Datacenter
Data center cabinet and rack types and selection field guide
The two frame types and how to pick one: open-frame rack versus enclosed cabinet, the EIA-310 19 in standard, rack units and height, width, depth, load rating, airflow, PDU and rail mounting, and the spec that controls the call.
Direct answer
A data center rack holds and organizes IT gear on the EIA-310 19 in mounting standard and comes in two forms: an open-frame rack with bare posts and no doors, or an enclosed cabinet with doors and side panels. Gear depth, weight, density, and containment needs drive the choice, and the manufacturer's load and dimension ratings control it.
Key takeaways
- Data center racks come in two forms: open-frame racks with bare posts and no doors, or enclosed cabinets with doors and side panels.
- EIA-310 fixes the 19 in standard: 482.6 mm rail-to-rail mounting width and a rack unit (1U) of 1.75 in (44.45 mm).
- Standard cabinet width is 600 mm; 750 mm and 800 mm cabinets add side channels for cable managers and 0U PDUs.
- Match cabinet depth (roughly 1000, 1070, or 1200 mm) to the deepest device plus cable, PDUs, and slack, then confirm the rear door closes.
- Server door open area should be around 63 percent minimum for active loads; the rolling (dynamic) rating, not the static rating, governs moving a loaded cabinet.
What a rack and cabinet do, and the type split
A data center rack is the steel frame that holds IT equipment, and a cabinet is that frame wrapped in doors and side panels. Both mount gear to the same 19 in field, count height in rack units, and carry the power and cable for everything bolted into them. The difference that drives every other decision is whether the frame is open or enclosed.
Open-frame racks are bare uprights with no doors and no sides. Air and hands reach the gear from every direction, which is what telecom and network rooms want. Enclosed cabinets put doors on the front and rear and panels on the sides, which is what a data hall full of servers wants, because the box is what lets you control airflow, lock the gear away, and seal a cabinet into a contained aisle.
A rack is not just a place to set equipment. It fixes the airflow path, carries the power distribution, routes the cable, ties into the grounding system, and on a raised floor it sits on a coordinate that the power and cooling both reference. Pick the wrong frame and you fight all of that for the life of the room.
What is the difference between an open frame rack and a cabinet?
An open-frame rack is a frame of bare vertical posts with no doors and no side panels; a cabinet is the same mounting frame enclosed in doors, sides, and a top. The open frame gives you maximum access and unrestricted airflow for next to no money. The cabinet gives you security, dust and noise control, and the ability to direct front-to-rear airflow and seal into containment.
The split is not about quality. It is about what the gear needs. Patch panels, switches, and light network gear in a secured telecom room do fine on an open frame, and the open access speeds up the cabling work. Servers in a shared data hall need the enclosure, because that is the only way to keep one cabinet's hot exhaust out of the next cabinet's intake and to lock a tenant's gear away from the tenant beside it.
Use an open frame where access and cost win and the room handles security and air at the room level. Use a cabinet where the cabinet itself has to do that job. The rack readiness and white-space layout guide covers how the cabinet then gets placed, powered, and sealed once you have chosen it.
The EIA-310 19-inch mounting standard
The 19 in rack is the dimensional standard that lets gear from any vendor bolt into a frame from any other. In North America it is EIA-310, with IEC 60297 the international equivalent and DIN 41494 the older European one. The number everyone quotes is the 19 in width, but the standard fixes more than that. The rail-to-rail mounting width is 482.6 mm, and the mounting holes sit in a repeating pattern with a defined spacing so a 1U device lands on the same holes in any compliant rack.
Height is counted in rack units. One rack unit, written 1U or 1RU, is 1.75 in (44.45 mm), and every piece of rack-mount gear is sized in whole U. A 1U switch is 1.75 in tall, a 2U server is 3.5 in, and so on. The holes are grouped so each U has three holes, which is why fillers and rails line up the way they do.
What the standard does not fix is the cabinet's outside dimensions. The 19 in mounting width is the same in a 600 mm cabinet and an 800 mm cabinet. Width, depth, and U height are separate choices made outside the EIA-310 envelope, and that is the thing people conflate when they assume 19 in tells them how big the box is.
- 19 in rack
- The 482.6 mm rail-to-rail mounting width standardized in EIA-310 and IEC 60297
- U / RU
- Rack unit, the vertical mounting increment of 1.75 in (44.45 mm) on a 19 in rack
- Mounting hole pattern
- The repeating three-holes-per-U spacing that lets any compliant device land on the same holes
What is a rack unit (U) and how tall is a rack?
