Distributed Energy Resources (DER) operating in radial parts of the distribution network, at low and medium voltage levels, are often considered as a cause of fail-to-trip as well as incorrect trip of over-current protection. The EU-DEEP project has developed the "hosting capacity" concept, a general methodology that determines the amount of DER which can be operated in a sub-network with an acceptable level of inconvenience. Initially introduced for quantifying the impact on voltage quality, this concept has been extended to the protection scheme performances. Qualitative and quantitative studies have been performed. Simple closed form approaches have been completed using detailed dynamic simulations to assess more precisely the risks of degraded performances of classic protection systems in presence of significant penetration of DER in distribution.