If you’re bringing ac power directly into your new product, then the implementation methods to get a safe device need to be carefully considered as part of the design. If you don’t, getting things wrong with ac power can lead to deadly devices, and smoke-filled outcomes.

The multitude of devices now using low-voltage dc power provided from an external ac-dc converter allows many EEs to remain blissfully unaware of high-power safety considerations. Using external ac adapters allows designers to largely ignore many high-voltage product-safety requirements. Designing with power inlets under 25 V, where the “Extra Low Voltage” (ELV) concept is applicable, simplifies things a lot, putting safety issues largely in the hands of the designer of that ac adapter.

Many older (especially prior to 1960) electrical products were inherently unsafe or could become deadly with a single fault failure. Metal enclosures (prior to the widespread use of plastics) and a lack of a ground safety made for a deadly combination. Thankfully, consumer electronic products have a fairly short life, so many of those devices are now obsolete.

Most EEs deal with ELV devices that are subdivided into “Separated ELV” (no ground return path used) and “Protected ELV” (a ground earth safety is present). Recently, IEC 62368-1 (Safety Requirements for Audio/Video, Information & Communication Technology Equipment) has become the standard for ELV safety, and has more carefully defined ELV devices as the “ES-1 region” that limits both current and voltage. For ELV devices, safety requirements are very minimal, with some form of overcurrent protection and a non-conductive enclosure generally being sufficient.