Design guide 01

Five decisions, in the order they should be made.

A rack is chosen once and then lives through several generations of equipment. Decide in the order below, and the cabinet stops being the thing you replace first.

1 U height · 2 width · 3 depth · 4 load class · 5 mesh ratio and finish

42U = 2000 mm Standard external height

47U = 2200 mm External height with 5U of growth

1000 kg Static load, standard frame

Front view. External height 2000 mm over 42U. The mesh door is the only intake face, so the U ladder and the door are drawn at the same scale as the cabinet, not sketched.

The order

Decide these in sequence, not by importance.

1
Decision

U height

Decided by

the U you spend, plus the U you know you will add

If you decide it late

the row is full before the first server goes in
2
Decision

Width

Decided by

how cable is managed beside the rails

If you decide it late

cable runs in front of the intakes
3
Decision

Depth

Decided by

the deepest chassis plus the bend behind it

If you decide it late

the rear door will not close
4
Decision

Load class

Decided by

equipment, rails, PDUs and the person installing them

If you decide it late

the frame, not the door, is what fails
5
Decision

Mesh ratio and finish

Decided by

the airflow path and the room it sits in

If you decide it late

the door becomes the tightest point of the path

Rule Depth is the only one of the five you cannot change after the row is installed.

Question 01

42U, or 47U?

U height
U height	External height	Choose when
42U	2000 mm	Standard. Lowest cost per U; leaves headroom for trays and services above.
47U	2200 mm	You need 5U of growth, or 5U of patch, PDU and cable management you do not want to take out of 42U.
Other U counts	built to order	You are matching an existing row, or a fixed ceiling or plinth height.

Rule Count the U you spend, not the U you buy.

Question 01 · budget

Who is eating your U.

U budget. The bar is the full 42U; each band is a claim on it that is easy to leave out of the count.

Servers and storage
every chassis, at its rack height, not at its marketing height
Top-of-rack switches
1U or 2U each, and usually two of them
Patch panels
1U each, and the cable has to go somewhere
Horizontal PDU
1U or 2U if it is not mounted vertically
Cable management
1U to 3U per group of equipment
Shelves and KVM
the ones somebody will add without telling you
Blanking panels
every unused U
Reserve
the growth you already know about

Rule The rack is usually full before the first server is installed.

Question 02

600 or 800 wide?

Width
What it decides	600 mm	800 mm
Cabinet density in the row	more cabinets per running metre of row	fewer cabinets for the same row length
Vertical cable management	cable shares the side duct with the rails at full height	the extra 200 mm becomes a dedicated side channel
Side-mounted PDU	the PDU usually sits in the rear duct	a side-mounted PDU fits without taking U space

Rule Width is decided by how you manage cable, not by how much cable you have.

Question 03

1000, 1100 or 1200 deep?

Depth
Width × depth	Rail-to-rail room	What sits behind the rails	Choose when
600 × 1000	the tightest of the four	one shallow bundle, no vertical PDU behind the rails	the deepest chassis is short and the feed comes in from the top
600 × 1100	one step more than 1000	one bundle plus a vertical PDU	you need a PDU in the rear duct and a single cable bundle
600 × 1200	the usual choice for 19-inch servers with a rear cable bend	a full bundle bend, plus vertical PDUs on both sides	the deepest chassis has to keep its rail-to-front-panel depth with the bend behind it
800 × 1200	the same depth as 600 × 1200, with a wider body	a full bundle bend, with the cable moved out to the side channel	you manage cable in the side channel instead of the rear duct

Rule Measure the deepest chassis rail-to-front-panel, then add the bend of the thickest bundle behind it.

Dimensions

Every dimension on one sheet.

Front view: U ladder and external height · side view: depth, door swing and cable bend behind the rails · top view: width, uprights and mounting hole positions

. Solid = fixed in the order; dashed = hidden or a trajectory; blue = the two dimensions that are decided by everything on the other side of them.

Question 04

What the static load counts, and what it does not.

Counts toward static load

Installed items
The weight of every installed item.
Rails and shelves
Rails, shelves and cable management.
Vertical PDUs
Vertical PDUs and their fixings.
Installation load
The person leaning on the rails during installation.