A rack unit, written U or RU, is the vertical measure of rack-mount space, equal to 1.75 in (44.45 mm) under EIA-310. Equipment height is given in whole rack units, so a 1U server occupies one of those slots and a 4U chassis occupies four. The count tells you how much gear a frame holds.
The classic cabinet is 42U, which is around 6 ft of usable mounting height in a standard footprint. Taller frames run 45U, 48U, and up to 52U, trading a higher cabinet for more slots over the same floor tile. The taller the cabinet, the more attention the ceiling height, the overhead tray, and the containment top have to get, which the rack readiness guide covers against the floor and ceiling budget.
Usable U is not the same as overall height. The overall cabinet height includes the base, the casters or feet, and the top frame, so a 42U cabinet stands well over 42 times 1.75 in. Plan to the usable U for the gear and to the overall height for the room, because the difference is what fouls a tight ceiling or a containment panel.
Two-post open racks for network and telecom
A two-post rack, also called a relay or telco rack, is two vertical uprights on a base, with gear mounted by its front ears or center-mounted on the posts. It is the cheapest frame in the room and the fastest to cable, because there is nothing in the way. It carries patch panels, switches, and light appliances in telecom rooms and network closets.
What it does not do is support deep, heavy gear. There are no rear posts, so a server on rails has nothing to land on at the back, and the load hangs off the front plane. Two-post racks are sized for the lighter loads they carry. A modern aluminum two-post might be rated on the order of 800 lb of equipment, but the rating is the manufacturer's, and a deep server simply does not belong on two posts no matter the number.
There is no airflow control on a two-post and no security. The frame is open on every side. That is a feature in a locked network room where you want the access, and a liability anywhere the gear needs containment or a locked door.
Four-post open racks for servers without doors
A four-post open rack adds a rear pair of uprights, so a server lands on rails front and rear the same way it would in a cabinet, but with no doors and no sides. You get rail-mount support for real server and storage weight while keeping the open access and the unrestricted airflow of an open frame. Static load ratings commonly run from around 1,000 lb up past 3,000 lb across product lines, but the figure is the manufacturer's and depends on the model.
The four-post open rack fits the room that handles airflow and security at the room level rather than the cabinet level. A dedicated, secured, well-contained server room can run open four-post racks and save the cost and the airflow restriction of doors. Hyperscale and lab spaces use them heavily for exactly that reason.
The trade-off is that you give up everything the enclosure does. No door means no per-cabinet lock, no front-to-rear airflow control, and no surface to seal into containment. In a shared or multi-tenant hall, that usually rules the open four-post out and sends you to the enclosed cabinet.
The enclosed cabinet, the data hall standard for servers
An enclosed cabinet is the four-post mounting frame wrapped in a front door, a rear door, side panels, and a top. It is the default for servers in a data hall because the enclosure is what makes everything else work. The doors and panels turn the cabinet into a duct that pulls cool air in the front and pushes hot air out the rear, instead of letting it swirl.
The enclosure does three jobs at once. It controls airflow, so the perforated front and rear doors set a clean front-to-rear path and blanking panels stop recirculation inside the box. It provides security, so each cabinet locks and a tenant's gear stays behind its own door. And it gives you a surface to seal, so the cabinet can bay to its neighbors and close into a hot-aisle or cold-aisle containment system.
A cabinet is also where depth, weight rating, perforation, and cable management all have to agree with the gear going in. The rack readiness guide covers placing, leveling, anchoring, powering, and sealing the cabinet once it is selected. This guide is about selecting it.
Rack and cabinet types at a glance
Five frame types cover almost every data center decision. The table lines each one up against what it is for and the one spec that decides whether it fits.
| Type | Best for | Key spec to check |
|---|---|---|
| Two-post open rack | Patch panels, switches, light telecom gear | Front-mount load rating; no rear support |
| Four-post open rack | Servers in a secured, contained room | Static load rating; rail depth |
| Enclosed cabinet | Servers in a shared data hall | Depth, perforation, lock, containment seals |
| Wide cabinet (750/800 mm) | High cable count and high density | Side-channel width for managers and 0U PDUs |
| OCP Open Rack | Hyperscale fleets on OCP hardware | 21 in bay, OpenU, DC bus bar, not 19 in |
What is the standard rack width?
