In general, we recommend using a test level equivalent to that for control and signal lines (e.g., Level 1: 0.5 kV) as the basis for consideration.

Most DC power inputs are on the secondary side of an AC/DC converter. Because external noise is attenuated as it passes through the filter circuit and isolation transformer in the AC power supply unit, the same high level of immunity as on the primary-side AC power line is not required.

Rather than classifying by the voltage value itself, it is reasonable to treat the input as having characteristics similar to a “signal/control port” under the standard. However, if the DC wiring is exposed outdoors or the cable length exceeds 3 m, Level 2 (1 kV) or higher may need to be considered.