Put the control transformer inside the enclosure only when its losses, clearances, weight and wiring fit the completed panel. Use a separate enclosure when the transformer consumes too much thermal capacity or crowds protection and service access. Mounting it outside without suitable protection is not a complete solution.
For a 380 VAC to 220 VAC application, voltage conversion alone does not determine the enclosure arrangement. You also need the transformer rating, frequency, load profile, installation instructions and available fault current. Make the enclosure decision from that information before releasing the backplate and cutout drawings.
Define the environment before choosing the location
Record the highest surrounding air temperature while the equipment operates, including seasonal and process-related peaks. A nearby oven, hot pipe or sunlit wall can make room temperature an unreliable design basis.
Next, identify water, dust, oil, cleaning chemicals and airborne salts. These conditions determine whether outside-air ventilation is practical. A fan that pulls cool air into a dry electrical room may pull moisture into a washdown panel.
Compare three arrangements:
- Inside the main enclosure: fewer interconnecting entries, but transformer losses heat the controls and consume backplate space.
- Inside a separate enclosure: heat and weight move away from sensitive controls, but protection, isolation and interconnecting wiring need coordination.
- A transformer designed for exposed installation: acceptable only where its own construction and installation instructions suit the environment.
Do not treat a bare transformer attached to an enclosure wall as equivalent to a protected external installation. Accessible terminals, hot surfaces, mechanical damage and environmental exposure still need attention.
Use the transformer enclosure cooling assessment for the detailed thermal evaluation. The decision here is whether the transformer should share the control enclosure at all.
Choose the rating for the completed arrangement
Select the enclosure rating from the actual exposure, not from the transformer voltage or its apparent power rating. An indoor dust application and an outdoor washdown installation can need different enclosure designs around identical electrical equipment.
Our stainless wall-mount enclosures are rated NEMA 4X / IP66 by the manufacturer; not UL listed. Check whether your project requires a third-party listing before selecting an enclosure.
NEMA 250 and IEC 60529 address enclosure protection, but neither rating alone establishes thermal capacity. A sealed enclosure can exclude water while allowing its internal air to become too hot.
If water protection requires a sealed arrangement, evaluate passive heat rejection or suitable closed-loop cooling first. Adding ordinary ventilation openings changes the protection provided by the enclosure. Any cooling assembly and its installation must support the required final rating.
A separate transformer enclosure also needs a rating appropriate to its own location. Moving it beside the main cabinet does not remove washdown, dust or rain exposure.
For rating fundamentals, use the NEMA enclosure types guide. State the required protection for both enclosures whenever the transformer is housed separately.
Match the material to exposure and mounting load
Material selection follows the environment, while mechanical design follows the installed transformer weight. Neither decision should be made from voltage alone.
304 stainless steel is a practical starting point for many indoor washdown and outdoor installations. Consider 316L where salt air, brine or chloride exposure makes additional corrosion resistance appropriate. Confirm compatibility with the actual cleaning chemicals, concentrations and temperatures.
For dry indoor installations, a custom powder-coated carbon steel enclosure may suit the application. We build custom enclosures with the material, dimensions and cutouts defined for the specified design.
Do not select stainless steel as a substitute for a heat calculation. Surface finish, exposed area, mounting arrangement and airflow all affect passive heat rejection. Changing metal grade does not establish an acceptable operating temperature.
Also obtain the transformer's mass and mounting-hole pattern. The backplate, fasteners, mounting feet and supporting structure must carry the complete installed load. Include handling and vibration loads where applicable. Do not assume that sufficient empty space means sufficient mechanical capacity.
Reserve thermal capacity before backplate space
Use transformer losses in watts for the enclosure heat budget. The VA rating describes electrical capacity, not the heat released inside the box.
Request no-load loss and operating-load loss information from the transformer manufacturer. Confirm whether a published loaded-loss figure includes no-load loss before adding the figures together. Include the actual duty cycle and any condition where the transformer remains energized while the machine is idle.
The transformer partial-load heat-loss assessment covers that calculation in more detail. Do not assume that lightly loaded operation eliminates transformer heating.
For a hypothetical selection check, suppose the transformer releases 30 W at the intended operating load. The remaining controls release another 45 W. The enclosure must then reject approximately 75 W, excluding solar gain and any other uncounted sources.
At 104°F [40°C] ambient, a 122°F [50°C] internal-air limit permits only an 18°F [10°C] rise. At 75 W, that requires an effective enclosure-to-ambient thermal resistance no greater than approximately 0.13 K/W. This is a mathematical ceiling before design margin, not a prediction for a particular enclosure.
Use the lowest applicable component ambient limit, including required derating. A transformer winding temperature limit is not the allowable surrounding-air temperature for nearby electronics. Check local hot spots as well as average enclosure air temperature.
A larger enclosure can provide more heat-transfer area and better separation. However, a wall, adjacent cabinet or blocked side can reduce its effective exposed area. Obtain a thermal assessment for the actual mounting configuration.
Choose a separate transformer enclosure when the shared arrangement cannot meet temperature limits with reasonable margin. Separation is especially useful when sensitive controls have a lower ambient limit than the transformer.
Check depth, protection and wiring together
Lay out the transformer, its protective devices and the actual conductor routes before choosing outside dimensions. Allow the installation clearances specified by each device manufacturer; there is no universal transformer clearance suitable for every design.
Keep temperature-sensitive controls out of the transformer's rising warm-air path where practical. Provide access to terminals without removing unrelated equipment. The component layout guidance for sealed enclosures explains how placement affects local temperatures.
Depth needs a separate check. Transformer projection, terminal covers, cable bends and door-mounted equipment can overlap even when the backplate drawing looks spacious. Nominal inside depth is not the same as usable clearance above an installed mounting panel.
