Extra-Low Voltage Switching (0 - 30 V) 030104g Flashcards
How do extra-low voltage relays differ from standard relays?
Objective 1 Page 3
Relay is only momentarily energized for both on and off functions. Relay contacts mechanical latch.
What is the function of a relay in an extra-low voltage switching system?
Objective 1 Page 2
Allows a lower voltage control circuit to switch a higher voltage power circuit.
What are the six advantages of an extra-low voltage switching circuit?
Objective 2 Page 5 & 6
1) All control circuit wiring, switches and relays must be rated only for extra-low voltage.
2) They require only small gauge control wires compared to the larger wires used for power circuit loads.
3) There are fewer power losses in the control circuit wires.
4) The system can be less costly and more versatile than line voltage switching.
5) Several extra-low voltage switches can operate one relay, which eliminates the need for 3 way and 4 way switches.
6) A single extra-low voltage switch can control several relays, switching several circuits at one.
What separates the extra-low voltage control circuit from the line voltage power circuit?
Objective 3 Page 9
A metal barrier. (Required by the CE code)
What are the two types of extra-low voltage switching systems?
Objective 3 Page 8
Three-wire relays with three-wire switches.
Two-wire relays with two-wire switches.
What is a rectifying diode used for?
Objective 3 Page 10
Allows pulses of current to flow to the coil in one direction only (changes the ac to dc current). Provides protection for the relay if the momentary contact switch is stuck or held in the on or off position.
Why are pilot lights used for in extra-low voltage switches?
Objective 3 Page 13
Usually an LED that illuminates to show that a circuit is energized. Generally used when the switch is not located in the same room as the fixture.
If a switch with a pilot light is used in a three-wire relay system, how many wires must the switch and relay each have?
Objective 3 Page 14
4 wires for the switch
5 wires for the relay
Does a two-wire relay system require a special relay when the switch has a pilot light?
Objective 3 Page 17
No. Electronic devices within the switch can provide LED pilot light indications.
