When you are dealing with electrical wires, it is important to know which wires are positive and which are negative. Although some cables are clearly marked with plus (positive) and minus (negative) signs, others are not. For unmarked wires, you can first identify the polarity by examining physical characteristics, such as color or texture. If you're still not sure, check the cable with a digital multimeter. After that, turn on the power!
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Method 1 of 2: Identifying Cables in Common Cases
Step 1. Know that the power plug has neither a positive nor a negative side
There is only the "hot" wire and the "neutral" part.
Step 2. Be aware that cables that have “ribs” on extension cables are usually negatively charged cables
If both sides of the wire are the same color-usually copper-the strand that has a grooved texture is the negative wire. Run your finger on the wire to see which one is ribbed.
Feel for another wire with a smooth surface. This is the positive wire
Step 3. Identify the black positive wire on the ceiling light
When you install a chandelier or other ceiling light, first find the 3 wires that come out of the holes in the ceiling where the lights will hang. Note that the black wire is positively charged, the white wire is negative, and the green wire is ground.
Maybe you'll find a copper wire instead of a green wire for ground
Step 4. Be aware that the copper wire in the speaker is usually positively charged
In standard cables used for equipment such as loudspeakers and amplifiers, the silver-colored strand is the negative wire and the copper-colored strand is the positive wire. These wires are often strung together in clear sheaths making it easy to quickly determine their respective polarities.
In Case of Different Cable Color
If the wires are black and red, the black one is the negative wire, whereas the red one is the positive wire.
If both wires are black, but one of the strands has a white line, it means white striped wire is negative, temporary plain black wire is positive.
Step 5. Open the user manual to find out the negative wire on the car
Each car follows its own cable color coding system. There is no standard or international system. So, look for wiring diagrams specific to your make and model in the user manual.
If you no longer have a car user manual, look for it in the library or on the internet. Or, check with a mechanic at your local repair shop or dealer
Method 2 of 2: Using a Digital Multimeter
Step 1. Set the digital multimeter to the direct current voltage setting
Turn the selector switch-that is, the large knob in the middle of the multimeter-to the symbol that looks like a large “V” with a straight line above it. This is the direct current (DC) voltage setting of the multimeter.
Do not use an analog multimeter to check polarity. Connecting the wrong lead (probe or probe) to the wrong wire can damage the analog multimeter
Step 2. Attach 1 lead to each wire to connect it to the multimeter
At this stage, it doesn't matter which lead the wires are connected to. Clip the small alligator clip on the red lead to the end of one wire, and the black one to the other end.
Check that the leads are plugged into the port on the front of the multimeter labeled “COM”. Plug the red lead into the port labeled with the volt symbol, which is "V"
Step 3. Look at the screen to see if the number is positive or negative
After you attach the leads to the cable you want to check, check the numbers on the multimeter display. This is the cable voltage, and the number can be positive or negative.
- If no numbers appear, first check that the alligator clip is firmly attached to the cable.
- If the numbers still don't show up, replace the multimeter battery and try again. If it still doesn't work, chances are you need new leads.
Step 4. Know that the wire attached to the red lead is positive if the number on the multimeter display is positive
If the number on the multimeter turns out to be positive, for example 9, 2, it means that the lead has been affixed correctly. That is, the wire pinched by the red lead is positive and the wire pinched with the black lead is negative.
If the multimeter number is negative, for example -9, 2, it means the lead is reversed, meaning that the wire attached to the red lead is negative
Step 5. Switch the position of the lead and clip the red one to the other wire until it reads a negative number
Open the lead and attach the red lead to the cable previously clamped to the black lead, and vice versa. After swapping, check that the numbers are positive to verify that the leads are attached to the correct wires.
- For example, check if a number that was originally -9, 2 is now 9, 2.
- If the number is still negative, it means the multimeter is faulty. Take it to an electronics repair shop to have the fuse checked, or buy a new multimeter.
Warning
- Reversing the polarity in a circuit can damage the power source, even causing an explosion.
- Connecting the wrong cable-for example, using a positively charged cable when it should be negative-can also burn the wires.
- Never use an analog multimeter if you are not sure which wire is positive and which wire is negative. Attaching the wrong polarity to the wrong leads can damage the multimeter.
