Extra-Low Voltage Switching (0-30V)

Question 1

What is the difference between an ELV switching relay and a standard relay?

Answer 1

• An ELV switch contains a mechanical latch and a soft iron core within two separate coils, to facilitate for two positions of the core and contacts.
• A standard relay has a fixed core to magnetically pull an armature which changes the connections in a circuit.

Question 2

ELV relay switches are “_____” switches.

Answer 2

Momentary.

Question 3

What is considered extra low voltage?

Answer 3

Up to and including 30 Volts.

Question 4

What are three advantages to using ELV switching?

Answer 4

1. All control circuit components need only be rated for ELV.
2. All control wiring can be small gauge due to a small current.
3. Fewer overall power losses because fewer high current conductors are used.
4. System can be less costly and more versatile than line voltage switching.
5. Several switches can operate one relay
6. One switch can operate several relays.

Question 5

How many diodes are used in a GE 3 wire ELV switching system?

Answer 5

1 as a rectifier so that holding the initiating switch does not cause relay coil waffling from the AC supply.

Question 6

How many diodes are used in a Douglas 2 wire ELV switching system?

Answer 6

4 to control direction of electrons through the relay coil, reversing direction of the field established by the coil, when respective buttons are pressed.

Question 7

In a 3 wire ELV switching system when using a switch with a pilot light, how many terminals will the switch have ?

Answer 7

4 terminal switch, complete with a 5 terminal relay.

Question 8

In addition to manual operation, what other means could activate an ELV switch?

Answer 8

Automatic switching.

• Input from:
  
  • photocells
  • Motion sensing devices
  • Magnetic reed switches
  • Limit switches
  • Etc…