Does not count

Lifting rating
It is not a lifting or transport rating.
Dynamic rating
It is not a dynamic rating.
Seismic rating
It is not a seismic rating.

1000 kg static load, standard frame

1500 kg on reinforced-frame models

IT cabinet load test report — 3 pages

Rule The static load is what the frame carries standing still. Say which frame you are quoting before you quote the number.

Question 05

Why the front door and the rear door do not carry the same number.

≥75% Front door mesh ratio

≥60% Rear door mesh ratio

Mesh ratio
Door	Ratio	What it does	Why the number	How it is checked
Front door	≥75%	the intake face for the whole cabinet	nothing else in the path is as cheap to get right or as easy to get wrong	light behind the door, measured open area, documented at handover
Rear door	≥60%	the exhaust face, shared with cable egress	cable openings take area away from the mesh that remains	same method, and a look at what has been run through the openings

The front door is the single intake face for everything in the cabinet, so it is the one surface where the open area is the whole specification. The rear door carries exhaust and cable egress at the same time, and the openings the cables leave through cannot be mesh. Checked on site with a light behind the door and a measured open area, not by eye.

Rule Do not accept a front door below 75% because the sample looked fine.

Discipline

An open U is a hole in the airflow path.

01
Close every unused U with a 1U blanking panel.
02
A server that does not fill its own U still leaves a gap above it.
03
Seal the gaps between adjacent equipment, not just the empty U.
04
A blanking panel is a panel, not a shelf.
05
Order blanks with the cabinets: they are the cheapest part of the airflow path.

Doors

A moving part has to keep three things at once.

Door type
Door	What it does	What to check
Perforated mesh door	Lets the airflow through and keeps the rack visible	Mesh ratio, flatness over the full height, and the bond
Solid door	Keeps dust and hands out, at the cost of the airflow path	Whether the equipment behind it can breathe at all

Front door, rear door and frame bonded at multiple points

Rule A door is a moving part: it has to keep its flatness, its mesh and its bond at the same time.

Sheet metal

2.0 and 1.2 mm each govern something different.

Gauge
Part	Material	What it governs
Uprights, 2.0 mm	SPCC cold-rolled steel sheet	The load path, and whether the mounting holes stay where they were punched
Doors, 1.2 mm	SPCC cold-rolled steel sheet	Flatness over a two-metre span, and the shape of the perforation

SPCC cold-rolled steel sheet from Baosteel / Anshan Steel

Finish

The finish steps, and what each one protects.

01Degrease
02Phosphate
03Electrostatic powder coat

Airflow
The coating does not enter the airflow path; it stays on the steel, and the mesh is punched before coating so the perforation edge is covered too.
Colour
Colour is held batch to batch by the powder supplier's reference, not by eye.
Cut edges
Phosphating covers the cut edge before the powder goes on, which is where a single-coat finish fails first.

Rule Say on the purchase order if a second batch has to match the colour of the first.

Self-check

Errors to look for in your own specification.

Common errors
Error	What happens
Choosing 42U from the U you buy	The row is full before the first server is installed.
Choosing depth from the room, not the equipment	The rear door will not close with the cable bend in place.
Accepting a front door below 75%	The door becomes the tightest point in the airflow path.
Quoting 1500 kg without naming the frame	1500 kg on reinforced-frame models only — the standard frame is rated 1000 kg.
Treating static load as a lifting rating	The cabinet is judged against a duty it was never specified for.
Reordering without naming the drawing set	The second batch does not match the first.

Specification block

Copy this into your technical requirement.

Rack, 19 in, 47U, 2200 mm external height
Width x depth: 600 x 1200 mm
Uprights: 2.0 mm SPCC cold-rolled steel; doors: 1.2 mm
Static load: 1000 kg (1500 kg on reinforced-frame models)
Front door mesh: >= 75%; rear door mesh: >= 60%
Grounding: front door, rear door and frame bonded at multiple points
Finish: degrease, phosphate, electrostatic powder coat

Copy this block into your technical requirement; the drawing set matches it line for line.

Send us the equipment list and the floor plan. We answer with a specification sheet and a drawing set.

Request the specification sheet

Next: Airflow & Cooling Power & Grounding