Extra-low Voltage Electrical Practice and Wiring

1. Extra-low Voltage Electrical Practice and Wiring Accessories & wiring examples Written by Ray Miller © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

2. Introduction This slide show provides an overview of some accessories used in ELV wiring as well as the application of these accessories. © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

3. Content • Overview • Warnings • Wiring protection fuses and circuit breakers • Current measurement • Circuit control and voltage regulation • Examples of wiring practices © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

4. Overview • Components and ELV accessories should be: • SAFE • Used correctly as per Aust. Standards and manufacturers’ recommendations • Rated to suit the application under worst case conditions • Be reliable for the life of the energy system • Be designed to work in with other components © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

5. Vocabulary • ELV = Extra-low voltage as defined in Australian Standards © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

6. Accessories • ELV surface mounted power socket • Rating 15 A but only used to a maximum of 10 A continuous • Labelling System voltage and rated current eg 48 V 10 A © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

7. Warning:not to be used for ELV! • Three pin 240 V a.c. (LV) accessories (eg plugs and sockets etc) are not to be used for wiring ELV © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

8. Wiring Protection (fuse switch) • Wiring protected by fuses combined with switch function • Example of a combined set of 3 fuses formed into a switch assembly • Used for battery isolation Open Closed © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

9. HRC fuse for fuse switch • Typical fuse fitted to a fuse switch • Type HRC fuses • Rating 160 A continuous © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

10. Wiring Protection (fuse switch) • 25 A fuse switch • Holds 3 fuses or separate circuits • Suitable for SELV circuits • Clear labelling © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

11. Wiring protection: Circuit breaker d.c.operation • Similar characteristics to HRC fuse • Short circuit and over current protection • Din rail mounting • Can be Reset • Dual use as a switch and wiring protection • Thermal (long-term) and magnetic (short term) operation © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

12. Wiring protection:Circuit breaker d.c. thermal • Thermal circuit breaker • Wiring is only partly protected, for long- term over-current • Very slow to respond to large high current overloads © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

13. Wiring protection:Circuit breaker d.c. • Auxiliary set of low current contacts fitted • The change-over contacts can be used as a remote indication of the circuit breaker state Auxiliary contacts Main connections © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

14. Switch used for lighting • LV switch used for ELV d.c. • Rated 10 A 240 V a.c. • Presses into switch plate • Has loop terminal • Change-over option • X terminal connected to supply is centre of change-over • Terminal 1 normally connected to load/light © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

15. Measurement, amp meter • Analogue amp meter • Integrated 50 A current shunt • Powered by current through shunt • Simple and long-life solution for current monitoring © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

16. Current Shunt • A very low value but known resistor • Used for measuring circuit current • Calibrated in mV per per amperes eg 50mV 500A • Mounting bolts for cable lugs © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

17. Circuit control using relays • Relays can prove circuit isolation • Control of high currents using a low current circuit • Low resistance low loss & multiple contacts • Catch diode should be fitted across relay coil to prevent coil back e.m.f. from causing damage and interference to other circuits and equipment Two relays shown © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

18. Regular used for Wind & PV • Battery voltage/ charge regulator • System voltages 12-48V • Charge Currents to 20 A • Load currents to 20 A • Measures current and voltage and logs AH for 30 days • Has some control functions eg low volts cut-out, boost charge, generator start etc. © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

19. PV panel connection box • Blocking diode fitted • Wiring protected by conduit • Small amount of wiring slack for ease of termination and removal • Clear PV module instructions • Weather seal fitted conduit Blocking diode © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

20. PV array wiring (large) • Array wiring is protected by fuses • Each string is wired back to this panel • Array broken up into sub-arrays • Commoning terminal strips are used © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

21. Battery terminals • Should be bolted • Use stainless steel bolts, nuts and washers • Use crimp lugs • Have insulating covers (removed in photo) © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT

22. Earth cables • Should be green/yellow stripe • Multi-stranded cable • Building cable earth should be secured under two screws © 2002, 2003 TAFE Qld Renewable Energy Centre BNPIT