Fiber optic or copper for two buildings

This article was machine-translated from French and is being reviewed. Prices are in Algerian dinars excl. VAT.

Between two buildings more than 100 m apart, fiber optics is the normal solution: a copper cable (Cat6 or Cat6A) is limited to 100 m per link. Fiber optics in a company also electrically isolates the two buildings and ignores electromagnetic interference. It requires specific connections and tests, however. Here’s how to decide.

How far does Cat6 or Cat6A copper go?

The 100 m limit applies to a full channel: 90 m of cable laid (permanent link) plus 10 m of cords in total. Cat6 supports 1 Gb/s over this distance, Cat6A 10 Gb/s. Details are in the guide Cat6 or Cat6A.

Beyond 100 m the standard offers no guarantee. A link may work, but with errors or reduced throughput, unpredictably. Do not rely on it for a production site. Always measure the actual cable path (detours, rises, drops), not the straight‑line distance between buildings.

Between two buildings, length is not the only issue. Buildings may have different grounding. A copper cable then transmits potential differences and surges, especially lightning‑induced ones, to the equipment. The cable must be outdoor‑rated, UV and moisture resistant, and network ports protected by a surge protector. Optical fiber does not conduct electricity: it eliminates the risk of transmitting surges and potential differences between buildings.

Multimode or single‑mode fiber: differences

These ranges are from IEEE 802.3 with standard optics. More powerful optics exist for longer distances, e.g., 40 km at 10 Gb/s.

If an old multimode cabling exists, identify it before buying optics. OM1 fibers have a 62.5 µm core, OM2, OM3 and OM4 have a 50 µm core, and the 10 Gb/s ranges of OM1 and OM2 are much shorter than those of OM3 and OM4. Never mix types: a single‑mode fiber does not splice with a multimode fiber, and an optical module is designed for one or the other.

Connect the fiber to your network

Two methods exist to connect fiber to a copper network. In both cases, the fiber can terminate in a technical room of the second building, and copper then serves the offices up to 100 m.

SFP modules. Many switches have SFP ports, where you insert an optical module chosen for the fiber type and distance. It is the cleanest solution. In the store, the GENATA Switch 24 ports Gigabit PoE has two uplink SFP ports, rated up to 2.5 Gb/s in its designation, and the D-Link DGS-1210‑52MP has 4 combo ports. A combo port shares a slot between an RJ45 jack and an SFP socket: you use one or the other. The modules at both ends must be compatible: same fiber type, same speed, and same wavelength, except for bidirectional modules that work in complementary pairs.

Media converters. They convert the copper (RJ45) signal to optical, with a converter at each end of the link. The store offers two single‑mode SC simplex converters at 1310/1550 nm: the 20 km model at 100 Mb/s and the 3 km model at 1,000 Mb/s. Their designation mentions PoE: check the available power on the datasheet. The 20 km model does not exceed 100 Mb/s: do not choose it if you want Gigabit. These converters operate on a single fiber: one end emits at 1310 nm and receives at 1550 nm, the other does the reverse. The two converters of a link are therefore complementary models, often sold in pairs: check the datasheet if the item is sold individually or as a pair. The connector type (here SC) must be the same at both ends.

Fiber connectors are not crimped like an RJ45. You solder a pigtail to the fiber by fusion, or use a pre‑connectorized cord, then store the splices in a box. This work requires specific tools.

Lay, protect and test the link

• Type of cable. Choose a cable designed for the route: indoor, outdoor or buried. A buried cable requires protection against water and rodents, and is pulled through a conduit (sheath).
• Armored cable. The armor must be grounded. A fully dielectric cable avoids this constraint.
• Bending radius and cleanliness. Follow the manufacturer’s bending radius. Clean connector ends before each connection: dust can degrade the link.
• Reception test. Measure end‑to‑end loss with a light source and optical wattmeter, then use an OTDR to locate any faults. Keep the measurement report. It must stay within the loss budget allowed by the chosen optics, as indicated in their datasheet.
• Spare. Keep spare length at each end to allow a re‑connection.
• Routing and authorisations. If the route crosses a public way or third‑party land, find out the required authorisations before quoting.

When to choose fibre, when to stay with copper

Keep copper in these cases:

• the actual route is less than 90 m of cable;
• 1 Gb/s is sufficient, or 10 Gb/s on Cat6A;
• the link stays within one building, or between two rooms powered by the same electrical installation.

Switch to fibre in these cases:

• the actual route exceeds 90 m;
• the link connects two buildings, for electrical isolation and lightning protection;
• the environment is disturbed: motors, transformers, power cables;
• you anticipate speeds above 10 Gb/s or future growth;
• you connect more than two buildings: a fibre core network serves each building.

Particularities in Algiers

• Power outages. Fiber does not carry power: the switches and converters at both ends each need a supply. Without a UPS on each side, the link fails. See the guide UPS: how to choose power.
• Heat and sun. Use a UV‑resistant outdoor cable and place enclosures in shade or a ventilated room.
• Coastal humidity. Protect junction boxes with a waterproof enclosure.
• Earthworks. They can easily damage buried cable. Run fibre in a conduit, mark the route and keep photos and a plan before backfilling.

Frequently asked questions

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