Use an internal distribution assembly intended for the installation, together with a correctly rated, externally operated supply disconnect. A plug-in power strip can be suitable only when its instructions permit the mounting, environment and supply connection. Cutting off its plug does not establish that the modified assembly remains covered by its original approval. For a metal enclosure containing mains wiring, specify protective-earth bonding, guarded terminals and coordinated overcurrent protection. Choose these parts before finalizing the enclosure dimensions or connector cutouts.
What the internal environment allows
Start with conditions inside the closed enclosure, not just conditions in the room. Internal temperature can exceed ambient temperature, particularly beside power supplies or equipment with ventilation openings.
Check the distribution assembly's instructions for enclosed installation, mounting orientation, ambient temperature and required clearances. A strip intended for accessible indoor use is not automatically suitable behind a closed equipment door.
For each installation, establish:
- Whether water, conductive dust, oil or cleaning chemicals can reach the enclosure.
- The maximum external ambient temperature and expected internal temperature.
- Whether condensation can occur during shutdown or overnight cooling.
- Whether vibration can loosen plugs, terminals or mounting hardware.
- Whether routine access requires opening the enclosure while other equipment remains energized.
An enclosure protects its contents from the specified external environment. It does not make an unsuitable internal component suitable for heat, moisture or vibration.
Keep internal distribution separate from the supply-entry design. The article on bringing mains power into an outdoor enclosure safely covers that upstream connection and its installation requirements.
Which enclosure rating the installation needs
Select the enclosure type from the actual exposure. Type 12 can suit indoor dust and dripping-liquid conditions. Type 4 addresses hose-directed water, while Type 4X adds corrosion-resistance requirements.
Our enclosure ratings are manufacturer ratings for the specified design; the enclosures are not UL listed. Confirm any project requirement for independent evaluation before choosing the enclosure or internal distribution assembly.
An inlet, disconnect operator or cable entry becomes part of the enclosure boundary. Its environmental rating must apply in the installed orientation, with the specified gasket, wall thickness and mounting arrangement.
A sealed operating handle does not establish the rating of its surrounding cutout. Likewise, an internal power strip's approval does not establish the acceptability of the completed control assembly.
If the installation needs only occasional equipment replacement, consider whether retaining an intact molded plug simplifies the design. The article on passing a molded plug through an enclosure opening explains why a larger opening needs an appropriate entry system rather than sealant alone.
Which metal suits the installation
Choose the enclosure material for the site, not for the distribution assembly. The electrical requirements for protective-earth bonding still apply to exposed conductive construction where required.
Powder-coated carbon steel suits indoor and sheltered industrial panels. Its coating protects the surface, but creates an insulating layer at ordinary metal-to-metal joints.
Aluminum can suit weight-sensitive builds. Do not assume that a screw through painted aluminum establishes a dependable protective-earth connection. The bonding hardware must suit the metal, conductor and expected environment.
304 stainless steel is a practical starting point for many indoor washdown and outdoor applications. Consider 316L stainless steel for salt air, brine, chlorides and compatible chemical environments. Neither grade removes the need to check the actual cleaning chemistry.
The custom enclosure material choices allow the body material and dimensions to follow the installation. Specify the material before detailing bonding connections, mounting hardware or cutout finishing.
Set the distribution and disconnect ratings
For an enclosed panel with permanent internal wiring, a terminal-based distribution assembly is often easier to specify than a modified plug-in strip. Use components intended for that wiring method and complete the required assembly assessment.
If serviceable plug connections are necessary, choose an internally mounted receptacle assembly whose instructions permit that use. Preserve its cord and plug unless the manufacturer documents a permitted alternative connection.
A mechanically sound crimp is only one part of the design. It does not establish terminal suitability, insulation spacing, strain relief or continued coverage by the original approval.
Calculate the input load
List each connected device's rated input voltage, frequency, current and starting characteristics. Do not substitute a power supply's DC output current for its AC input current.
For example, three devices rated at 1.2 A each plus one rated at 0.4 A total 4.0 A. That arithmetic applies when those ratings describe the same supply voltage and operating conditions. Starting current, continuous operation and protective-device requirements still need separate checks.
The allowable assembly current cannot exceed the lowest applicable component or conductor rating under its installation conditions. A 15 A strip does not make a 10 A inlet suitable for a 15 A supply path.
Coordinate the upstream protection with conductors, terminals, inlet and distribution components. A strip's internal protective device does not necessarily protect wiring or terminals ahead of that device. Supplementary protection is not automatically a substitute for required branch-circuit protection.
Select an actual supply disconnect
Specify voltage, current, pole arrangement and suitability for the connected load. A resistive-load rating alone may not cover motors, transformers or power supplies with substantial inrush current.
Choose a disconnect intended for external operation through the enclosure wall. Check its mounting method, operating mechanism, terminal covers and environmental conditions.
A rocker switch incorporated into an inlet may provide routine on-off control without meeting the required isolation function. Establish the required disconnection and lockout functions before selecting it.
Never switch or fuse the protective-earth conductor. Select switching of other conductors according to the supply system and applicable equipment requirements.
Mark any terminals that remain energized when the external operator is off. A supply disconnect is not an emergency-stop function or a substitute for machine safety design.
Size around plugs, wiring and heat
Lay out the actual components before choosing width, height and depth. Include the installed dimensions of plugs, terminal covers and the disconnect mechanism, not just their front-panel footprints.
Reserve space for:
- Cable bending without pressure on inlet or receptacle terminals.
- Removal of plugs without disturbing adjacent wiring.
- Disconnect operation throughout the door's travel.
- Terminal access with the specified installation tools.
- Separation or barriers between mains and low-voltage circuits where required.
- Secured excess cord length, away from hot surfaces and sharp edges.
