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Limited Power Source Requirements Help Lower Safety Risks

Many power supplies come with a limited power source (LPS) rating to indicate they pose a reduced likelihood of danger to users. When applicable, manufacturer product pages or data sheets will indicate that the unit is LPS compliant. Because this rating typically appears amid a long list of features and specifications, it’s easy to lose sight of its importance. Here’s a quick overview of what you should know about LPS as you make your selection.


When selecting power supplies, it’s important to remember that power products can potentially present safety risks. LPS is a requirement within the IEC/UL 60950 safety standard for information technology equipment that establishes a maximum output voltage, output current and outdoor power rating for power supplies under normal operating conditions or single-fault conditions. With these limitations, system installers — who may not know all of the various potential fault conditions when choosing wire and cable — can recognize an LPS product as having a reduced risk of electrocution or fire.

Here is a partial summary of the criteria a power supply must meet for LPS compliance. For the complete criteria, be sure to reference the IEC/UL 60950 standard. Note that LPS requires that the unit meet both the current and apparent power limits for output voltages of 30V or less:

  • Output voltage 30V or less
  • Output current 8A or less
  • Output power 100W or less

If the supply has an output voltage greater than 30V up to 60V:

  • Output current cannot exceed 150 ÷ Vout
  • Output power 100W or less

Polytron Devices’ UI72/PA AC-DC power supplies are designed to comply with the LPS standard. These single-output industrial power supplies come in a 4.45 x 1.93 x 1.38 inch (113 x 49 x 35 mm) package and offer outputs from 25 to 72 watts, depending on the model. In addition to compliance with IEC/UL 60950 LPS maximum permitted output ratings, built-in safety features include over current, over voltage and short circuit protection. Over temperature protection is available as an option.

Additional features and specs include:

  • DoE/CoC Tier II compliance
  • LED indication
  • MTBF of 100,000 Khrs.

LPS Compliance Means Less Worry

Your power supply vendor’s datasheet or product page should indicate whether the unit meets LPS specifications. Selecting an LPS-compliant power supply can mean less worry of fire or electrocution, and in some instances, selecting an LPS-compliant power supply may allow you or your system installer to follow relaxed wiring and installation requirements. Our UI72/PA AC-DC power supplies conform to the LPS standard and include built-in protections to give you the reliability industrial systems demand plus enhanced safety characteristics.

For more information about Polytron Devices’ UI72/PA AC-DC power supplies, visit the product page.