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Safety Alert - Uninterruptible Power Supplies


Health and Safety Executive issue safety alert following two fires caused by the same faulty capacitor.



In 2018 a fire occurred in an industrial UPS system manufactured by Vertiv Infrastructure, previously known as - Emerson / Chloride.  The fire was caused by the dangerous failure of ICAR branded polypropylene capacitors located in the UPS unit which carry out AC voltage waveform correction.


Enquiries by the Health and Safety Executive have found that another ICAR branded polypropylene capacitor was responsible for a similar UPS system fire in 2011.


Both models of affected capacitors were made by ICAR of Monza, Italy.


The model numbers are:

ICAR LNF-P3B-200-27 (2018 incident)

ICAR LNF-P3X-200-38 (2011 incident)


Both capacitors are of polypropylene film construction and are intended to be ‘self-healing’ as, when a fault occurs within a discreet area of the capacitor, there is localised heating which results in internal isolation of the faulty area allowing the capacitor to continue in service.  However in the above incidents excessive heating resulted in a dangerous failure and subsequent fire within the UPS cabinets.


Self-healing polypropylene capacitors have a limited life span which can be affected by factors including service duty and ambient temperature.  Methods to identify the need to replace the capacitors may include techniques such as;

  • capacitance testing
  • observation of bulging and of discolouration


However these methods may not be reliable indicators of the remaining life span of these particular capacitors.


UPS system manufacturer Vertiv Infrastructure Ltd has taken steps to alert known users of its UPS systems which may have contained the affected capacitors about this safety issue.


The importer of the capacitors (PSL Assemblies Limited) has taken steps to alert one customer known to have purchased the affected capacitors.


Actions Required


Dutyholders are advised to take a precautionary approach and consider prompt replacement of both capacitor models where these have been identified in UPS systems or other industrial equipment.


Dutyholders are also advised to review ventilation and cooling requirements for UPS systems to ensure that acceptable operating temperatures are not exceeded

For more information please visit the HSE Website

Posted on: August 9th, 2019 by


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