Put a mains-input power supply inside an electrical enclosure that prevents contact with hazardous terminals and secures every cable entry. Keep its required cooling path open, and separate mains wiring from output wiring according to the supply documentation and applicable equipment standard. Ferrules improve compatible terminal connections; they do not make exposed mains terminals safe.
The enclosure must accommodate the complete installation: supply, inlet, protection, bonding, terminal guards, wiring and service access. Choosing a box around the supply’s outside dimensions alone misses most of those requirements.
What the enclosure must make safe
A perforated metal power-supply cover is not necessarily a complete electrical enclosure. Its purpose may include mechanical protection and ventilation while leaving connection terminals accessible for installation.
Your outer enclosure must address several separate hazards:
- Contact with energized input terminals, inlet connections or damaged wiring.
- Cable movement that pulls conductors loose or exposes insulation to sharp edges.
- A fault that energizes accessible metal without an effective protective bonding path.
- Loss of required separation between mains circuits and accessible low-voltage circuits.
- Heat buildup caused by obstructed vents, unsuitable orientation or restricted airflow.
A plastic cap over the terminal strip may address only one of these hazards. A metal box may prevent casual contact but still lack cable restraint, bonding or adequate cooling.
Start with the supply’s installation instructions and dimensional drawing. Confirm its intended mounting method, orientation, terminal covers, protective-earth connection and required clearances. Check whether its approval depends on installation inside a larger enclosure.
The enclosure is part of the equipment’s safety design, not an accessory added after wiring is complete.
What ratings and approvals do not establish
Environmental ratings describe protection against specified environmental conditions. They do not establish that your mains wiring, output circuit or complete machine is safe.
For example, specifying NEMA 4X for washdown does not establish circuit separation or acceptable internal temperatures. Our enclosures have manufacturer ratings for the specified design and are not UL listed.
Likewise, an approved power supply does not automatically confer approval on the finished assembly. Its installation conditions still apply, including any required outer enclosure, protective devices, mounting restrictions and temperature limits.
The enclosure listing and panel approval guide explains the distinction between an enclosure and the complete electrical assembly. Establish the project’s approval requirements before choosing the enclosure.
Metal construction also does not prove that an assembly contains an internal fire. Material suitability, openings, component protection and abnormal-operation requirements depend on the applicable equipment standard. Do not substitute an improvised printed cover or household container for a documented enclosure design.
How to contain terminals and secure cable entry
The outer enclosure should prevent access to hazardous live parts during normal operation. Opening it for service introduces different requirements, including isolation, guarding and control of stored energy.
Locate the supply so its mains terminals cannot be reached through ventilation openings, unused cutouts or cable entries. Required access protection must be assessed using the applicable equipment standard, not a visual estimate of finger clearance.
Where the supply documentation calls for a terminal cover, include that cover in the layout. A cover must not press on conductors or obstruct the supply’s ventilation. Insulating tape is not a substitute for a durable terminal guard or enclosure.
Cable entry and the inlet assembly
A cord entry needs both suitable insulation protection and mechanical restraint. A plain hole, even with smooth edges, does not provide strain relief. Select a gland or cord grip for the actual cable diameter, jacket and installation environment.
A detachable inlet also needs space behind its mounting face. Include its terminals, connector insulation, retention features and conductor bending space in the drawing. A switch-and-fuse inlet assembly does not automatically enclose its rear connections.
Specify the supply voltage, current, protective-device requirements and intended isolation function before selecting the inlet assembly. Do not assume that a single-pole switch disconnects every hazardous conductor under every supply arrangement. Protective earth must not be switched or fused.
The cutout and cable-entry guide covers penetration planning. The cutout designer can place those openings once the actual component drawings and rear clearances are known.
Ferrules and terminal compatibility
Ferrules can contain stranded conductor ends when the terminal manufacturer permits them. They do not replace insulation, guarding, strain relief or correct conductor sizing.
Match the conductor preparation to the terminal instructions. Those instructions determine acceptable wire types, ferrules, strip length and tightening torque. Do not tin stranded wire with solder as a substitute for an approved termination method.
No bare copper should project beyond the intended termination area. Avoid placing multiple conductors in a terminal unless that terminal expressly permits the combination.
Where mains and low voltage must separate
A 24 V output label does not, by itself, establish safe isolation or a power-limited output. Confirm the supply’s documented output classification and the requirements of the equipment it powers.
Lay out the mains entry, protective devices and input terminals as a defined wiring zone. Route output wiring toward its own terminals or exit point without passing across exposed mains connections.
Separation can involve routing, insulation, barriers, terminal construction and physical spacing. The applicable equipment standard and component instructions determine which measures are required. There is no universal enclosure clearance that makes every mains-and-24 V installation acceptable.
Allow for a loose conductor as well as the normal installed arrangement. A barrier may be necessary where a detached mains conductor could reach an accessible output circuit. Cable ties alone do not establish the required insulation or separation.
