This article will help you in identifying and managing critical components. The term critical components is used to identify safety-related components in the test report form as required by clause 4.8 of the standard. Critical components are an important topic –you will either have to demonstrate that each one is safe or provide evidence that it complies with a relevant component standard.

Find out more about critical components in the video below.

While there is no formal definition of critical components, the IEC 60601-1 provides an informal definition. It states ‘all components, including wiring, the failure of which could result in a hazardous situation.’ You should therefore apply your risk management processes to identify which components are critical components.

Hazardous situations due to component failure

The failure of any component can potentially result in a hazardous situation. For example, a fault in the insulation barriers provided by power supplies and power cords could expose the user to an electric shock. A fuse that fails as a short circuit could fail to limit the current to the device, and a fault in a y-capacitor or line filter could present line voltage on the chassis.

Faults in isolating components such as transformers, opto-isolators and solid insulation, could expose users to electric shock and faults in thermal protectors could expose the user to heat. A faulty battery could cause a fire or explode and connectors could fail to provide insulation.

Identifying materials that are inside or part of a fire enclosure is also an important step to take. Examples include the plastic enclosure, printed circuit boards, connectors, insulated cables and components with plastic parts such as insulators, fans, bobbins, relay housings, fuse holders, sleeving and so on. In short, all plastic should be identified as a critical component.

Component compliance

Critical components must be used within their specified ratings. They should be reliable in the conditions of use of the device and they should comply with applicable requirements of either a relevant component standard or the IEC 60601-1.

To check compliance with the requirements, you should assess datasheets and drawings from the manufacturer, test certificates or test reports. You should also check that the component is consistently identified across all documentation.

Below is an example of what should be checked. This is part of a datasheet for a series of fuses with different ratings.

Datasheet for series of fuses

Let us assume, that the ratings of the 1 amp component in the series is suitable for your design. It is indicated in the image below that UL has tested and certified the components in the range 0.25 to 10 Amps.

Always confirm this indication in the datasheet and never trust a datasheet or the website of a component manufacturer.

Check and verify component information

To verify whether the 1 amp fuse in this example has been certified by UL, look it up in the online database. The key information is in the UL file number, typically starting with the letter ‘E’ and then a five-digit numerical code. If a match is found and the information looked up in UL’s database also matches the data for your 1 amp fuse, the check has been successful.

Datasheet for series of fuses

Be sure to check the company information for the component to guarantee that the specific component wanted for use is covered by this online certificate. Also, check that the ratings and limitations from the certificate match the use of the component in your design.

As this documentation is available online, be sure to create your own local copy. This document should be managed in accordance with the requirements of ISO 13485, clause 4.2.4f for documents of external origin.

If you can provide a valid test certificate, it is not necessary to retest the component to ensure that a fault cannot result in a hazardous situation. If a certificate cannot be provided, consider a replacement, or, ask the component manufacturer to perform and certify component testing.

Compiling and maintaining this documentation during development is crucial – by using components that have been tested and certified by UL, VDE or similar certification bodies, time, money and effort is saved.

Data for critical components

The part number, manufacturer, type number and technical data should all be determined in order to uniquely identify each critical component. The standard by which the component complies with and the reference number for the certificate of conformity or test report should also be identified.

Remember to check that the standard is suitable for the component and that a valid edition has been applied. Lastly, check the certificates of conformity for every critical component and any limitations indicated on the certificate.

What to keep in mind when approaching test houses

Documentation should be compiled throughout the design and development stages. The diagram below shows the approach that the test house would probably look like.

Checklist approach test house

Critical components are identified by examining the circuit diagrams, then, their type and manufacturer is identified in the parts list or bill of materials.

Following this, datasheets and drawings are examined to check that each component is used within its specified ratings. Then, there is an assessment of the reliability of the conditions of use for the device.

Lastly, a check of the certificates and any limitations for the specific type of component is carried out. It is a good idea to check these things yourself before design freeze; if done promptly, the process is quite simple.

Critical components list

Would you like to know more about safety for electrical devices?

If you want to know more about the 60601 standard and safety for electrical devices, take a look at our online course Introduction to Safety for Medical Devices and IEC 60601. This comprehensive course has in-depth information and quizzes to test your knowledge and understanding. At the end of the course you will also receive a course certificate, which many auditors will be looking for.

Our online courses are frequently taken by competent authorities, notified bodies and medical device manufacturers and distributors.

Claus Rømer Andersen

Claus Rømer Andersen is an accomplished trainer, consultant and facilitator in the medical device industry. With a background in electrical engineering, he has worked with regulatory navigation, approval management, device testing throughout his whole career.

He is recognized as having a pragmatic and solution oriented approach to helping development teams focus on relevant issues throughout the entire product life-cycle.