As electrification advances, ensuring the reliability of thermoplastic components under high voltage becomes critical. In this session we discuss that dielectric material failures can be triggered by both intrinsic material properties as well as in the external environment. Specifically focusing on the case of extrinsic -environment controlled- breakdown, zooming in on why thin parts have higher dielectric strength [in kV/mm] and why parts are stronger in DC than in AC. Finally, we briefly touch upon our current work on the topic of electro-ageing and safe operating voltage thresholds, aiming to create knowledge to design safer, longer-lasting components.