Bond accessible metal parts as required, including the enclosure, supply chassis and removable parts that could become energized. Do not assume hinges or incidental mounting contact provide a suitable bonding connection. Keep neutral separate from protective earth within the equipment unless the documented system design requires a designated connection there.
Use the grounding and bonding guide for the protective fault path. For layouts containing additional distribution branches, the article on one power input for multiple devices addresses that separate design problem.
How to leave the cooling path intact
A supply intended for free-air operation may run too hot inside a second enclosure. Its perforations do not guarantee useful airflow once a nearby wall, wiring duct or barrier blocks them.
Record the permitted mounting orientation and every required clearance on the layout drawing. Check the space above convection outlets and around fan intake and discharge openings. Include terminal covers and wiring bundles when assessing those spaces.
An internal fan moves heat around the enclosure; it does not necessarily remove heat from it. A supply’s own fan also cannot compensate for an outer enclosure that lacks a suitable heat-rejection path.
Choose the enclosure’s environmental protection and thermal approach together. Adding ventilation later changes the opening design and can compromise the intended environmental protection. Ventilation openings must also preserve protection against contact with hazardous parts.
The article on power supply enclosure cooling and temperature checks covers heat assessment and operating-temperature verification. Use that assessment to establish dimensions rather than selecting a box solely because the supply fits inside.
What to check before energizing
Mains assembly and verification require qualified electrical work under the applicable equipment and installation standards. Disconnect all sources before internal work, control reconnection, and verify absence of voltage with suitable equipment. Follow the supply’s documented discharge precautions; disconnecting the cord does not prove that stored energy has dissipated.
Before release, the completed assembly needs checks appropriate to its construction and intended use:
- Confirm guards, covers and blanking devices prevent unintended access to hazardous parts.
- Verify cable restraint and ensure terminal connections carry no external cable pull.
- Inspect insulation, conductor preparation, terminal compatibility and specified tightening torque.
- Verify protective bonding using the applicable test method and acceptance criteria.
- Confirm required separation remains intact with the door closed and wiring secured.
- Check protection, supply compatibility, markings and the documented isolation arrangement.
- Verify operating temperatures with the enclosure closed under the specified worst-case operating conditions.
Any dielectric or insulation testing must follow the applicable assembly procedure and component limitations. Improvised test voltages can damage filters, surge-protection components or the supply itself.
What to put on the enclosure drawing
Specify a complete installation envelope, not just the power supply’s length and width. Depth must include standoffs, terminals, guards, wiring bends and clearance to the closed door.
The enclosure sizing guide covers dimensional planning. For a compact assembly with additional switching components, the article on housing a power supply and relay addresses that particular layout.
| Drawing or order item | Requirement to record |
|---|---|
| Installation environment | Indoor or outdoor location, dust, moisture, chemicals and ambient temperature range |
| Approval requirements | Applicable equipment standard, required evaluation and acceptance requirements |
| Enclosure construction | Material, dimensions, mounting arrangement and required environmental rating |
| Supply installation | Exact supply drawing, mounting orientation, fixing locations and documented clearances |
| Mains entry | Actual inlet or gland drawing, cable range, rear terminal space and strain relief |
| Terminal protection | Required covers, internal guards and access for isolated maintenance |
| Circuit separation | Mains and output wiring zones, required barriers and insulation provisions |
| Protective bonding | Enclosure, door and equipment bonding provisions required by the design |
| Thermal provisions | Required airflow paths, heat-rejection method and temperature-verification conditions |
| Other penetrations | Output connectors, operators, ventilation components and unused-opening closures |
We build custom enclosures with your specified material, width, height, depth and cutouts, starting at one piece. Supply the component drawings and layout requirements before the enclosure drawing is finalized.
Once those requirements are established, the enclosure selector can help identify a dimensional match or carry the requirements into a custom request. A dimensional match still needs electrical and thermal verification.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 30 × 24 × 10 in | 304 stainless | 30 x 24 x 10 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 6 × 6 × 4 in | 304 stainless | 6 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Do ferrules make exposed power supply terminals safe?
No. Ferrules can improve stranded-wire termination when the terminal manufacturer permits them, but they do not prevent contact with energized terminal hardware. The installation still needs suitable guarding, cable restraint, conductor preparation and an enclosure appropriate to the equipment and environment.
Is the power supply’s metal cover enough protection?
Not necessarily. A perforated cover may protect internal components while leaving input terminals accessible. Check whether the supply is intended for installation inside other equipment, and follow its requirements for terminal covers, mounting, protective bonding, clearances and the outer enclosure.
Can 24 V output wiring share space with mains wiring?
Not solely because the output is marked 24 V. Separation depends on the supply’s documented isolation, circuit classifications, wiring insulation and applicable equipment standard. Plan distinct wiring routes and determine whether physical barriers or additional insulation are required, including protection against a loose mains conductor.
Should the power supply use a catalog or custom enclosure?
Use a catalog enclosure only when its usable dimensions, construction and available penetrations meet the complete installation requirements. Custom construction becomes useful when terminal guards, barriers, inlet placement or cooling clearances cannot fit properly. Neither approach removes the need to verify the finished electrical assembly.
