SELV
Separated Extra-Low Voltage
An extra-low- system supplied from a safety source such as an isolating transformer, kept electrically separate from earth and from every higher-voltage system. Because the voltage is low and there is no path back to earth, touching one conductor cannot drive a dangerous through you — the classic protective measure for shaver sockets and garden lighting.
Where SELV fits in the learning path
The Installation section covers these units:
- Wiring Systems & Enclosures
- Cable Selection & Circuit Design
- Earthing, Bonding & Consumer Units
Curriculum mapping: C&G 2365 Units 203/204/305.
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- C&G 2365 Level 2Sparks Basics
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- Electrical Science — quiz previewFree · Electrical Science
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An extra-low-voltage system fed from a safety source like SELV, but with one point deliberately connected to earth. The earthed reference suits control circuits and electronics that need it, at the cost of losing SELV's complete separation — the difference between the two is a reliable exam question.
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PELV — Protective Extra-Low Voltage
An extra-low-voltage system fed from a safety source like SELV, but with one point deliberately connected to earth. The earthed reference suits control circuits and electronics that need it, at the cost of losing SELV's complete separation — the difference between the two is a reliable exam question.
Read the PELV entryBasic protection
Protection against touching live parts during normal, fault-free service. It is delivered by insulation around conductors, barriers and enclosures around terminals, and placing live parts out of reach. It is the first layer of shock protection; fault protection is the second, and an installation needs both.
Read the Basic protection entryA definition is a start. Using it in a real question is where it sticks.