以下引自EN 60950-1-2006 clause 2.10.2 Determination of working voltage
g) The WORKING VOLTAGE between any point in the PRIMARY CIRCUIT and earth, and between any point in the PRIMARY CIRCUIT and a SECONDARY CIRCUIT, shall be assumed to be the greater of the following:
– the RATED VOLTAGE or the upper voltage of the RATED VOLTAGE RANGE; and
– the measured voltage.