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Difficulty: MediumSwitches and Relays

In an automotive electrical system, an electromechanical relay is installed between a dashboard switch and a high-current cooling fan. What is the primary purpose of using the relay in this circuit configuration?

  1. A
    It acts as a sacrificial protective device that permanently melts open to interrupt excessive circuit current.
  2. It allows a low-current switch to control a high-current load while reducing voltage drop across long wiring runs.Answer
  3. C
    It steps up the source voltage to deliver a higher electromotive force across the fan motor terminals.
  4. D
    It converts direct current from the battery into alternating current before reaching the fan motor.

Answer

The correct answer states that it allows a low-current switch to control a high-current load while reducing voltage drop across long wiring runs.
An electromechanical relay utilizes a low current passing through an internal coil to generate a magnetic field. This magnetic field pulls an armature to close heavy-duty contacts, safely powering high-current loads like cooling fans without subjecting delicate dashboard switches to high current or requiring thick, heavy wiring runs through the passenger compartment.

Step-by-Step Solution

1
Identify the distinct circuit sections established by the relay.
The dashboard switch operates within a low-current control circuit connected to the relay coil, while the cooling fan operates within a separate high-current load circuit connected through the relay contacts.
Relays provide electrical isolation and remote switching between control circuits and power circuits.
2
Evaluate the technical necessity of isolating high-current loads from cabin switches.
Routing substantial current directly through the dashboard switch would require thick gauge wiring into the vehicle interior, cause significant voltage drop over long distances, and degrade manual switch contacts due to arcing.
Electromechanical relays permit small control currents to safely actuate high-amperage contacts placed near the battery and load.
3
Match the identified operational principle to the corresponding functional description.
The relay serves as a remote electromechanical switch allowing low-current input to control high-current output.
Relays do not act as fuses, voltage transformers, or DC-to-AC inverters.

Key Concept

Electromechanical relay function in high-current DC switching
Estimated Time:1m 0s
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Topics

Switches and Relays

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