The standard cabinet width is 600 mm, about 24 in, which matches the 600 mm floor tile on a raised floor so the cabinet lines up on the grid. The 19 in mounting field sits inside that width, leaving little room on the sides. For most server cabinets, 600 mm is the default and the tightest fit on the tile.
Wider cabinets run 750 mm and 800 mm, and the extra width is not for the gear. It is for everything beside the gear. A 750 mm or 800 mm cabinet opens up side channels for vertical cable managers and 0U PDUs, which is what high-density and heavily cabled cabinets need. The mounting field is still 19 in. The cabinet is wider so the cable and power have somewhere to live that is not in front of the airflow.
The catch is the floor grid. An 800 mm cabinet eats more of a two-tile cold-aisle pitch than a 600 mm one, so the wider box buys cable room at the cost of aisle and row math. Choose 600 mm unless the cable count or the density forces you wider, and then check what the width does to the row.
Cabinet depth and matching it to the gear
Depth is the dimension that gets a cabinet sent back. Cabinets run roughly 1000 mm, 1070 mm, and 1200 mm deep, with 1000 mm the common default and 1200 mm the extra-deep box for the longest gear. The depth has to swallow the deepest server plus the cable slack behind it plus the 0U PDUs in the rear channel, and still let the rear door close.
The mistake is buying to the server length alone. A 900 mm server in a 1000 mm cabinet looks fine on paper and fouls the rear door the moment the power cords, the cable arms, and the PDUs go in behind it. The working rule is to add the gear depth, the cabling and connector depth, and the PDU and slack room, then confirm the door still closes with everything in.
Deep storage arrays, large network chassis, and high-density compute push toward 1200 mm. Most general server work lives at 1000 mm to 1070 mm. Match the cabinet depth to the deepest device in the cabinet, not the average, because the one long chassis sets the requirement for the whole box.
How much weight can a server rack hold?
A server cabinet's load rating is set by the manufacturer, and the numbers are large. Enclosed server cabinets commonly carry static ratings on the order of 1,500 lb to 3,000 lb and higher, while two-post and lighter open frames carry much less. The number that matters is not one figure but three: the static rating, the dynamic or rolling rating, and the point load on the floor.
Static load is what the cabinet holds sitting still on its leveling feet. Dynamic, or rolling, load is what it can carry while it moves on its casters, and it is always the lower, more dangerous number, because a loaded cabinet rolling across an access floor funnels its whole mass through four small caster patches. The seismic rating is a separate question again, governed by the building code, not the cabinet vendor.
Read the rating as the manufacturer's, for that model, and check the cabinet's loaded weight against the floor's static, rolling, and concentrated ratings before it moves. The rack readiness and floor-load guide covers how those floor ratings are defined and verified, and why the rolling number is the one that cracks panels during the install.
Perforated doors, open area, and front-to-rear airflow
A server cabinet cools front to rear, and the doors are what make that work. The front and rear doors are perforated so cool air pulls through the front, across the gear, and out the rear. The number to ask for is the open area, the percentage of the door that is actually hole. Common guidance puts the minimum around 63 percent open for active server loads, with 80 percent perforated doors sold as the high-airflow option, and ANSI/BICSI 002 references a minimum open area for cabinets above a few kW per rack. Confirm the figure against the standard and the cabinet you are buying.
Too little open area chokes the airflow and starves the gear no matter how good the room's cooling is. A solid or glass front door on a server cabinet is a thermal mistake. It belongs on a network cabinet displaying gear, not on a loaded server box.
Open doors alone do not finish the job. Every empty rack space needs a blanking panel so hot rear air cannot loop back to the front intakes, and the cabinet has to be containment-ready so it can seal into the aisle. The rack readiness guide covers blanking, grommets, and containment in the placed cabinet.
Containment-ready and chimney cabinets
A containment-ready cabinet is built to seal into a hot-aisle or cold-aisle system rather than leak air around its edges. That means baying gaskets between cabinets, side and top seals, brush grommets on the cable openings, and a frame that closes against the aisle containment panels. A cabinet that is not containment-ready leaks at every gap, and the hot and cold air mix where you cannot see it.
The chimney, or ducted, cabinet is the self-contained version. It puts a duct on the top rear of the cabinet that captures the hot exhaust and runs it straight to the ceiling return plenum, so the cabinet contains its own heat without an aisle-wide containment build. Chimney cabinets fit rooms where you cannot contain a whole aisle, or where a few hot cabinets sit among cooler ones.
