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How to Troubleshoot the Polarity of a DC Wire Circuit

Direct current (DC) wire circuits are usually low voltage circuits drawing electricity from a battery or transformer. These types of circuits are commonly used for railroad and racing car sets. Two wires form the circuit between the power source and the electrical item; the polarity of one is positive and the polarity of the other is negative. The easiest way to troubleshoot the polarity of a DC wire circuit is by using a voltmeter.

Things You'll Need

Voltmeter (or multimeter)

Instructions

- 1
  Locate the terminals on the electrical item wired into the DC circuit. There are two terminals: positive and negative.
- 2
  Turn on the voltmeter. If you are using a multimeter to troubleshoot the DC wire circuit, ensure the dial on the front of the meter is set to read volts.
- 3
  Put the metal prong on the end of the red wire extending from the meter onto one of the terminals on the electrical device. Put the other metal prong on the end of the black wire onto the other terminal.
- 4
  Read the meter. If you get a voltage reading, then the polarity of the wire from the power source connected to the terminal that has the red wire from the meter attached is positive. If there isn̵7;t a reading, then the polarity is likely negative. However, to confirm this, you must continue troubleshooting.
- 5
  Put the red wire from the meter onto the other terminal on the electrical item, and the black wire from the meter onto the terminal that previously had the red wire attached.
- 6
  Read the meter. If you get a reading, then the polarity of the wire connected to the electrical item that has the red wire from the meter attached is positive. The other wire̵7;s polarity is negative. If you still don̵7;t get a reading, then the DC circuit has a wiring fault as no electricity is getting to the electrical item.
- 7
  Check the terminals on the power source using the same method. Whichever of the two wires gives you a voltage reading is the positive polarity wire and the other is negative. If you get a reading, you know the DC circuit has a fault in the wiring, so it̵7;s best to replace the wires. However, if you don̵7;t get a reading, then the power source needs replacing, as no electricity is being produced.

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