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EN50155-Slide6

Although DC voltages below 60V are normally classed as Safe Extra Low Voltage, the railway standard still requires galvanic isolation for additional safety and reliability. For DC/DC converters suitable for 24V, 36V or 48V supplies, 500VAC/750VDC isolation is sufficient. The insulation grade can be functional or basic. High voltage DC is not safe to touch, so DC/DC converters suitable for 96 or 110V supplies which can have inputs that exceed 125V under surge conditions need 1.5kVAC/2.2kVDC isolation. Although not required by EN50155, it is usual for the higher input voltage converters to use supplementary or reinforced grade insulation as this simplifies the risk assessment.

PTM Published on: 2017-04-11