Either way, the cabinet has to seal as a unit. Brush grommets close the cable cutouts, blanking panels close the empty U, and the side and baying seals close the gaps between cabinets. The selection question is whether the cabinet you are buying supports the containment scheme the room is built around. The rack readiness guide covers the airflow sealing in detail.
Cable management and why the wider cabinet earns its width
Cable management is the job the wider cabinet exists for. Vertical cable managers, the fingers and ducts that run the full height of the side channels, route the patch and power cable up and down the cabinet without crossing the airflow path. Horizontal managers organize the cable at the panel. The wider 750 mm or 800 mm cabinet exists so those managers and the 0U PDUs have a side channel to live in.
A cabinet with no cable plan looks fine empty and chokes the day it is loaded. Cable dumped in the rear blocks the very airflow the perforated doors are trying to pull, traps heat against the gear, and turns the next move-add-change into a tracing exercise. The fix is planning the manager runs, the slack, and the path before the cabinet fills, not after.
This guide is about the cabinet that holds the cable. The structured cabling guide covers the copper and fiber plant itself, the pathways, the labeling, and the certification that the cabinet's patch field inherits. Choose the cabinet width and the manager hardware to the cable count the cabling design calls for.
PDU mounting and the 0U vertical strip
The rack PDU is the power strip the gear plugs into, and in a server cabinet it usually mounts vertically in the rear side channel as a 0U PDU. 0U means it takes no rack-unit space from the 19 in field. It lives in the channel beside the gear instead of eating a U. That is why the wider cabinet and the deeper cabinet matter, because the 0U PDU has to fit in the rear without fouling the gear or the door.
Most cabinets mount 0U PDUs with tool-less buttons or pins that snap into accessory rails in the channel, so a PDU goes in and comes out without hardware. Two PDUs, one each side, feed the A and B power the rack readiness guide covers, and mounting them in the channel keeps the cords out of the airflow.
The cabinet selection point is simple. Confirm the cabinet has the 0U mounting provisions and the depth for the PDUs you are running, on both sides, with the gear and cable already in. A cabinet that cannot fit its own power strips in the channel forces them into the rack space, and now the PDU is costing you U and blocking air.
Mounting rails: square-hole, round, and threaded
The mounting rails carry three kinds of hole, and the difference decides how gear bolts in. Square holes take cage nuts, the spring clips that snap into the hole and accept a screw, and square-hole rails are the current standard because the cage nut is replaceable and tool-less rail kits are built for them. Round holes are either threaded or take a clip; threaded round holes accept a screw directly. Threaded rails were common on older gear and strip out with repeated changes.
Square-hole with cage nuts won because it survives the move-add-change. A stripped thread on a threaded rail is a dead mounting point. A chewed cage nut pops out and gets replaced in seconds. Most server rail kits are designed for the square hole and click in tool-less, which is the whole point in a cabinet that gets re-geared over its life.
The selection check is to match the cabinet rails to the gear's rail kits. Confirm square-hole rails for modern tool-less server rails, keep a stock of cage nuts and screws for the gear that still needs them, and verify the rail depth adjusts to the actual device depth so the gear lands square front and rear.
Grounding and bonding the cabinet
Every cabinet has to be bonded to the data hall's grounding system, and it is not optional. The cabinet ties to the common bonding network with its own dedicated conductor so fault current has a low-impedance path back, the whole row sits at one potential, and the IT gear has the ESD reference it needs. Cabinets are never daisy-chained ground to ground down the row.
The bond has to bite bare metal. Paint and anodizing are insulators, so the connection uses a paint-piercing washer or a cleaned contact area at the bonding stud. A cabinet that looks grounded through its painted frame is not grounded.
Many cabinets ship with a grounding kit and bonding points built in, which is a selection feature worth confirming. The bonding detail, including the ANSI/TIA-607 common bonding network and the NEC power grounding that run in parallel, is covered in the rack readiness guide.
Security and locking in shared and colocation halls
In a multi-tenant or colocation hall, the cabinet door is the security boundary, so the lock is part of the spec, not an afterthought. Per-cabinet locks keep one tenant out of another's gear, and the better cabinets take electronic or smart locks that log who opened the door and when, which colocation contracts increasingly require.
The choices range from a simple keyed swing handle to combination, card, or networked locks with audit logging. The right level follows the deployment. An enterprise room behind a controlled door may only need a basic lock or none. A colocation cage with shared aisles needs per-cabinet locking and often the audit trail.
