Buzz
When working with electrical wires, it’s important to recognize the polarity of each wire. Some wires are clearly marked with a plus sign (positive) or a minus sign (negative), while others are not. For unmarked wires, you can start by inspecting physical traits like color or texture. If you’re still unsure, use a digital multimeter to check. Once you’ve identified the polarity, you can proceed with your work.
Steps
Identifying Wires in Common Situations
It’s important to note that the plugs of electrical devices don’t actually have positive and negative poles. Instead, they are referred to as ‘hot’ and ‘neutral’ (or cold).
For extension cords, the wire with ridges is typically the negative wire. If you're looking at a cord with two strands of the same color (usually copper), the one with grooves is the negative wire. Run your finger along the wire to feel which one has the ridges.
- If the other strand is smooth, then it’s the positive wire.
The positive wire is black for ceiling-mounted light fixtures. When installing chandeliers or any type of recessed lighting, first look for the three wires protruding from the hole to connect the light. If there's a black wire, it's positive, a white wire is negative, and a green wire is for grounding.
- Sometimes the ground wire may be copper instead of green.
In speaker wire systems, copper-colored wire usually carries the positive polarity. For standard wires in devices like speakers and amplifiers, the silver wire is negative, while the copper wire is positive. These wires are often secured together by clear insulation, making it easy to quickly identify the polarity of each wire.
Other scenarios
For wires with multiple colors, including red and black, the black wire is negative and the red wire is positive.
If both wires are black but one has a white stripe, the striped wire is negative and the solid black wire is positive.
Refer to the user manual to identify the polarity for the car wiring system. Since there is no international standard or system, each car has its own color code for electrical wires. You’ll need to check the wiring diagram for your specific car model and brand in the user manual.
- If you no longer have the manual, you can search for it in a library or online. You may also contact a technician at a local dealership or shop.
Using a Digital Multimeter
Set the digital multimeter to measure direct current (DC) voltage. Turn the large selector knob in the center of the multimeter to the symbol that resembles a capital ‘V’ with a minus sign above it. This setting is for measuring DC voltage with the multimeter.
- Do not use an analog multimeter for polarity testing, as it could be damaged if you connect the leads incorrectly.
Connect one probe of the multimeter to one end of the wire. It doesn't matter which probe connects to which wire. Use the alligator clips to secure one probe (red and black) to one end of the wire.
- Ensure the black probe is plugged into the 'COM' port on the front of the multimeter. The red probe should be connected to the port marked with the voltage symbol ('V').
Check if the reading is positive or negative. After connecting the probes to both ends of the wire, observe the result displayed on the multimeter screen. This reading represents the voltage of the wire and may appear as either a positive or negative number.
- If there's no reading, check if the alligator clips are securely attached to the wire ends.
- If the reading still doesn’t appear, try replacing the multimeter battery and test again. It’s possible the probes are faulty, in which case, you’ll need to purchase new ones.
If the display shows a positive number, the wire the red probe is connected to has a positive polarity. If the multimeter shows a positive reading (e.g., 9.2), it means the probes are connected correctly. This indicates that the wire the red probe is attached to is positive, while the wire the black probe is touching is negative.
- If the multimeter shows a negative number (e.g., -9.2), it means the probes are connected in reverse, and the wire the red probe is touching is negative.
Swap the positions of the probes if you get a negative reading. To do this, attach the red probe to the wire where the black probe was connected and vice versa. After swapping the positions, if the display shows a positive reading, it means the probes are now properly connected to the correct wires.
- For example, if the previous reading was -9.2, it will change to 9.2 after swapping.
- If the display still shows a negative value, the multimeter might be faulty. You can take it to an electronics store to check the fuse or purchase a new multimeter.
Warning
- Reversing the polarity in a circuit can damage the power source or even cause a fire or explosion.
- If you connect the wrong wire (e.g., using the positive wire when you should use the negative one), the wire could catch fire.
- Never use an analog multimeter if you are uncertain about the wire's polarity. Incorrectly connecting the probes can damage the multimeter.
