Explanation Of Terms - Siemens sirius System Manual

3.1.4 Explanation of terms

Safety extra-low volt-
age
Functional
extra-low voltage
PELV
SIRIUS System Manual
GWA 4NEB 430 0999-02b
Safety extra-low voltage (SELV) allows circuits with a rated voltage of up to
50 VAC or 120 VDC to be operated ungrounded. The higher voltage is safely
isolated from the SELV circuits.
Safety extra-low voltage helps protect people.
Functional extra-low voltage (FELV) allows circuits with a rated voltage of up
to 50 VAC or 120 VDC can be operated. It does not, however, meet the
requirements of safety extra-low voltage and is therefore subject to additio-
nal conditions. FELV is implemented using a ground terminal.
Functional extra-low voltage helps protect devices (e.g. programmable con-
trollers).
PELV (protective extra-low voltage) has the same requirements as safety
extra-low voltage, except for the fact that the circuit and/or exposed conduc-
tive part is/are grounded (so it is basically grounded SELV).
3RT1/3RH1 contactors
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