Clearance & Creepage

It’s obviously gooseberry season, as I receive very little questions for Ask-Away-Friday. So once again, I invite everyone to send in your questions around the development of electronics.

Last week I received the following question: “Electrical safety standards often mention clearance and creepage requirements. If there’s enough space, can you just assume the longest distance (usually the creepage) for the clearance?”

Of course, the short answer is: Yes.

But it does raise the question why you would want to do so. In terms of PCB-development the answer is obvious, since the majority of EDA software is unable to calculate creepage, but they can all handle clearance rules.

Electrical safety standards are also used within components like transformers, common mode chokes, etc., applying the clearance and creepage in there as well. When a component is advertised as “prepared for ”, this usually means that you can achieve a more stringent standard or protection class by increasing the creepage in the PCB lay-out.

So it is possible that you cannot avoid having to maintain separate criteria for clearance and creepage. Let’s look forward to affordable EDA-software that is able to handle creepage rules.

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