Fiber or a wireless link between two buildings

The comparison

Distance and what is in between

For two buildings on the same property with 50 metres of grass between them, fiber is usually straightforward and worth doing. Trenching across grass is the cheapest kind of trenching.

For two buildings separated by a paved yard that trucks use, the calculation changes fast. Cutting and reinstating asphalt is expensive, and doing it across an active yard means shutting down part of your operation for the duration.

For buildings separated by land you do not own, or a road, fiber may be impossible regardless of budget. That is not an engineering problem, it is a permissions problem, and it can take months to discover the answer is no.

For distances beyond a few hundred metres on a rural property, the trenching cost scales linearly while the radio cost does not, and the radio wins on price by a wide margin.

What kills each option

Fiber gets killed by what is under the ground. Rock, existing services, a septic field, a high water table. You are also legally required to have utilities located before digging, and that process sometimes reveals that the direct route is unavailable and the practical route is twice as long.

Also: nobody has ever regretted installing conduit. If you are digging anyway, put in conduit larger than you need and pull spare fiber through it. The trench is the expensive part. Coming back to dig the same trench again because you ran exactly enough fiber is the avoidable mistake.

Wireless gets killed by line of sight, and people misjudge this. Being able to see the other building is not the same as having a clear path. A radio link needs clearance around the direct line, not just along it, because part of the signal travels slightly off-axis and obstructions near the path still interfere with it. This is why a link that clears a rooftop by a metre performs worse than one with several metres of clearance.

Trees are the specific problem. A link that works in March through bare branches degrades badly in June. Leaves contain water and water absorbs the frequencies these links use. This is the single most common cause of a wireless bridge that seemed fine at installation and became unreliable.

And future construction. A clear path today can be blocked by a building going up on the lot in between, and you have no say in that.

Throughput, and when it actually matters

A modern wireless bridge carries a lot of traffic. For an office needing file access, a shared printer, phones and internet, it is plentiful. Most businesses never approach the ceiling.

Where it matters:

Cameras. A dozen cameras in the outbuilding recording to a recorder in the main building is a continuous heavy load in one direction. This is the most common case where a bridge that seemed adequate turns out not to be.

Large file transfer. Design, video, imaging, anything where people move gigabytes routinely.

Server access. If applications in one building depend on a server in the other, latency and throughput both matter, and users notice.

Fiber’s real advantage on throughput is not today’s speed. It is that upgrading means changing the equipment at each end, not digging up the ground. A trench dug once carries whatever you want in twenty years.

The lightning point people get wrong

There is a common belief that fiber is dangerous between buildings and wireless is safe, or the reverse. The truth is that both are fine, and copper is the problem.

Running copper Ethernet between two buildings creates a conductive path between two separate electrical grounds. A nearby lightning strike induces a surge that travels along it and destroys equipment at both ends. This is a well-known failure and it happens regularly on rural properties.

Fiber is glass and carries no current, so it breaks that path entirely. A wireless bridge has no physical connection at all, which does the same thing.

So on this specific point, either choice is correct and copper is the one to avoid. If you have copper running between two buildings right now, that is worth changing regardless of which option you eventually pick.

Both still need proper grounding of the equipment at each end, and a bridge on a mast on a metal building needs it more than most.

The short answer

Under about 100 metres across ground you can dig: fiber. Put in conduit and spare strands while the trench is open.

Across a paved yard, a road, or land you do not own: wireless bridge, after checking the path clearance properly rather than eyeballing it.

Several hundred metres on rural land: wireless bridge on cost, unless the traffic is heavy or you have a specific reason to want permanence.

Trees anywhere near the path: fiber, or expect the link to degrade every summer.

Cameras in the far building recording to the near one: lean fiber, or size the radio link generously for the sustained load.

A temporary arrangement, or one you want working next week: wireless bridge. It can be installed in a day and it can be removed and reused elsewhere later.

Whichever you choose, get the copper out from between the buildings.