Performance indicators for an indoor optical cable
As the telecommunications market offers a plethora of optical cables at very attractive prices, it is important to recall that not all cabling solutions are equivalent. Indeed, to ensure futureproof fiber optic installations and an optimal level of performance, several quality standards must be checked. First of all, when selecting an indoor FO cable it is important to make sure that:
- the selected product comes with a Declaration of Performance established by the manufacturer
- the CE marking is clearly affixed to the chosen cable
- that the body involved in the certification process is clearly indicated on the product’s label.
These three criteria combined are your guarantee that the selected indoor optical cable complies with all applicable European regulations, such as RoHS, for instance.
Which flame retardant cable for an indoor FTTH deployment ?
The fire behavior of the optical drop is fundamental for all indoor deployments. Indeed, just like power and control cables, communications cables are subject to the CPR (Construction Products Regulation) and the associated requirements to this framework. Depending on the materials used in the construction of their sheaths, communication optical cables offer different performances in case of a fire. Thus, to ensure the utmost security for users and equipment, before releasing a cable onto the market, three criteria are carefully examined:
- Fire behavior
- Resistance to fire
- The emission of dangerous substances.
Depending on the observed performances in relation with their thermal potential, fibre optic drop cables are classified into 7 Euroclasses, defined by the standard EN 13501-06 :
| Contribution to fire spread | Application | Euroclasses | Criteria for classification |
|---|---|---|---|
| Public transportation (plane, train, underground, etc.), crowded public places | Aca | Calorific value | |
| B1ca | Heat release + vertical flame spread + flame spread | ||
| B2ca | |||
| Road tunnels, high risk premises, hotels | Cca | ||
| Single dwelling units (SDUs), establisments open to the public | Dca | ||
| MDUs, SDUs | Eca | Flame spread |
According to a Sycabel* communication, a cable classified as Eca is 5 to 10 times more conductive to fire than a cable classified as Cca . This is why it is extremely important to make sure that the optical indoor drop cable of your choice is well suited to your deployment needs so to ensure safe and reliable FTTH infrastructures. Three additional criteria allow a more accurate cable classification for Euroclasses comprises between B1ca and Dca . These criteria are focusing on the fire behaviour of the cables in relation with the opacity of the emitted smoke, the presence of droplets ans the acidity of the smoke.
| Criteria | Level | Remarks | Consequences |
|---|---|---|---|
| Smoke | s1,s1a,s1b | Guranteed visibility ˃ 10m | Easy evacuation and intervention of the emergency services |
| s2 | General visibility ˂ 10m | Slower evacuation | |
| s3 | No or low visibility | Increased hazard | |
| Droplets and inflamed particles | d0 | No droplets | No secondary outbreak of fire |
| d1 | Persistence ≤ 10 s | Possibility of secondary fire outbreak, risk to persons | |
| d2 | Persistence ˃ 10 s | Important risk | |
| Smoke acidity | a1 | Low-acid and non-corrosive gas and smoke | Easy evacuation, no suffocation, no corrosion of materials |
| a2 | Low-acid but corrosive gas and smoke | Easy evacuation but corrosion of materials | |
| a3 | Acid and corrosive gas and smoke | Risk to persons and equipment |
Source : *Sycabel (French Professional Association of Manufacturers of Power and Communication Wires and Cables).
How to pick an indoor cable suitable to your network configuration ?
Depending on the network architecture, bringing the optical signal to the subscriber’s premises requires the use of one or several FTTH indoor cables. For instance, in urban areas, for connecting a subscriber residing in a multiple dwelling unit to the ultrafast broadband networks, telecom technicians will need a riser cable and an indoor optical drop in order to bring the optical signal from a BEP (Building Entry Point) to the room where the OTO (Optical Telecommunications Outlet) is mounted. The riser cable will thus be connected at the BEP level to the distribution cable that hauls the optical signal from the outside plant into the building. The same riser will be then used to bring fiber to each floor, thanks to its micromodule construction. Then, at each building’s level, a Floor Distribution Box (FDB) will be used so to connect the fiber from the riser cable to a flexible optical cable. This last one enables an easy and discreet routing of the optical signal up to the OTO, particularly around windows and doors or alongside baseboards.
For the connection of subscribers residing in SDUs or low dense areas to the ultrafast broadband networks, an indoor drop is enough for to make the connection between the Optical Telecommunications Outlet DTIo type (with the shape of a circuit breaker) installed inside a residential communication gateway and the OTO used as the end point of the FTTH infrastructure. As a general rule, for the same optical performances, it is advisable to choose the small diameter optical cable. To detail this recommendation, let’s take the example of the Droptic® LM1 and LM1L indoor drops. While the first one is designed with a diameter of 3.3mm, the second one presents an outer diameter of only 2.8mm. Thanks to this difference of 0.5mm between the two constructions, the LM1L is able to provide for superior static bending and kink performances, namely 12.5mm and 5mm vs. 15mm and 10mm for LM1. Thus, the LM1L drop cable is an ideal solution for almost invisible installations, while the LM1 drop is recommended for cable laying requiring superior maximum allowable tensions (150N thanks to the FRP rods included in its construction against 100N for the LM1 optical drop).