The selection point is to match the lock to the tenancy. Confirm the cabinet supports the lock type the contract or the security plan calls for, on both front and rear doors, because the rear door is the one people forget and it opens onto the same gear.
The OCP Open Rack alternative
The Open Compute Project's Open Rack is the hyperscale alternative to the 19 in EIA-310 rack, and it is a different standard, not a variant. Open Rack uses a wider 21 in (about 537 mm) equipment bay and a taller rack unit, the OpenU at 48 mm rather than the 44.45 mm U, which gives each slot more frontal area for airflow. The current generation is Open Rack v3.
The defining change is power. Instead of a PDU in each cabinet, Open Rack runs a vertical DC bus bar down the rack, and the gear blind-mates onto the bus bar when it slides in, so there are no individual power cords to each server. A power shelf feeds the bus bar. That architecture suits large, uniform, single-operator deployments where the whole fleet is built to the OCP spec.
Open Rack is not a drop-in for standard 19 in gear, and that is the point. It is a deliberate choice for hyperscale and large AI builds standardized on OCP hardware. For a mixed enterprise or colocation room running off-the-shelf 19 in servers, the EIA-310 cabinet is still the right frame.
High-density and AI cabinets
The fast-growing case is the high-density cabinet built for AI and GPU compute, and it is heavier, deeper, and far more power-hungry than a classic server cabinet. Where an older cabinet was planned around a few kW, an AI cabinet can draw well past 50 kW to over 100 kW, which changes the frame, the power, the cooling, and the weight all at once.
These cabinets tend to be deeper to hold long GPU chassis and the cabling, wider to carry the cable and power density, and rated for more weight because the gear is dense. Past roughly 30 kW to 50 kW, air alone stops being enough, so the high-density cabinet is built liquid-cooling-ready, with provisions for rear-door heat exchangers or direct-to-chip manifolds and the quick-disconnect plumbing that goes with them.
Selecting one means reading the weight, depth, power, and cooling requirements together, because they all move at once on a dense rack. The rack readiness guide covers the liquid-cooling readiness, the leak detection, and the floor-load reality of a cabinet this heavy. The structured cabling guide covers the fiber density an AI cabinet pulls.
Seismic frames and anchoring
In a seismic region, the cabinet has to be anchored, and the requirement comes from the building code, not the cabinet vendor. The International Building Code points to ASCE 7, and Chapter 13 holds the anchorage and bracing rules for nonstructural components like cabinets, scaled by the seismic design category, the cabinet weight, and the height of its center of gravity.
Some cabinets are sold as seismic-rated frames, built and tested to hold up and anchor in high seismic zones. Whether a given cabinet needs that frame, and how it anchors, is the engineer's call, and on a raised floor the anchorage runs through the floor to the structural slab, not into an access panel.
The selection point is to know the project's seismic requirement before buying the frame, because a standard cabinet may not be rated for a high seismic site. The rack readiness guide covers the anchoring detail and the floor connection. Build the anchorage the structural engineer specified and verify it against the adopted code edition.
How do I choose the right data center cabinet?
Start with the gear, then work outward to the room. The cabinet has to fit the deepest and heaviest device, so depth and weight rating come first, then the U count for how much gear it holds. From there the room drives the rest: the density sets the perforation and whether it has to be liquid-ready, the cable count sets the width, the containment scheme sets the sealing, the power sets the PDU provisions, and the tenancy sets the lock.
Two cabinets with the same 42U and 19 in field can be wrong for opposite reasons, one too shallow for the servers and one too narrow for the cable. The decision is not a single spec. It is matching the cabinet's depth, width, U, weight rating, perforation, containment, PDU mounting, rail type, and lock to the gear and the room together.
Budget comes last, not first, because the cheap cabinet that does not fit the gear or seal the aisle costs more than it saved the day it is loaded. Use the table to line the decision up against the deployment, and cross-check the placement, power, and sealing in the rack readiness guide.
| Selection driver | What it sets |
|---|---|
| Deepest device plus cable and PDU | Cabinet depth, 1000 to 1200 mm |
| Loaded weight, static and rolling | Load rating and the floor check |
| Power density per rack | Perforation, liquid-ready, PDU count |
| Cable count | Cabinet width and manager hardware |
| Containment scheme | Baying, side, and top seals, grommets |
| Tenancy | Per-cabinet lock and audit logging |
| U of gear | 42U, 45U, 48U, or 52U height |
Colocation, enterprise, and hyperscale cabinets
The deployment shapes the cabinet before any spec sheet does. A colocation cabinet is the most demanding on security and metering, because the hall is shared. It needs per-cabinet locking, often with audit logging, switched or metered PDUs so the operator can bill and watch the load, and tight containment sealing because the tenant next door shares the aisle.
