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Does IEC 62368-1 2nd Ed or 3rd Ed require an additional external fuse to be added to an already certified Annex CC current limiter in PoE Circuits?

More specifically you asked:  We are using a POE IC manager for POE Circuit indoor. This IC has an embedded current limiter and the IC is certified as a 60950- annex CC current limiter. Hence no need to put any external fuse for limited power source protection. Now if we migrate to 62368-1, I was informed that we need to put external fuses. Is this true ? Which edition asks for this fuse - second or third edition?


In response, such an external fuse requirement for PoE circuits is not written in either IEC 62368-1 2nd Ed nor 3rd Ed.


However, we have no detailed information about the PoE circuit.


Two possible scenarios are:

- the additional fuse is located in front of the IC Current Limiter (1), or

- the fuse is located after the IC Current Limiter (2)


If (1) is applicable, consider that using a certified current limiter component is the first step to ensure safe product design.  However, in addition, it must be checked, how the component is used in the end-product application. The final acceptance must be done in combination with the circuit analysis and checking any “Conditions of Acceptability” of the component, which are normally defined during the component certification.


Each Condition of Acceptability (CoA) for example of UL recognized component must be considered when used in an end-application. Because such IC’s may need to be supplied by circuits that are itself limited in voltage, current and power. (Please check also Product IQ on www.ul.com.) That could be the reason for the additional fuse requirement.


If (2) applies and the product will be evaluated according to IEC 62368-1 3ed., IEC 62368-3 also may apply. Sub clause 5.3.2, DC power transfer interconnection to other equipment, requires that Power Sourcing Equipment (PSE), under abnormal operating and single fault conditions, not have available output power that exceeds the specified fault current rating of the specific industry specification, like USB.  This also could impact the design.


The complete answer to this topic is complex, and there appears to be a specific, detailed construction that needs review / analysis. Therefore, you are encouraged to contact UL for an in-depth consultation, either via your local account executive or via https://62368-ul-solutions.com/contact-ul.html.

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