How to Test Low-Voltage Lights

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Low-voltage landscape lights are a popular and attractive way to illuminate your property. Do you need to know how to test low-voltage lights? After all, they sometimes stop working or face other issues, like dimming at the far end of the circuit. To troubleshoot these issues, it is necessary to test the lights and transformer with a multimeter.

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Using a Multimeter

A multimeter is a device that can measure voltage, current, resistance and continuity in electrical circuits. This can help troubleshoot issues with appliances, outlets, lighting and other common household electrical devices.

Multimeters come in two types: analog and digital. Digital multimeters have become very affordable and are sold in home improvement, electrical supply and hobby stores. A multimeter is a good device to have in your arsenal of DIY tools.

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Choosing a Multimeter Port

Multimeters come with several ports into which you connect the measuring leads depending on what you want to measure. To test low-voltage lights, you will need to test both the voltage and the current.

To test the voltage, set the multimeter to a voltage a little above what you expect to be testing. For example, many wall outlets carry 120 volts, so you would set the multimeter to the next-highest step – 200 volts in either AC or DC, whichever type you're testing.

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Then, plug the red testing lead into the port marked "V" (for volts) and the black testing lead into the common port (usually black and labelled "COM"). You will always plug the black lead into this port when using the multimeter. To test low-voltage current, plug the black lead into the common port and the red lead into the port marked "A" (for amps).

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Important Safety Considerations

Always hold the testing leads by the insulated handles. Never touch the metal testing leads themselves. Do not test any current that is higher than your multimeter's rating, which you can find on the multimeter itself or in its instruction manual.

Never ground yourself when testing electrical circuits with the multimeter. Always insulate yourself from the ground with rubber-soled shoes, a rubber mat or another form of insulation. Do not touch exposed metal or pipes, as these may ground you.

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Testing the Low-Voltage Transformer

Your low-voltage lights will be connected to a transformer. This transformer steps down the voltage provided to it so that the output is the correct low voltage for the lights. Before proceeding, visually inspect the transformer for signs of damage or wear.

Transformers can burn out, and this will often show as burn marks or deformation on the transformer. If the transformer is not obviously damaged, you will need to identify its input and output leads. First, check that the input to the transformer is correct by testing the transformer primary in AC mode. If the input is satisfactory, test the output by touching each testing lead to both of the transformer's output leads.

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Then, switch the multimeter's mode to testing current and test the amperage outputted by the device. Consult the transformer manufacturer's instructions to see if the numbers you recorded are in the correct range. If they are not, you can further troubleshoot the transformer, or you can replace it.

Testing the Low-Voltage Lights

If there are no issues with the transformer, check the voltage and current at the lights themselves. The power to the lights can also be affected by the distance from the transformer. There are many different light configurations and ways to adjust each to better distribute the power. Optimal arrangements are usually a "T" shape or hub arrangement rather than a sequential series.

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To test the lights and determine the voltage drop in your circuit, test the voltage and current delivered to the lights, starting from the light closest to the transformer or at the hub and working your way out. To test the voltage delivered to a light, remove the bulb and apply the multimeter's leads to the inside of the bulb's socket. The optimal voltage for this type of outdoor lighting is usually between 12 and 10.8 volts. Test the current at the lead going into the fixture.

If the transformer has been checked and confirmed to be operating properly but the readouts you get at testing the lights are too low, then there is likely a fault in the wiring between the transformer and the lights. If your voltage drop across the light circuit is significant, the simplest solution is to rearrange the lighting circuit such that the distance between the transformer and the outermost light is lessened.

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