Will it fit,
and can you power it?

It is set by the circuit, not by the rack. In the UK a 32 A single-phase 230 V feed is 7.36 kVA nameplate, and BS 7671 lets you use all of it — at 0.95 power factor that is about 6.99 kW per feed. A 32 A three-phase 400 V feed is 22.2 kVA. With A/B redundancy the usable IT load is one feed's capacity, because either must carry the whole rack when the other fails. For context, Uptime Institute's 2025 survey puts the average of modal rack densities at around 9 kW, and more than 80% of operators have no racks above 30 kW — so a 20 kW rack is unusual and a 40 kW rack needs containment or liquid cooling and a room that can genuinely deliver it.

No — and this is the single most common error in UK rack design. The 80% continuous-load factor comes from the US National Electrical Code, which requires circuits to be sized at 125% of the continuous load; 80% is simply 1 ÷ 1.25. BS 7671 contains no equivalent rule. It requires only that design current ≤ device rating ≤ cable capacity, and that the fusing factor condition holds, and BS EN 60898-1 MCBs are calibrated to carry 100% of their rating continuously. The clearest proof is a single product sold under both conventions: APC lists one PDU as "22.1kW 400V 32A or 17.3kW 415V 30A" — identical hardware, two regional readings. NVIDIA's DGX SuperPOD design guide publishes an explicit breaker-derating column: 100% for IEC, 80% for NEC.

Ambient temperature. MCB trip current falls as the enclosure gets hotter — a 16 A device is good for 16.0 A at 30 °C but around 12.2 A at 60 °C. That is a genuine physical derating with a published curve, and the planner applies it when you raise the ambient above 30 °C. It is quite different from a flat 80% factor: it reflects the actual conditions in your comms room rather than a rule imported from another country's wiring code. Grouping factors and BS EN 61439-3 rated diversity are separate again — diversity is a simultaneity assumption about how many circuits run at once, not a continuous derate on each one.

The same as its IT load, in kW. Essentially all the electrical energy entering a rack leaves it as heat, so an 8 kW rack produces 8 kW of heat — 27,297 BTU/hr, or about 2.27 refrigeration tons. There is no 1.3× uplift at the rack. Uplift factors apply at plant level, where UPS losses, distribution losses and the cooling plant's own consumption are counted (that is what PUE measures), and applying them at both levels double-counts. The one addition worth making at the rack is UPS self-heat if the UPS lives in the same cabinet, which this planner adds to cooling but keeps out of the IT load.

It depends on the cabinet and on whether it is standing still. An APC NetShelter SX AR3300 is rated 1700.97 kg static but 1020.58 kg dynamic — the lower figure is what you may roll it at when populated, and a transport rating is lower again. Open four-post frames cap out around 907 kg and adding a centre rail does not raise that. Individual boxes matter too: over about 34 kg you need enhanced slide rails, at 54.9 kg you are into mechanical-lift territory, and at 90.7 kg a heavy-component support kit is specified. The planner flags each of these per item, because they apply to the box being lifted, not to the rack total.

A loaded rack puts its entire mass onto four small feet, so the load on the floor is highly concentrated. Point load is gross weight (equipment plus the rack's own tare) divided by the number of support points, expressed in kN. On a raised access floor this is the number that matters, and the trap is that BS EN 12825 floor classes are ultimate loads: you divide by a safety factor of 2 or 3 to get the working load before comparing. A rack that looks fine against the class figure can be well past the working load. Where the point load is too high, a spreader plate distributes it — but that is a design decision to make before the rack arrives, not after.

Not upright. A 42U cabinet is 1991–2006 mm tall externally and the standard internal door height is 1981 mm in England and Wales, 2040 mm in Scotland. The rack goes in on its side, or it is built in place from a flat-pack. Two related traps: the door leaf height is not the structural opening height, so measure the actual opening; and lift dimensions, corridor turning circles and floor loading en route matter as much as the door. The planner flags the doorway check automatically because it is the constraint most often discovered on delivery day.

Exactly 44.45 mm (1.75 inches), from EIA-310 / IEC 60297 — the universal hole spacing of 0.625 in, 0.625 in and 0.500 in sums to 1.75 in per U. Every calculation here uses 44.45 mm rather than a rounded 44 or 45 mm, because over 42U the rounding error is more than a full U. Note also that 0U equipment such as vertical rack PDUs consumes no mounting U but does take roughly 46–51 mm of rear channel depth, which competes with deep chassis for the same space.