Choosing between an open frame and enclosed power supply affects more than your equipment’s physical layout. The PSU format influences thermal management, electrical safety, electromagnetic compatibility (EMC), installation space and the integration effort needed to get the finished product through compliance.

The right choice depends on where the power supply will be installed, what protection the host equipment already provides and the requirements of the complete system.

This guide covers how each format works, where each is used and what engineers, product designers and system integrators should check before deciding.

Key takeaways

• Open frame power supplies are designed for installation inside equipment where the host system provides mechanical protection, airflow and safety barriers.
• Enclosed power supplies have their own protective housing, which adds a physical barrier around the internal components and can simplify integration.
• Neither format is automatically better for thermal performance or EMC. The PSU specification, mounting arrangement, airflow and system design all matter.
• Safety and EMC requirements should be considered alongside output power, output voltage, space constraints and environmental exposure from the start of the design.
• The lowest unit cost is not always the lowest project cost. Mechanical design, thermal management, compliance and service cost all contribute to the total.

Open frame vs enclosed power supply: the quick answer

The key question is whether your equipment already provides the protection and environmental control the PSU needs.

An open frame power supply suits applications where the PSU is installed inside a controlled enclosure. The host equipment provides the protective enclosure, user-access barriers, mounting points and airflow needed for safe, reliable operation.

An enclosed power supply has a protective chassis around its circuitry. It adds mechanical protection and can make installation easier where a more self-contained solution fits the equipment design.

The choice isn’t as simple as “open frame for compact equipment, enclosed for harsh environments”. Both formats are available across a wide range of power ratings and applications, so the decision depends on the product specification and the finished equipment.

What is an open frame power supply?

An open frame power supply is an internal AC/DC power supply with no complete protective housing around its electronic components. The circuit board and components are exposed, and the PSU is designed to be installed inside host equipment that provides the necessary protection.

Without a full enclosure, the open frame format gives designers more freedom over where the PSU sits and how air flows around it. This makes it useful in compact designs and tight spaces where every millimetre of installation space counts.

Some open frame units are supplied on a metal frame or bracket, often called a U-frame or U-channel. This adds a mounting structure without fully enclosing the electronics.

Where the host equipment takes over

“Open frame” doesn’t mean a PSU is unsuitable for safety-critical applications. It means the finished equipment must provide appropriate protection and meet the relevant safety requirements.

Many open frame units carry recognised safety approvals as components. Those approvals assume correct installation. They don’t remove the need to assess the complete system, including protection against accidental contact, insulation distances and earthing.

Ideal Power’s open frame range includes compact AC/DC units designed for direct integration into electronic equipment.

What is an enclosed power supply?

An enclosed power supply houses its electronic components within a protective chassis, usually a ventilated metal case. Connections are typically made through a terminal block on the outside of the unit.

The protective housing guards the internal circuitry and helps prevent accidental contact with live parts. Combined with defined mounting points and accessible connections, this can make installation more straightforward.

Ideal Power’s enclosed range includes AC/DC power supplies for industrial automation, telecommunications and specialist electronic systems. Models are available with different output voltages, power ratings, cooling arrangements and safety approvals.

An enclosure provides physical protection, but don’t assume an enclosed PSU is automatically suitable for outdoor use or harsh environments. Environmental protection depends on the specific design, the operating conditions and the equipment enclosure around it.

Key differences between open frame and enclosed power supplies

The main difference is physical format, but that affects several parts of the system design.

Physical protection

An open frame unit relies on the host equipment to provide mechanical protection and prevent access to exposed components.

An enclosed power supply has its own protective housing, adding a physical barrier between the electronics and the surrounding equipment.

Space and form factor

Open frame power supplies suit compact designs where installation space is limited, or where the PSU must fit a bespoke internal layout.

Enclosed units have a fixed form factor, which can be harder to fit into tight spaces but makes mounting and wiring more predictable.

Thermal management

Open frame units work well where the host system provides controlled airflow across the components.

Enclosed units may use convection cooling or forced air cooling from an internal fan, depending on the design. With either format, check the manufacturer’s operating temperature range, cooling requirements and derating curves.

Electrical safety

With an open frame PSU, the host equipment must protect against accidental contact and meet the relevant insulation, creepage and clearance requirements.

An enclosed PSU provides additional physical protection, but the complete system must still meet the applicable safety standards.