Avoid choosing a shallow enclosure solely because the distribution strip fits on its backplate. A right-angle plug or terminal cover can determine the required depth.
Calculate heat from actual component losses. A power supply delivering 100 W at 90% efficiency dissipates approximately 11 W within the enclosure. Equipment consuming its output inside the same enclosure contributes additional heat.
Do not add the entire nameplate power of externally supplied equipment to the enclosure heat load. Account for losses occurring inside the enclosure boundary.
Internal fans redistribute heat but do not remove it from a sealed box. The explanation of internal fans in a sealed enclosure covers that distinction.
For a compact arrangement combining mains terminals and control components, the article on enclosing a 120 VAC power supply and relay addresses closely related layout constraints.
Mount, guard and bond the assembly
Mount the distribution assembly using its documented brackets or mounting points. Do not drill through its housing or depend on unsupported wiring to hold it in position.
Protect mains terminals against accidental contact using the required barriers, boots or covers. Quick-connect terminals must match the tab dimensions, conductor size, temperature and current requirements. Use the specified crimp tooling and any required insulating enclosure.
Provide strain relief separately from the electrical termination. Neither a crimp terminal nor a solder joint should carry cable pull or twisting loads.
Route the incoming protective-earth conductor to a suitable bonding arrangement. Connect the enclosure and other required exposed conductive parts through a dependable fault-current path. Do not rely on a strip resting against the backplate, incidental mounting contact or door hinges alone.
NEC 250.12 requires removal of insulating coatings at bonding contact surfaces unless the fittings make removal unnecessary. Use a defined connection intended for protective bonding, with hardware suitable for the enclosure material. Do not assume a serrated washer alone makes any painted joint acceptable.
Determine whether doors and removable metal panels need separate bonding connections. Keep the supply neutral isolated from the enclosure except where the applicable system design specifically requires a neutral-to-ground connection.
The enclosure grounding and bonding guide explains the fault-current path and why an earth electrode does not replace the equipment grounding conductor.
Preserve the enclosure boundary
Keep mounting fasteners out of sealing surfaces and gasket compression zones. Where mounting penetrates the outer wall, specify an evaluated sealing arrangement rather than treating an ordinary screw as watertight.
For the inlet and disconnect operator, use the exact component cutout and installation instructions. Check rear clearance, allowable wall thickness, corner geometry and gasket seating before approving fabrication.
The custom stainless enclosure cutout options support drawing-based planning. New openings do not automatically preserve the original enclosure rating.
Complete assembly and verification with the supply isolated and absence of voltage verified under documented electrical safety procedures. Required checks include protective-bond continuity, termination inspection, insulation verification and disconnect operation, using the applicable equipment standard's methods and limits.
What to put on the order
Specify the enclosure and electrical assembly together, even if they are supplied separately. The approval drawing should show component locations, protected terminal zones and the space needed behind every operator.
| Item | What to specify |
|---|---|
| Environment | Indoor or outdoor location, water exposure, contaminants, ambient temperature and condensation risk |
| Enclosure construction | Selected material and required manufacturer-rated enclosure type |
| Acceptance requirements | Required assembly evaluation and any independent listing requirement |
| Supply | Voltage, frequency, supply configuration and upstream protective-device details |
| Distribution | Assembly intended for the installation, mounting method and permitted supply connections |
| Connected loads | Maximum simultaneous input current, starting characteristics and load type |
| External disconnect | Required isolation function, load rating, poles, operating mechanism and lockout provisions |
| Terminals | Conductor compatibility, protective covers, strain relief and access clearances |
| Protective earth | Incoming connection, dedicated bonding locations and required door or panel bonds |
| Dimensions | Width, height and depth in inches, with the complete installed layout and rear clearances |
| Heat | Internal component losses, maximum ambient temperature and proposed thermal management |
| Openings | Manufacturer cutout drawings, wall-thickness limits, seals and installed orientation |
We build custom enclosures from one piece, with the material, dimensions and cutouts defined for the application. Confirm electrical component suitability before approving the enclosure drawing. That avoids designing the enclosure around a modified power strip whose permitted installation remains unresolved.
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 |
|---|---|---|---|
| 6 × 6 × 4 in | 304 stainless | 6 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 8 × 6 × 4 in | 304 stainless | 8 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 10 × 8 × 4 in | 304 stainless | 10 x 8 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can a standard power strip be mounted inside a metal enclosure?
Only when the manufacturer's instructions permit the mounting, enclosed environment and supply arrangement. Check temperature, clearances, plug retention and protection requirements. An enclosure does not extend the strip's approval to an installation outside its documented conditions.
Can the plug be removed and the strip wired to a panel inlet?
Do not assume the original approval covers that change. Use a manufacturer-documented connection option or select a distribution assembly intended for permanent internal wiring. Correct crimping alone does not establish terminal protection, strain relief or acceptance of the completed assembly.
Does a painted metal enclosure need a separate protective-earth connection?
For a mains assembly requiring protective bonding, the enclosure needs a dependable protective-earth connection. Insulating paint must not interrupt that connection. Use bonding hardware intended for the material and follow its instructions, including coating removal unless the fitting makes removal unnecessary.
Is a switched power inlet enough to serve as the enclosure disconnect?
Not necessarily. The switch must provide the required disconnection function and suit the supply voltage, current, pole arrangement and connected load. Some switches provide only routine on-off control. Check isolation, lockout provisions and any terminals that remain energized when switched off.
Does a 15 A power strip make the complete enclosure assembly suitable for 15 A?
No. The allowable current depends on every applicable component and conductor rating under installed conditions. Check the inlet, disconnect, terminals, wiring and distribution assembly. Also verify upstream protection, continuous loading requirements and starting current rather than relying on the strip's marked rating alone.