The enterprise cabinet, in a room the owner controls end to end, can relax the per-cabinet security and lean on the room. It still needs the depth, perforation, and containment to cool the gear, but the lock and the metering can follow the owner's own policy rather than a tenant contract.
The hyperscale cabinet trends toward uniformity and scale. Large operators standardize on a single frame across thousands of cabinets, increasingly the OCP Open Rack with its DC bus bar, or a heavy high-density frame built for AI compute and liquid cooling. The choice is made once for the fleet, not cabinet by cabinet. Match the frame to which of these three rooms you are building, then refine the specs.
What to document
The cabinet selection is a record, not a memory, because the next person to add gear or move a rack reads it to know what the frame can take. Capture it per cabinet, keyed to the coordinate the rack readiness guide assigns, so the frame, its ratings, and its provisions are on file before the gear lands.
Record the cabinet type, model, and U height, the width and depth, the static and dynamic and seismic load ratings, the door perforation, the rail hole type and depth, the PDU mounting and count, and the lock and grounding provisions. The point is that a reviewer can confirm a piece of gear will fit and the floor will hold it from the record alone, without re-measuring the cabinet.
| Field to record | Why it matters |
|---|---|
| Cabinet type, model, and U height | Ties the frame to the gear it holds |
| Width and depth | Confirms gear, cable, and PDU fit with the door closed |
| Static, dynamic, and seismic load rating | Proves the cabinet and the move stayed inside the floor |
| Door perforation / open area | Documents the front-to-rear airflow path |
| Rail hole type and rail depth | Lets the next install match the gear's rail kits |
| PDU mounting and count | Confirms 0U power fits the channel, both sides |
| Lock type and grounding point | Records the security and the bond |
Common mistakes
- Buying a cabinet too shallow for the gear, so the rear door fouls on the servers, cables, and PDUs.
- Choosing 600 mm width where the cable count needs a wider side channel for managers and 0U PDUs.
- Reading the static load rating and ignoring the lower rolling rating that governs the move-in.
- Putting an open four-post rack where the hall needs containment and per-cabinet security.
- Specifying a solid or low-perforation door on a server cabinet and choking the front-to-rear airflow.
- Skipping cable management, so cable dumped in the rear blocks the airflow and traps heat.
- Mismatching the rail hole type to the gear's rail kits, or stripping threaded rails on repeated changes.
- Leaving empty U with no blanking panels, so hot exhaust recirculates inside the cabinet.
- Buying a standard frame for a seismic site that needs a rated, anchored cabinet.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
EIA-310 is the dimensional standard for the 19 in rack in North America, fixing the 482.6 mm mounting width, the hole pattern, and the 1.75 in (44.45 mm) rack unit. IEC 60297 is the international equivalent and DIN 41494 the older European one. These control how gear mounts; they do not set the cabinet's outside width, depth, or U count.
TIA-942 is the data center infrastructure standard that frames the cabinet environment, the row layout, and the cabling spaces the cabinet ties into. For airflow, ASHRAE TC 9.9 gives the thermal guidelines the perforation and containment are built to hold, and ANSI/BICSI 002 references cabinet open-area minimums for active loads. The OCP Open Rack base specification governs the 21 in OpenU rack and its DC bus bar as a separate standard.
The cabinet's load and seismic ratings are the manufacturer's, for the specific model, and the seismic anchorage follows the building code and ASCE 7 Chapter 13. Bonding follows ANSI/TIA-607 and the NEC, NFPA 70. Dimensions, open-area percentages, load ratings, and edition letters move between products and code cycles, so confirm them against the manufacturer's data and the adopted standard before citing a number on a submittal.
Units, terms, and conversions
Cabinet work mixes imperial and metric on one drawing, so the same dimension reads two ways. Rack height is counted in rack units, where 1U or 1RU is 1.75 in (44.45 mm), while width and depth are usually given in millimeters: 600, 750, or 800 mm wide and 1000 to 1200 mm deep. Weight ratings come in pounds or kilograms, where 1 kg is about 2.2 lb, and power density per cabinet is stated in kilowatts.
