | 1<\/td>\n | 2<\/td>\n | 4<\/td>\n | 6<\/td>\n | 10<\/td>\n<\/tr>\n | \n| 11.0 mm — speaker 2×4.0 \/ 4×2.0 mm²<\/td>\n | 1<\/td>\n | 2<\/td>\n | 3<\/td>\n | 5<\/td>\n | 8<\/td>\n<\/tr>\n | \n| 12.5 mm — speaker 2×6.0 \/ 4×4.0 mm²<\/td>\n | 1<\/td>\n | 1<\/td>\n | 2<\/td>\n | 4<\/td>\n | 6<\/td>\n<\/tr>\n | \n| 14.0 mm — speaker 4×6.0 mm²<\/td>\n | 0<\/td>\n | 1<\/td>\n | 2<\/td>\n | 3<\/td>\n | 5<\/td>\n<\/tr>\n | \n| 16.5 mm — speaker 8×4.0 mm²<\/td>\n | 0<\/td>\n | 0<\/td>\n | 1<\/td>\n | 2<\/td>\n | 3<\/td>\n<\/tr>\n<\/table>\n A zero in that table is a design answer, not a rounding error: a 14 mm or 16.5 mm speaker cable will not pass through a 20 mm conduit at the reference fill at all. The eight-core speaker sizes are the ones that catch people out, because they are ordered for a loudspeaker run and specified after the conduit is already in the wall.<\/p>\n If a conduit already carries other services, add their areas to the sum before comparing. Mixed sizes are computed by total area, not by counting cables.<\/p>\n Flat and oval cable<\/h2>\nFlat zip constructions are published as two dimensions — for example 4.5 × 9 mm for a 2×1.5 mm² flat speaker cable, or 3.8 × 7.6 mm for 2×2.5 mm². The circumscribed circle of an oval is the larger dimension, so using the larger number overstates the area and understates the count, which is the safe direction for a conduit calculation.<\/p>\n Flat cable also twists as it is pulled, and a twisted flat cable occupies the circle of its diagonal rather than of its width. For a long pull, treat a flat cable as round with a diameter equal to its larger published dimension.<\/p>\n What to put in an enquiry<\/h2>\nA diameter question can usually be answered from published data in one reply. Five details make that possible:<\/p>\n \n- The model or the family, plus the cross-section and core count.<\/li>\n
- The overall outside diameter you have designed the conduit around, if the conduit is already fixed.<\/li>\n
- The conduit type and its internal diameter (or trade size), and how many other cables share it.<\/li>\n
- The pull length and the number of bends.<\/li>\n
- The environment: indoor trunking, underground duct, tray, or outdoor exposure.<\/li>\n<\/ul>\n
Where the run is a multicore snake, state the channel count and ask for the overall diameter, because the published 3.1 mm is the inner jacket — the construction and the counting logic for that family are covered in the 8-channel audio snake cable guide<\/a>. For the buying route itself, the audio cable for installers<\/a> page sets out what an installation enquiry needs, and the exact construction of any shielded network model is on its own product page, for example Cat6A SFTP<\/a>.<\/p>\nFAQ: cable outside diameter and conduit fill<\/h2>\nIs the outside diameter the same as the cable size?<\/h3>\nNo. Cable size usually means the conductor cross-section in mm² or AWG, which describes current capacity. The outside diameter is the finished jacket dimension, and it is the one that decides conduit fill, glands and clips.<\/p>\n How many Cat6A cables fit in a 25 mm conduit?<\/h3>\nAt a 40 % fill and a 25 mm internal diameter: six cables at 6.2–6.4 mm O.D., four at 7.2 mm, and four at 7.8 mm. Shielded Cat6A is larger than unshielded, so the shielded count is lower.<\/p>\n Can I use the inner jacket diameter for a snake cable?<\/h3>\nNo. The 3.1 mm published for the LBS multichannel range is the inner jacket of the bundle. Conduit, glands and pulling calculations need the overall outside diameter, which is quoted on request for that family.<\/p>\n Do the fill percentages apply to signal cable as well as power cable?<\/h3>\nThe percentages in NEC Chapter 9 Table 1 are written for conductors and cables in conduit and tubing, and they are the reference most installers use for low-voltage signal cable too. Local electrical codes take precedence, and a long pull or a run with bends needs a smaller fill than the table shows.<\/p>\n Why does a flat cable have two diameters?<\/h3>\nBecause a flat construction is oval. It is published as width × thickness, and for a conduit calculation the larger dimension is used as the diameter of an equivalent round cable, which is conservative.<\/p>\n | |