EMC performance

Both formats need careful attention to electromagnetic compatibility. An enclosed metal chassis can help with shielding. Open frame designs leave more of the EMC behaviour to the host equipment’s layout, grounding and enclosure.

Cost

Open frame units can have a lower unit cost but may need more mechanical, thermal and safety integration work. An enclosed unit can cost more as a component but may reduce that additional design effort.

Where are open frame power supplies used?

Open frame supplies suit equipment that already has a controlled enclosure around the PSU. Common applications include:

• Embedded systems and embedded electronic equipment
• Industrial control systems
• Communication and networking equipment
• Instrumentation and test equipment
• AV and IT equipment
• LED lighting systems
• Certain medical devices and laboratory systems
• Compact electronic products where installation space is limited

The format also suits designs where the engineer wants to control the PSU’s mounting orientation and airflow, rather than work around a fixed housing.

With an open frame PSU, the host equipment becomes part of the power supply’s protection. Mechanical protection, electrical safety, thermal performance and EMC all need assessing at system level.

Where are enclosed power supplies used?

Enclosed power supplies suit applications where extra physical protection around the PSU is useful, or where their mechanical format makes installation easier. Typical applications include:

• Industrial automation and control equipment
• Control panels and cabinets
• Communication equipment
• Commercial AV and broadcasting equipment
• Embedded systems
• Instrumentation
• Security and monitoring equipment
• Other installed industrial equipment and commercial systems

Ideal Power’s enclosed range includes models designed for industrial control and automation, network equipment, signal distribution, commercial AV, broadcasting and control panels.

Enclosed units are often a practical choice for less controlled environments, such as a control cabinet that service personnel open regularly. The protective housing reduces the extra mechanical protection needed around the PSU, but the finished equipment still needs to suit its operating environment.

Thermal management: which format performs better?

Thermal management is one of the most important factors in power supply selection. There’s no fixed rule that open frame supplies always run cooler or that enclosed units always run hotter.

An open frame design can let air circulate more freely around components, particularly where the host equipment has a well-designed airflow path. This can help heat dissipation in compact systems.

Enclosed power supplies can also achieve good thermal performance through convection or forced air cooling. The enclosure is designed around the unit’s own cooling method, which gives the manufacturer more control over internal airflow.

Convection and forced-air ratings

Many open frame datasheets quote two power ratings: a lower rating with convection cooling and a higher rating with a specified forced airflow.

If your design relies on the higher figure, the host equipment must deliver that airflow reliably for the life of the product. If it can’t, design around the convection rating instead.

Temperature and long-term reliability

Operating temperature has a direct effect on long-term reliability. Electrolytic capacitor life is a common limiting factor, and a widely used rule of thumb is that it roughly halves for every 10°C rise in temperature.

Running a PSU cooler, through better airflow, lower load or a higher-rated unit, can extend its service life and reduce maintenance and replacement costs.

What to check on the datasheet

When comparing products, look beyond the headline power rating and check:

• Operating temperature range
• Derating curves for temperature and, where given, altitude
• Cooling method and required airflow
• Mounting orientation
• Clearance around the PSU
• Efficiency at the expected load
• Maximum continuous load at the actual ambient temperature

A 500W or 600W PSU won’t necessarily deliver its full rated output under every operating condition. Assess thermal performance against the real environment the power supply will operate in.

Safety considerations

Address electrical safety early in the design, rather than treating it as a final compliance check.

Protection against accidental contact

An open frame PSU exposes its live parts to the surrounding equipment. The host system must prevent user access to hazardous voltages and protect against electric shock.

It must also maintain the required insulation, creepage and clearance distances. Mounting screws, standoffs and nearby metalwork can create an unintended conductive path to live parts if the manufacturer’s keep-out areas and spacing requirements aren’t followed.

An enclosed PSU provides a protective housing around its circuitry. This can simplify compliance for the accidental-contact requirements, but it doesn’t make the finished product compliant on its own.

Class I and Class II power supplies

Class I power supplies rely on a protective earth connection for protection against electric shock. On many open frame units, this connection is made through a designated mounting hole or earth terminal, which must be bonded to the host equipment’s protective earth.

Class II power supplies use double or reinforced insulation instead of a protective earth. Protection classes are defined in IEC 61140.

Class II isn’t another name for an enclosed power supply. Both open frame and enclosed units can be Class I or Class II, so check the classification on the individual PSU’s datasheet against the requirements of the finished product.

Which safety standards apply?

The applicable safety standard depends on the finished equipment.

