SELV
SELV (Safety Extra Low Voltage) describes a voltage that is set so low that there is no danger from excessive body currents when touching it directly, either during normal operation or in the event of a single fault.
If insulation fails, there must still be sufficient protection. In the case of power supply units, this is achieved by galvanic isolation with double or reinforced insulation between the primary and secondary sides. No additional protection against direct contact is required.
The voltage of a SELV voltage source must not exceed the peak value of 42.4 V for AC voltage or superimposed AC voltage and the value of 60 VDC for DC voltage in dry rooms and during intended operation.
In the event of a single fault, the specified voltage limits must not be exceeded for longer than 200 ms. In addition, the peak value of 71 V for AC voltage and the DC voltage value of 120 VDC must not be exceeded. Earthing of the secondary side is not required, but permissible.
See also PELV.
