Mounting a switching power supply in an enclosure

Short answer: enclosed switching supplies share no chassis size and no mounting pattern — each vendor draws its own box, with ATX desktop units and 1U rack supplies as the two fixed exceptions. So plan the mount around the parts that are standard: a 35 mm [1.4 in] DIN rail to EN 60715 for DIN-format bodies, a removable bracket for everything else, and 10 mm [0.4 in] of spare width per side so a replacement from another vendor lands on the same holes. Order the cutouts with the box, and the holes arrive made with the body; our boxes are delivered in 10 business days, counted from your approval of the drawing.

Are switching power supply chassis sizes standardized?

Mostly no: an enclosed switching supply is a vendor-specific box, and two makers' 480 W units rarely share a chassis or a hole pattern; the exceptions are ATX desktop supplies and 1U rack supplies, which follow fixed formats.

Width, depth, terminal positions and fixing holes are all vendor choices. A few vendors copy a rival's pattern on purpose to win retrofit swaps, but you cannot count on it across a catalog. Weight runs from a 620 g [1.4 lb] plastic-bodied DIN unit to a multi-kilogram ATX brick, so the mount, not the chassis, carries the load. Build for the swap: pick a mount that accepts the next supply, not only this one.

Which part of the mount follows a standard?

The rail is the standard part: a DIN-rail supply expects a 35 mm [1.4 in] top-hat rail to EN 60715 (the older EN 50022 drawing), in the 7.5 mm [0.3 in] or 15 mm [0.6 in] profile.

The body clips on with a foot at the back; the rail carries the standard. The common profile is 35 mm [1.4 in] wide and 7.5 mm [0.3 in] deep, and the 15 mm [0.6 in] deep version buys stand-off behind the body. Slotted rails carry their own fixing holes at 25 mm [1 in] spacing on the usual 1 m [39 in] length, so screw the rail down at those holes rather than a spacing you invent. The fundamentals live in the backplate and DIN rail layout guide, and the rail screws and end brackets are walked through in how to mount DIN rail on a backplate.

Which supplies come in a fixed size — ATX and 1U units?

Twice: an ATX supply follows its form factor, with a mounting face patterned at 150 mm [5.9 in] wide by 86 mm [3.4 in] high and typically four holes; 1U rack supplies converge on a couple of widths with blind-mate connectors.

ATX fixes the pattern because the supply bolts into a case full of pre-placed standoffs, and any ATX-branded unit lands on those four holes. Depth is the free dimension and it grows with wattage, so read the datasheet depth before you fix the enclosure depth. The 1U habit — fixed width, blind-mate connector, swap vendors without rewiring — is worth copying with a bracket even outside a rack. Where the output itself has to vary, as on a test rig or burn-in cart, the supply choice is its own question; selecting DIN rail programmable PSUs for test applications walks through it.

What do you need to mount a supply in the box?

You need the standardized part — a 35 mm [1.4 in] EN 60715 rail, or a 2-3 mm [0.08-0.12 in] aluminum or stainless bracket for sub-1 kg [2.2 lb] supplies — plus fixings, duct and factory cutouts.

• Top-hat rail, 35 mm [1.4 in] wide, 7.5 mm [0.3 in] or 15 mm [0.6 in] deep, cut to the backplate.
• For bracket builds: a 2-3 mm [0.08-0.12 in] plate with slotted mounting holes, flat or folded.
• Machine screws to suit the rail slots; for a stainless backplate, machine screws into clip nuts or clinch studs.
• Wiring duct, with the fill kept at the 50 % the duct makers' fill tables set (NFPA 79, section 13.5.2, Percentage Fills of Raceways).
• The supply datasheet: body width and depth, terminal screw torque, derating curve.

How do you mount a switching power supply step by step?

Decide the swap path first: a DIN-format supply clips to a 35 mm [1.4 in] rail in seconds, a bracket-mounted supply comes out with four screws, and both keep the wiring intact once you have ordered the spare width per side from the sizing section below.

