Requirement on bridging between primary circuit and protective earth by SPD in equipment is described in clause 5.5.7 of [IEC 62368-1]. However the standard does not take into consideration the lightning voltage which is larger than that appears in the conditions considered in overvoltage category II, and it does not provide the requirements necessary for lightning protection of class II equipment without earthing in which bridging by SPD/SPCs is usually applied. It is necessary to clarify the electrical requirements for SPDs/SPCs in order to realize both resistibility and safety of telecommunication systems. This Recommendation analyses the influence on human safety of lightning measures bridging across insulation by SPDs. This Recommendation provides guidance for design of lightning protection and requirements of SPDs from the human safety standpoint. The requirements on SPDs/SPCs in MSPD (multi-service SPD) external to the equipment and SPDs installed on lines in a building are not within the scope of this Recommendation.