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What Setting Should You Use to Check Low Voltage? A Simple Guide for Homeowners and Technicians

If you’ve ever needed to troubleshoot a circuit, security camera, or thermostat, you’ve probably asked yourself: “What setting should I use to check low voltage?” Understanding how to test low-voltage circuits safely is an essential skill for anyone working with electrical systems — whether you’re a homeowner, electrician, or low-voltage technician.

In this guide, we’ll break down exactly how to set your multimeter, what voltage ranges to expect, and tips for accurate and safe readings. Our team of experienced low voltage technicians in Los Angeles ensures every connection is properly tested and configured for safety and accuracy.

What Is Low Voltage?

Low voltage refers to electrical systems that operate below standard household power levels. In the U.S., typical household outlets supply 120 volts, while low-voltage systems usually operate at 50 volts or less.

You’ll find low voltage in many everyday systems, including:

  • Doorbells and thermostats (24V AC)
  • CCTV and alarm systems (12V DC)
  • Landscape lighting (12V AC or DC)
  • Network and communication cabling (under 50V DC)

These systems are safer to handle but still require proper tools and knowledge to test accurately.

The Right Multimeter Setting for Low Voltage

To measure low voltage, you’ll need a digital multimeter (DMM) — a handheld device that measures voltage, current, and resistance.

Here’s how to set it up correctly:

  1. Turn your multimeter dial to “V” (voltage)
    • If you’re testing direct current (DC), such as from batteries or CCTV power supplies, select the “V—” or “DCV” setting.
    • If you’re testing alternating current (AC), like doorbells or HVAC transformers, select the “V~” or “ACV” setting.
  2. Choose the correct voltage range
    • Most modern digital multimeters are auto-ranging, meaning they automatically adjust to detect voltage levels.
    • If yours is manual, choose a range slightly higher than the expected voltage (for example, use the 50V or 200V range if testing a 24V or 12V system).
  3. Insert the probes correctly
    • Plug the black probe into the COM (common) port.
    • Plug the red probe into the VΩmA port for voltage readings.
  4. Touch the probes to your circuit
    • Touch the black probe to the negative or ground terminal.
    • Touch the red probe to the positive terminal or wire.
    • Read the voltage value on your display.

Common Low Voltage Readings

Here are typical voltage readings you might encounter:

  • CCTV cameras or LED lighting: 12V DC
  • Doorbells and thermostats: 24V AC
  • Alarm panels: 12V DC
  • Network PoE systems: 48V DC

If your reading is much lower than expected, it could mean a loose connection, voltage drop, or faulty power supply.

Safety Tips When Testing Low Voltage

Even though low voltage is generally safe, precautions still matter. Follow these safety practices:

  • Always use insulated probes and a properly rated multimeter.
  • Never test a circuit if you’re unsure whether it’s high or low voltage.
  • Disconnect power when making wiring changes.
  • Label circuits after testing to prevent confusion later.
  • If readings fluctuate, inspect for corrosion or frayed wires.

Proper testing protects your equipment — and you — from potential damage. If you’re specifically working with lighting circuits, check out our guide on how to test low voltage lighting wire for step-by-step instructions.

Why Accurate Voltage Testing Matters

Accurate voltage readings help ensure your systems perform efficiently and safely. For example:

  • In security camera systems, too low a voltage can cause flickering or signal loss.
  • In HVAC systems, incorrect voltage can prevent thermostats from communicating with furnaces or AC units.
  • In network cabling, power over Ethernet (PoE) relies on consistent voltage to function properly.

By testing with the right settings, you can identify issues early and prevent costly downtime or equipment failure.

Troubleshooting Tips for Low Voltage Issues

If your voltage readings don’t match what you expect:

  • Check your power supply output — it might be delivering less than rated.
  • Inspect cable connections for corrosion or loose terminals.
  • Measure at different points in the circuit to find where voltage drops.
  • Replace damaged cables or connectors to restore full voltage.

Systematic testing saves time and ensures your devices stay powered correctly.

Conclusion

Knowing what setting to use to check low voltage is a small skill that makes a big difference. Always set your multimeter to the correct voltage type (AC or DC), select the proper range, and test safely.

Whether you’re maintaining a CCTV system, thermostat, or lighting network, accurate voltage testing ensures everything works reliably and efficiently. Understanding the purpose of a low voltage test helps ensure accurate readings and safe troubleshooting.

If you’re unsure about your readings or working with complex low-voltage systems, consider hiring a licensed low-voltage technician in your area.