IEC 62368-1 is the product safety standard for audio/video, information and communication technology equipment. It takes a hazard-based approach, with safeguards against electrical and other energy sources, and can also apply to components and subassemblies intended for that equipment.

IEC 61010-1 covers safety requirements for electrical equipment for measurement, control and laboratory use. It’s relevant to many instrumentation and test applications.

IEC 60601-1 covers basic safety and essential performance for medical electrical equipment.

Medical equipment

Medical applications add specific requirements. IEC 60601-1 defines means of protection for operators (MOOP) and patients (MOPP).

Equipment with patient contact typically needs 2 × MOPP between the mains input and the output, which is associated with 4,000VAC isolation and 8 mm creepage. Leakage current limits also apply and depend on the type of applied part.

Check that the PSU’s medical approval, isolation rating and leakage current match your application. A medical approval on one model doesn’t extend to a different series.

EMC considerations

The PSU is only one part of the finished system’s EMC performance. Cable routing, grounding, filtering, enclosure design and the interaction between components all affect emissions and immunity.

With an enclosed unit, the metal case can help contain electromagnetic interference generated by the switching circuitry.

With an open frame unit, the host equipment’s layout and enclosure play a bigger role. Open frame PSUs are often EMC-tested mounted on a metal ground plane, and achieving similar results in your product may depend on reproducing that mounting and earthing arrangement.

Check the test conditions on the datasheet, and follow any recommended EMC circuit where higher requirements apply.

Environmental conditions

Environmental conditions affect format choice as much as the electrical specification.

Dust, humidity, condensation, vibration and temperature extremes all affect long-term reliability. Neither format is protected against all of them by default.

IP ratings

Many enclosed industrial power supplies are rated IP20. This protects against finger contact but not against dust or water ingress.

For wet, dusty or outdoor installations, check the product’s stated IP rating. You may need a sealed PSU or an additional equipment enclosure.

Conformal coating

Some open frame power supplies are available with conformal coating, which adds protection against moisture and contamination on the circuit board. Check availability and the coating specification with the supplier before relying on it.

Open frame vs enclosed: what about cost?

Unit cost is only one part of the decision.

An open frame PSU may cost less because it doesn’t need a full protective housing. The finished product may then need extra mechanical protection, mounting hardware, shielding or thermal management.

An enclosed PSU may cost more as a component but can reduce integration effort where its housing and defined connections fit the equipment design.

The better question isn’t “Which PSU costs less?” but “Which PSU gives the lowest overall cost structure while meeting the technical requirements?” For larger projects, this can include:

• PSU purchase price
• Mechanical design
• Additional protective components
• Thermal management
• EMC development and testing
• Safety assessment
• Assembly and installation
• Future replacement and service cost

The answer varies from one application to another.

Other internal power supply formats

Open frame and enclosed units aren’t the only options. If neither fits, consider:

• U-frame power supplies: an open frame board on a metal bracket, adding mounting strength without a full enclosure
• DIN rail power supplies: designed for control panels and cabinets, with standard rail mounting
• PCB mount power supplies: compact modules soldered directly onto the host circuit board

How to choose the right power supply

Start with the equipment, not the PSU. Consider where the unit will be installed, how much space is available and whether the host equipment already provides a suitable protective enclosure.

Check thermal performance next. Compare the PSU’s operating temperature, cooling method, required airflow and derating curve against the actual operating conditions. A compact open frame unit may suit one application and not another if airflow or clearance is insufficient.

Establish the safety and EMC requirements early. Identify the applicable standards, protection class and earthing arrangement, accidental-contact protection, creepage and clearance, grounding, filtering and cable routing.

Confirm the electrical specification: input voltage, output voltage, current, power rating, efficiency and protection features.

Considering all these factors together makes it easier to select the right power supply format without unnecessary integration or redesign work later.

Why choose Ideal Power?

At Ideal Power, we supply a wide range of internal power supplies, including open frame chassis power supplies and enclosed power supplies for different equipment and integration requirements.

Our range covers multiple power ratings, output voltages, form factors and recognised safety standards, giving engineers options for different applications.

We help you look beyond voltage and wattage by considering installation space, thermal management, cooling, EMC, safety requirements, mounting and operating environment.

Whether you’re developing new equipment or replacing an existing PSU, choosing the right format early reduces integration problems and redesign work.

If you’re not sure whether an open frame or enclosed power supply is right for your application, speak to Ideal Power about your requirements, and we’ll help you identify suitable options.