Armoured fibre cable has a metal or dielectric layer under the outer jacket that resists rodents, crushing and impact. Corrugated steel tape suits direct burial and ducts, interlocking armour suits indoor routes without conduit, and steel wire suits heavy mechanical loads. Unarmoured cable is lighter, smaller and cheaper, and is adequate inside trays, conduit and protected ducts.
What armour adds to a fibre cable
An armoured fibre cable (armored fiber optic cable in US usage) has a protective layer between an inner jacket and the outer jacket. The armour resists rodent bites, crushing, impact and accidental contact with digging tools. In some routes it allows the cable to be installed without conduit or duct.
Armour does not usually carry the pulling load. Tensile strength comes from aramid yarn or a glass-reinforced plastic (GRP) central member, except in steel wire armoured designs. The price of armour is a larger diameter, more weight, a larger bend radius and, for metallic armour, the need to bond and earth it.
Unarmoured cable relies on its jacket, buffer and strength members alone. Inside a protected pathway that is enough, and its smaller size lets more cables fit in each tray or duct.
Armoured fibre cable types compared
| Armour | Construction | Strengths | Limits | Typical use |
|---|---|---|---|---|
| Corrugated steel tape | Thin steel tape, corrugated and wrapped lengthwise with an overlap, under a polyethylene jacket | Good rodent and crush resistance, acts as a moisture barrier, stays reasonably flexible | Metallic, must be bonded and earthed | Direct burial, ducts, outdoor routes |
| Interlocking armour | Aluminium or steel strip wound helically with interlocking edges, often with an outer jacket | High crush resistance, can replace conduit in some indoor routes | Bulky and heavy, dents if struck hard | Industrial plants, risers and routes where codes allow armoured cable without conduit |
| Steel wire armour | Galvanised steel wires laid helically around the core | Highest tensile and crush strength | Heavy and stiff | Direct burial in difficult ground, heavy industrial routes |
| Stainless steel spiral tube | Flexible spiral tube under the jacket, around the fibre and aramid | Crush and bite resistance at patch cord size | Less protection than tape or wire | Armoured patch cords, equipment links, some deployable cables |
| Dielectric (glass yarn or GRP rods) | Non-metallic layer of glass yarn or rods | No earthing needed, some rodent deterrence | Less bite protection than steel | Routes near power lines or in lightning-prone areas |
Rodent and pest protection
Rodents gnaw cable to wear down their teeth, and a single bite through to the fibre takes a link down. Corrugated steel tape is the most common defence for buried and ducted routes. Glass yarn armour gives partial protection and avoids metal, which suits sites where earthing is difficult. Squirrels are a known problem on aerial routes, and termites in some tropical regions, where a polyamide (nylon) outer sheath is sometimes added.
Repellent additives in jackets exist, but results vary, so treat them as a supplement to armour rather than a replacement. A sealed duct with no gaps at entry points also removes much of the risk.
Indoor, outdoor and fire performance
Outdoor cable uses a UV-stabilised polyethylene jacket, usually black, and water blocking with gel or dry swellable tapes. Indoor cable needs fire performance. Across Europe, India and the Gulf, buyers usually ask for low smoke zero halogen (LSZH) jackets tested to the IEC 60332 flame tests, IEC 61034 smoke density and IEC 60754 acid gas methods. In the EU, the Construction Products Regulation classes installed cables by reaction to fire under EN 50575.
In the United States, NEC Article 770 lists optical cable by type: OFNP, OFNR and OFN for nonconductive cable, and OFCP, OFCR and OFC for conductive cable. Metallic armour makes a cable conductive under that scheme, and the code requires metallic members to be bonded or earthed where the cable enters a building. Indoor/outdoor designs carry both an outdoor construction and an indoor fire rating, which avoids a transition splice at the building entry.
Bend radius, weight and handling
Armour adds diameter, and bend radius scales with diameter. A common rule in ANSI/TIA-568 for outside plant cable is a minimum bend radius of 10 times the outside diameter with no load and 20 times under pulling tension. Use the figure on the cable datasheet where it differs.
- Steel tape can buckle if bent below its minimum radius, and the fold then presses on the fibres.
- Interlocking armour can dent and stay deformed after an impact.
- Steel wire armour is heavy, so pulling tension, drum size and tray loading need checking before installation.
- Spiral steel tube on patch cords resists kinking, which is one reason armoured cords are used at equipment where cables get trodden on or caught in doors.
When unarmoured cable is enough
Most fibre inside buildings and data centres is unarmoured. Cable trays, conduit, innerduct and raised floors already give mechanical protection, and the smaller diameter matters when hundreds of links share a pathway. Unarmoured cable is also easier to strip and terminate. Choose armour indoors only where the route is exposed: plant rooms, factory floors, ceiling voids with rodent activity or runs through areas with machinery.
When tactical cable is the better answer
Armoured cable is designed to be installed once and left in place. Links that are laid out, recovered and laid out again treat armour badly. Steel tape and wire fatigue under repeated flexing, take a permanent set on reels and add weight that a crew has to carry.
Tactical cable takes a different route to protection. It uses tight-buffered fibres, a dense layer of aramid yarn and a tough polyurethane jacket, which together resist crushing and abrasion while staying flexible enough to wind onto a reel hundreds of times. Where vehicles or heavy equipment will cross the cable, a light stainless steel spiral can be added under a tactical jacket. Radix makes this kind of armoured tactical cable with LC, FC, SC or ST connectors. Our tactical fibre optic cable guide covers construction and reels in detail.
What to specify
- The route: direct burial, duct, tray, aerial, indoor exposed or temporary.
- Armour type, and whether metal is acceptable on that route.
- Fibre type and count, for example 12 fibres OS2.
- Jacket material and fire rating required by local code.
- Connectors or pre-termination, if the cable arrives as an assembly.
- Length per drum, and any marking or labelling.
Ask for crush, tensile and bend radius figures on the datasheet for the exact construction quoted. Radix supplies armoured fibre optic cables and outdoor fibre assemblies made to drawing; send the details through the quote form.
Questions buyers ask
Does armoured fibre cable need to be earthed?
Cable with metallic armour should be bonded and earthed according to local electrical code, typically where it enters a building. Dielectric armour made of glass yarn or GRP does not need earthing, which is why it is chosen near power lines and in lightning-prone areas.
Can armoured fibre cable be buried directly?
Cable designed for direct burial, usually with corrugated steel tape or steel wire armour and a polyethylene jacket, can be laid straight in a trench. Follow local rules for burial depth and use warning tape above the cable. Indoor armoured cable is not built for burial.
Is armoured cable stronger in tension than unarmoured cable?
Not necessarily. In most designs the pulling load is carried by aramid yarn or a GRP central member, not the armour. Steel wire armour is the main exception. Check the rated installation tension on the datasheet before pulling.
Do I need armoured cable in a data centre?
Usually not. Trays, conduit and raised floors protect the cable, and unarmoured cable is smaller and easier to manage. Armoured patch cords are sometimes used where cables cross walkways or sit in exposed equipment areas.
What is an armoured patch cord?
It is a patch cord with a flexible stainless steel spiral tube under the jacket. It keeps the size of a normal cord while resisting crushing and bites, and it is used at equipment in factories, plant rooms and field sites.
Can rodents chew through armoured fibre cable?
Steel tape and steel wire armour resist most rodent damage. Glass yarn armour deters some animals but gives less protection. Damage usually happens where armour has been stripped back at joints, so seal and protect those points as well.