Rack units, and the half of the space nobody counts
A rack unit is 1.75 inches of mounting height, and equipment is described in whole or half units. Adding up the units of the devices you intend to buy gives a number that is always too small, because a working panel is not a stack of devices touching each other. Between and around them goes the thing that makes the installation serviceable: somewhere for the cable slack to loop.
The habit of allowing a unit of management for every unit of patch panel looks wasteful on paper and pays for itself the first time somebody has to move a drop. Without it, the terminations are pulled tight into the back of the jacks, every change stresses the ones either side, and the bundle behind the panel becomes a solid mass that cannot be traced. With it, each cable has slack to be pulled forward and worked on. The cost is height in a box; the alternative cost is measured in hours and in jacks that fail six months later.
Depth is the constraint, not height
Wall enclosures are chosen for the height because that is the dimension on the product page. The dimension that decides whether the installation is any good is the depth, and it is fixed by the stud bay before anyone starts choosing.
The arithmetic is unforgiving. A device that is nine inches deep in a four inch cavity does not fit, and no amount of care changes that. Even when the device fits, the cable behind it has to turn through ninety degrees to reach it, and that turn has a minimum radius set by the cable specification. A patch cord forced into a tighter bend than its rating is degraded at the moment of installation, and the failure is a slow link rather than a dead one, which is far harder to diagnose. Depth needed is the deepest device plus room for the cable to turn, and if the enclosure cannot provide it the equipment belongs somewhere else.
| Constraint | How it usually shows up | Whether it can be worked around |
|---|---|---|
| Height | Runs out on the last device | Sometimes — move something out |
| Depth | Door will not close, or cords are crushed | Rarely — the cavity is the cavity |
| Heat | Equipment runs hot with the door shut | Vent, fan, or relocate |
| Power | No receptacle inside the box | Licensed work, plan it before the wall closes |
Why a closed can gets hot and what the density figure means
Everything electrical in the enclosure converts essentially all of its input power to heat. A sealed box has no airflow of its own, so it warms up until its surface sheds that many watts to the room, and the equipment inside sits at whatever temperature that turns out to be. Watts per cubic foot is a crude screening figure but a useful one, because it captures the thing that varies most between installations: the same equipment in a large open rack and in a small wall can are not the same thermal situation at all.
Treat a high density as a prompt to measure rather than as a verdict. Put a thermometer in the box, shut the door, come back in an hour, and compare against what the equipment documentation says it tolerates. If it is hot, the options in ascending order of effort are a vented door, a small fan drawing from the room, moving the powered devices out and leaving only passive terminations in the wall, or accepting a shorter equipment life. Sizing an actual fan is an airflow calculation rather than a density one, and the AV rack power and heat calculator does that arithmetic.
Power fed down the cable is somebody else budget
When the switch powers access points and cameras over the same cable that carries their data, the power leaves the enclosure and mostly becomes heat at the far end, in the device. What stays behind is the conversion and distribution loss, which is real but is a fraction of the delivered figure. That is why this page counts only a share of it in the enclosure and points the full budgeting question elsewhere. The number that matters at the switch is whether the sum of connected devices exceeds what the switch can supply, and what it does when they do, which the PoE power budget calculator works through.
Deciding the enclosure before the wall closes
Everything on this page is cheap to change while the framing is open and expensive afterwards. That includes the two items people most often defer: whether there is a receptacle inside the enclosure, which is licensed electrical work and needs to be planned rather than improvised, and whether the pathways into the box are large enough for the cables that arrive later. The low-voltage pathway fill calculator sizes those, and the ethernet drop calculator settles how many cables are converging on this point in the first place. Work out the panel last and you will size it for the drops you remembered; work it out first and the drop count, the pathway sizes and the enclosure all come out of the same list.
Questions people ask
How big should a structured wiring enclosure be?
Big enough for the equipment plus the management space plus a spare allowance, and deep enough for the deepest device plus the cable bend behind it. The height is the number people size on and the depth is the number that catches them out, because the cavity depth is decided by the framing before anyone chooses a box. Run the list before choosing rather than after, and if the answer is that the equipment does not fit a wall can, take that as information rather than as a problem to squeeze past. A small open rack in a cupboard or a utility space is easier to work in, easier to cool and easier to extend than any recessed enclosure.
How much spare capacity should I leave?
Enough for the device that arrives after the wall is closed, which in practice means at least a quarter and often more. The things that show up later are predictable in kind if not in detail: a second switch when the port count runs out, a backup supply after the first outage, a controller for something, and a shelf for the box with no mounting ears. The cheapest spare capacity is height in an enclosure you have not bought yet. The most expensive is the same capacity added by replacing an enclosure that is already terminated, which means unterminating everything.
Can I put the network switch in a wall enclosure?
Physically usually yes, thermally often unwisely. A switch is the largest continuous heat source in most home network installations and a sealed wall can is the worst place to put a continuous heat source. The watt density figure on this page is the screening test, and the definitive test is a thermometer in the box with the door shut for an hour on a warm day. If it runs hot the equipment will not necessarily fail immediately, it will age faster and behave oddly under load, which is a worse failure mode than an obvious one. Vented doors and fan kits exist for exactly this reason and are worth their cost.
Do I need a receptacle inside the enclosure?
If anything in it is powered, yes, and running one is licensed electrical work. This is the item most often left until after the wall is closed, at which point it becomes an extension lead trailing into a hole, which is both untidy and the sort of thing an inspection notices. Whether mains and low voltage may share the enclosure at all, and under what conditions, is decided by the code adopted where you are and by the authority having jurisdiction. Plan it with the electrician who is already on the job rather than resolving it from a web page.
What is the point of a patch panel when I could just plug the cables into the switch?
The panel exists so that the solid cable in the walls is terminated once and never moved again. Solid conductor cable is not designed to be flexed repeatedly; every time a run is unplugged and moved, the termination takes the strain. With a panel, the wall cable is terminated permanently on the back and all the plugging and unplugging happens with flexible patch cords on the front, which are cheap and replaceable. The secondary benefit is that a labelled panel is a map of the building, and the person who needs that map in five years will not be you.