A few terms carry the subject. Open frame and cabinet are the two frame types. U or RU is the mounting increment. A 0U PDU is a power strip in the side channel that takes no U. The OpenU is the OCP Open Rack's taller unit on its 21 in bay. The terms below travel across the whole selection.
- U / RU
- Rack unit, 1.75 in (44.45 mm) of vertical mounting height on a 19 in EIA-310 rack
- 19 in rack
- The 482.6 mm rail-to-rail mounting width standardized in EIA-310 and IEC 60297
- Open frame vs cabinet
- A bare-post rack with no doors versus an enclosed box with doors and side panels
- 0U PDU
- Vertical rack power strip mounted in the side channel, taking no rack-unit space
- Cage nut
- Spring clip that snaps into a square rail hole to accept a mounting screw
- OpenU (OU)
- The OCP Open Rack unit, 48 mm, on the wider 21 in Open Rack bay
- Static vs dynamic load
- Weight a cabinet holds at rest versus while rolling on its casters, the lower number
FAQ
What is a rack unit (U)?
A rack unit, written U or RU, is the vertical mounting increment on a 19 in rack, equal to 1.75 in (44.45 mm) under EIA-310. Equipment height is given in whole U, so a 1U switch is 1.75 in tall and a 2U server is 3.5 in. A 42U cabinet holds 42 of those slots.
What is the difference between an open frame rack and a cabinet?
An open-frame rack is bare posts with no doors or sides, giving maximum access and airflow at low cost for telecom and network gear. A cabinet encloses the same frame in doors and panels, adding security, dust control, and front-to-rear airflow you can seal into containment. Servers in a shared hall need the cabinet.
What is the standard rack width?
The standard cabinet width is 600 mm, about 24 in, matching the raised-floor tile so the cabinet lines up on the grid. The 19 in mounting field sits inside that. Wider 750 mm and 800 mm cabinets add side channels for cable managers and 0U PDUs, for high cable counts and high density.
How much weight can a server rack hold?
A server cabinet's load rating is the manufacturer's, commonly a static rating of 1,500 lb to 3,000 lb or more for enclosed cabinets, less for two-post frames. The static rating is for sitting still; the lower dynamic or rolling rating governs moving it on casters. Check both against the floor's ratings before the cabinet moves.
How deep should a data center cabinet be?
Cabinet depth runs roughly 1000 mm, 1070 mm, and 1200 mm, with 1000 mm the common default and 1200 mm for the longest gear. Size to the deepest device plus cable, connectors, PDUs, and slack, then confirm the rear door closes. The long chassis sets the depth for the whole cabinet, not the average.
How many U is a standard server rack?
The classic server rack is 42U, about 6 ft of usable mounting height in a standard footprint. Taller frames run 45U, 48U, and up to 52U for more slots over the same floor tile. Usable U is less than overall height, which adds the base, feet, and top, so plan the ceiling to the overall height.
What perforation do server cabinet doors need?
Server cabinet doors are perforated for front-to-rear airflow, and the spec to confirm is the open area. Common guidance puts the minimum around 63 percent open for active server loads, with 80 percent doors sold as high-airflow. A solid or glass door on a server cabinet chokes the air; confirm the figure against the standard.
What is an OCP Open Rack and how is it different?
OCP Open Rack is the Open Compute Project's hyperscale standard, separate from the 19 in EIA-310 rack. It uses a wider 21 in bay, a taller 48 mm OpenU, and a vertical DC bus bar the gear blind-mates onto instead of individual power cords. It suits large OCP-standardized fleets, not mixed 19 in enterprise gear.
Square-hole or threaded rails: which should I use?
Square-hole rails with cage nuts are the current standard, because the cage nut is replaceable and most server rail kits click in tool-less. Threaded round-hole rails accept a screw directly but strip with repeated equipment changes. Match the cabinet rails to the gear's rail kits, and keep cage nuts and screws on hand for older gear.
When do I need a wider 800 mm cabinet?
Go wider than 600 mm when the cable count or the power density needs a side channel the standard width does not have. A 750 mm or 800 mm cabinet gives room for vertical cable managers and 0U PDUs beside the gear instead of in front of the airflow. The trade-off is more of the floor pitch per cabinet.
People also ask
Codes cited in this guide
This guide is written and reviewed against the published standards below. Always confirm the current adopted edition with the authority having jurisdiction.