Application and arrangements of SELV and PELV circuits

1. SELV - Definition according to BS 7671

SELV - Safety (Separated) Extra-Low-Voltage
Extra-Low-Voltage system (i.e. normally not exceeding 50 V a.c. or 120 V ripple-free d.c.) which is electrically separated from earth and from other systems in such a way that a single fault cannot give rise to an electric shock.

Protection by SELV is used in high-risk situations where the operation of electrical equipment presents a serious hazard to safety. One typical location is Zone 0 in a pool zone which is in the water container itself. The nominal voltage for a pool light connected in zone 0 must not rise above 12V ac or 30V ripple-free dc.

In this system, there is NO return path for current via earth as protective earth conductors are NOT permitted to be installed on the secondary ELV side of the transformer.

Typical applications for SELV systems include:
  • Pool lighting
  • Spa lighting
  • Sauna lighting
  • Bathroom lighting

2. PELV - Definition according to BS 7671

PELV - Protective extra low-voltageAn extra low-voltage system which is not electrically separated from earth but which otherwise satisfies all the requirements for SELV.

Protection by PELV is used where extra-low voltage is required, but the risk of electric shock is much lower than what would be expected for a SELV wiring situation.

A PELV system may include the addition of circuit protection in the secondary conductors of the ELV circuit. Although protective earth is not required on the secondary of a PELV transformer, one can be used should the connected equipment need it.

Typical applications for PELV systems include:
  • Garden lighting
  • General ELV lighting
  • Automation busways
  • ELV machine control circuits 

IEC Requirements for SELV and SELV when tested for insulation resistance

Installation Requirements
Where SELV is used, whatever the nominal voltage, protection against direct contact shall be provided by:
  • barriers or enclosures affording at least the degree of protection according to SASO 980 IP2X or IPXXB, or
  • insulation capable of withstanding a test voltage of 500 V a.c. for 1 min.

  • IEC
  • BS 7671
  • City and Guilds
  • AUS/NZ 3000:2007


  1. IEC/TR 62685 Industrial communication networks - Profiles - Assessment guideline for safety devices using IEC 61784-3 functional safety communication profiles (FSCPs) test electrical appliances

  2. I wanted to thank you for this excellent read!! I definitely loved every little bit of it. I have you bookmarked your site to check out the new stuff you post. Electrician croydon


Select Topics

electric protection Electrical Design power system protection Electrical Safety Fault Analysis Electrical Machines protective relaying circuit breaker electrical protection Electrical Equipment Technical Topics Electrical Installation Power System BS7671 short circuit analysis DC Circuit Earthing System Transformer power system analysis what Direct Current System Energy Efficiency Generator IEC standard Manual Resources Transmission Lines Unbalanced Fault Analysis electrical motor electrical testing grid automation power system automation smart grid tutorial video ebook how motor control substation automation symmetrical components AC Machines Advance Circuit Theory IEC 60364 Renewable Energy Voltage Drop Calculation current transformer electrical grounding schneider electric Circuit Analysis fuse generator protection power system stability quiz switchboard transformer protection ABB Manuals AC Circuit Busbar DC Machines GE Whitepapers General Electric Line to Line Fault National Electrical Code arc flash earth fault loop impedance electric vehicle electrical wiring power plant power system operation selective coordination switchgear video tutorial 3D printing ABB AREVA AUS/NZ 3000 Assignment help Busway Current Nomenclatures Electricity Spot Market G3 technology IEEE C37.2 IEEE/ANSI Device Numbers MiCom NFPA 70E Philippine Electrical Code Terms of use Theoretical UFES VFD ampacity battery building wiring capacitor circuit breaker curve cooling system cooper bussman disruptive technologies electrical earthing electrical harmonics energy industry energy savings engineering education iec 61850 inspection checklist learning process bus protective bonding single line to ground fault transmission line protection variable frequency drive voltage compensation voltage transformer voltage unbalance