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When designing electronic circuits (PCBs) I often wonder if I should use a polyfuse (aka polyswitch, PPTC, PTC resettable fuse) at the power inputs and outputs or not. So basically what I am asking myself is:

"Is it worth to spend money on a polyfuse in this design?"

Guess the primary reason for using polyfuses is to protect the PCB traces and externally connected wires from melting in case of an error. Further to keep damages caused by any fault low.

Is there a more structured way to decide whether the use of a polyfuse makes sense or not?

SMD polyfuse

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  • \$\begingroup\$ This question is not specifically answerable. Likely your thought path should be "do I need protection" and if so "is a polyfuse suitable". But this depends on details of a specific circuit, it is not generally answerable and so it is not on topic here. You are probably looking for reference materials (for example from a polyfuse manufacturer, in comparison to those from makers of other protection technologies), rather than a strict QA site designed for the efficient handling of specific, narrow questions, not the general introduction to broad topics. \$\endgroup\$
    – Chris Stratton
    Commented Dec 1, 2020 at 15:58
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    \$\begingroup\$ The primary reasons you list apply when faults/errors occur. These are better/cheaper and more reliably served with a regular fuse. \$\endgroup\$
    – Andy aka
    Commented Dec 1, 2020 at 16:27
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    \$\begingroup\$ Wikipedia tells that sometimes polyfuses are used because it is impossible or difficult to replace normal fuses. +1 for the question, because I humbly think that this question could receive an interesting answer telling the standpoint of an experienced professional circuits' designer, who could say something about the reasons that, in real world applications, drive the choice between a normal fuse and a polyfuse. Maybe the probability of a failure is a reason, too. \$\endgroup\$
    – mguima
    Commented Dec 1, 2020 at 16:28
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    \$\begingroup\$ Hoping someone will come along and create a mini-whitepaper on polyfuses in the answer field is the opposite of the purpose of this site. That wouldn't be specific within the rules of the site. The purpose of stack exchange is not to replace wikipedia or manufacturer white papers. Rather the purpose of stack exchange is to efficiently address specific-problem questions which remain after consulting such. \$\endgroup\$
    – Chris Stratton
    Commented Dec 1, 2020 at 17:43

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