For example, the 24 x 20 x 10 in 304 stainless wall-mount enclosure has outside dimensions of 24 x 20 x 10 in. The 30 x 24 x 12 in 316L stainless wall-mount enclosure has outside dimensions of 30 x 24 x 12 in. Both dimensions are height x width x depth; neither establishes transformer fit or thermal suitability without a layout.
For a conventional arrangement, supply the transformer branch downstream of the main disconnect through appropriately selected protection. Do not move the primary connection ahead of the disconnect merely to simplify wiring or keep controls energized.
Coordinate primary and any required secondary protection with conductor ratings, transformer instructions, inrush and applicable electrical rules. Also verify interrupting ratings and the completed panel's short-circuit current rating. Transformer VA alone is insufficient to select protective devices.
A 380 VAC to 220 VAC nameplate does not identify every required connection detail. Verify phase configuration, frequency, taps and grounding arrangement against the manufacturer's diagram. Do not assume that every terminal marked 220 VAC is referenced to neutral or earth.
If any circuit intentionally remains energized with the main disconnect open, resolve its isolation, segregation and identification during design. The incoming line compartment design article addresses the enclosure implications of incoming supply equipment.
Mount and seal without creating another problem
Use the transformer's approved mounting orientation and attachment points. Support its weight through the mounting panel and enclosure structure, not through an unsupported cutout or thin cover.
Keep mounting hardware, cable entries and wiring clear of the door gasket and latch sweep. Provide room to reach branch protection and transformer terminals after wiring ducts are filled. Maintain the required working space outside the enclosure as well.
When using a separate enclosure, define the interconnecting cable or raceway route before placing either box. Each penetration needs a suitable fitting, sealing surface and installation method. A large connection opening can undermine both environmental protection and the intended thermal separation.
Bond exposed conductive parts and the transformer frame as required by the equipment instructions and applicable electrical rules. Protective earth is not a normal load-current path, and it must not be interrupted by the main disconnect. Use the enclosure grounding and bonding guide for the enclosure connection details.
Perform installation work under appropriate isolation and lockout procedures, with absence of voltage verified by qualified personnel. Plan temperature verification using suitably installed sensors so routine checks do not require opening energized equipment.
During commissioning, evaluate the closed enclosure at the expected operating load and representative ambient conditions. Record temperatures near the transformer and the most temperature-sensitive components. A short unloaded run does not validate a fully loaded panel.
Put the inside-or-separate decision on the order
Specify the arrangement explicitly rather than leaving transformer placement to assembly. Include the thermal assumptions and mechanical drawing with the enclosure requirements.
| Order item | Information to specify | Acceptance check |
|---|---|---|
| Transformer arrangement | Shared control enclosure or separate transformer enclosure | Both locations shown on the installation drawing |
| Environment | Maximum ambient, water, dust, chemicals and solar exposure | Conditions match the thermal and material assessments |
| Enclosure protection | Required manufacturer-rated enclosure type and any project listing requirement | Completed entries and cooling arrangement support the requirement |
| Material | 304, 316L or another custom material appropriate to exposure | Chemical compatibility and structural needs reviewed |
| Outside dimensions | Height x width x depth in inches, with drawing references | Component envelopes and service access fit |
| Transformer data | VA, voltage, phase, frequency, losses, weight and mounting pattern | Manufacturer documentation attached |
| Thermal budget | Transformer losses, other component losses and allowable internal temperature | Assessment includes margin and actual mounting conditions |
| Electrical layout | Disconnect, branch protection, terminals, bonding points and wiring routes | Protection and isolation coordinated with the electrical design |
| Mounting and cutouts | Backplate details, support requirements and every penetration | Approved drawing includes sealing and access clearances |
| Verification | Closed-panel temperature checks at defined operating conditions | Component limits and derating requirements satisfied |
Select from stainless wall-mount enclosures only after the fit and thermal checks are complete. If neither catalog depth nor backplate area supports the design, specify custom dimensions instead of compressing clearances.
Custom work starts from the approved drawing. Custom enclosures are delivered in 10 business days, anywhere in the world, counted from your approval of the drawing.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 24 × 20 × 10 in | 304 stainless | 24 x 20 x 10 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 30 × 24 × 12 in | 316L stainless | 30 x 24 x 12 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can a control transformer go inside the main control enclosure?
Yes, when the completed enclosure can reject its losses without exceeding component temperature limits. Confirm mounting strength, manufacturer clearances, terminal access, conductor space and coordinated protection. Use the transformer’s operating losses in watts, not its VA rating, to assess its thermal contribution.
Is mounting the transformer outside always better for cooling?
Not automatically. A separate enclosure can keep transformer losses away from sensitive controls, but it still needs an appropriate environmental rating, heat assessment, mounting support and coordinated isolation. A bare transformer mounted externally is suitable only when its own construction and installation instructions permit that application.
Can transformer VA be used as enclosure heat in watts?
No. VA describes electrical capacity, while enclosure heating depends on transformer losses. Obtain manufacturer loss data for the expected load and confirm whether the published figure includes no-load losses. Include other internal equipment losses when assessing the shared enclosure.
Does selecting a larger enclosure guarantee the transformer will fit and stay cool?
No. Enclosure dimensions establish only part of the decision. You must check actual usable mounting space, installed depth, terminal access, manufacturer clearances, support strength and heat rejection. A larger box may help, but its mounting location and exposed surface area affect the result.
Does a separately enclosed transformer still need coordinated branch protection?
Moving the transformer does not remove its protection or isolation requirements. Coordinate the primary and any required secondary protection, conductor sizing, bonding and interconnecting wiring with the electrical design. Confirm that the disconnecting arrangement clearly identifies which circuits are isolated and whether any remain energized.
