What is a critical-component list in a certification report, and why does substituting a part matter?

Main answer · Wecent Editorial Team

Short answer: A critical-component list is the table in a safety report that names the parts that affect safety, with their maker, model, ratings and approvals. Production must use those parts or listed alternates. Swapping a listed part without a lab’s approval means the product no longer matches the tested sample, which can void the approval.

What the list contains

In a safety report, the critical-component list names parts whose failure or change could affect safety. For a charger these usually include the transformer, input fuse, primary capacitors, optocoupler, the output cable and plug, plastic enclosure material and key semiconductors. For each part it lists the manufacturer, model, ratings, the standard it meets and the safety mark or file number.

Why it matters

The test lab tested one design with those parts. The approval says that design is safe. If production uses a different part, it is not the design that was tested, and the lab has not judged whether it is safe in the same way.

What counts as a critical part

Ask the lab or certifier, but typical examples are: – Parts that provide insulation between mains and output. – Parts that carry mains voltage or limit current. – Parts that affect temperature rise. – Materials that must resist heat or flame.

What happens when a part changes

There are usually three routes: 1. Listed alternate. The report already names a second source for the part. Use it, and record the change. 2. Equivalent part. The lab reviews the new part’s data and issues a report update, sometimes without a full retest. 3. New design. If the change is large, a partial or full retest is needed.

How to control it

• Ask the factory for the critical-component list and compare it with the bill of materials every year and on each change.
• Require written notice before any change of critical part, supplier or material.
• Keep photos of the board and parts from approval.
• Check the first lot after any approved change.

A word on cost savings

Replacing a capacitor or optocoupler may save a few cents, but one failed audit or product recall costs far more. Treat any critical part as locked unless the certifier has approved the change.

Where this answer says to confirm with Wecent, the detail is not published on the product page and has to come from the datasheet or the factory. General facts come from the regulators, standards bodies or device makers named in the text.