1. Pull the numbers off the datasheet before anything else: body width, body depth, terminal screw size and torque, derating curve.
2. Set the mount. DIN-format body: rail. Odd chassis or ATX: a removable bracket; the removable mounting plate for bench wiring pulls the supply onto the bench with its wiring intact.
3. Screw the rail to the backplate at the rail's own holes, 25 mm [1 in] apart on the common slotted profile, with an end bracket at each rail end.
4. Position the supply with its spare width clear either side, input terminals toward the input duct, and clip or bolt it down to the datasheet torque — 0.5 Nm [4.4 lb-in] is the common figure on PSU screw terminals; the label wins.
5. Split the wiring runs: 120/240 V input from its gland straight to the input terminals, 24 V output to the load duct, nothing shared; the power supply enclosure safety for mains wiring article covers the separation and barriers.
6. Bond the body: a protective-earth conductor from the supply's PE terminal to the enclosure ground stud, contact surface cleared of paint, conductor sized from the overcurrent device ahead of it (NEC Table 250.122).
7. Isolate and lock off the input, verify absence of voltage, then land both runs and tug each conductor.
8. Measure the clear width at the body against your spare-width rule; that fit-check keeps the next vendor's box on the same mounting.

Step 6 is the grounding and bonding guide's territory: stud, keeper washer, cleared paint, and a conductor that matches the breaker ahead of it.

How much spare room should you leave around the supply?

Give the supply 10 mm [0.4 in] of spare width per side and take the depth from the datasheet; the worked example turns that into 170 mm [6.7 in] of clear width for an ATX-format unit.

The 10 mm figure is wiring slack and convection slack in one number: it takes a lug, a duct wall and the air path a convection-rated body expects. Height rarely decides anything — 86 mm [3.4 in] at an ATX face, or the body's own height on a DIN unit — but depth decides the box, because depth grows with wattage. Cut bracket holes as slots, not plain holes; a slot takes the pattern difference between this supply and the next one.

Worked example — bracket-mounting an ATX-format supply in a custom 304 stainless box. Inputs: mounting face 150 mm [5.9 in] wide (the ATX pattern); datasheet depth 140 mm [5.5 in] (example input — read yours off the label); 50 mm [2 in] behind the body for the loom and connector shells (example input); spare width per side as the rule above.

• Clear width: 150 mm + (2 × 10 mm) = 170 mm [6.7 in].
• Clear depth: 140 mm + 50 mm = 190 mm [7.5 in].
• In a 10 in [254 mm] wide custom body, the supply takes 170 mm and leaves 254 − 170 = 84 mm [3.3 in] of duct and rail run beside it.

Swap in your datasheet depth and your own loom allowance; the width rule stays. For a full row of DIN-rail parts, the minimum-depth arithmetic runs the same way, part by part, in the enclosure size for DIN rail devices: find the minimum depth article.

How do you check the mount before you close the door?

Run four checks: a tug test on the body and the rail screws, the spare-width gap clear each side, air at or under 40 C (104 F) beside the body after an hour at full load, and a door that closes on the gasket, not on a wire.

• Tug the body sideways and down; nothing shifts and no terminal turns.
• Measure the gap either side of the body against the spare-width rule from the sizing section, with clear air at the fan opening of a fan-cooled unit.
• Hold full load for an hour and read the air beside the supply: 40 C (104 F) or less; the power supply enclosure cooling and temperature checks article carries the wall-loss arithmetic for a sealed box.
• Close the door and look at the gasket all round: seated evenly, no wire under it.

Which mistakes cost you the rating or the supply?

The costly one is the field-drilled hole: once a supply bolts through a wall you drilled after delivery, the manufacturer rating — ours are rated NEMA 4X / IP66 by the manufacturer; not UL listed — no longer describes the box, because that hole was never sealed and tested.

• Drilling the wall on site. Put every hole on the drawing and let the factory cut them; the cutouts, glands and window openings guide shows what to dimension.
• Bolting the supply to the door. Door flex works every screw loose; the backplate carries it.
• Choking a fan. A fan-cooled unit needs the datasheet's clearance at its fan opening, and inside a sealed box that fan only stirs; a sealed box cools through the wall.
• Sharing one duct for mains in and 24 V out, filled past the tables' 50 %. Split the runs at the supply.
• Ordering before the drawing is settled. A made-to-order box takes 10 business days from your approval of the drawing, so read the supply datasheet first, then draw.

So the decision lands like this: DIN-format supply, 35 mm [1.4 in] EN 60715 rail; ATX or any odd chassis, a slotted removable bracket; either way the spare-width rule, separate input and output runs, and cutouts on the drawing. Start the box at the custom enclosure builder, or take a standard stainless body with your openings at the custom stainless cutouts page.

Catalog dimensions to compare

Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.

Questions