Proper knowledge of electrical wiring and connections is crucial while installing, repairing, or maintaining a device or equipment. We have been using the colors of wires as a visual indicator to identify their functionality, polarity, etc. for a long time. But still, several people have a confusion regarding the importance of color. One common question that many beginners or novices to automobiles, electrical, or electronics have is regarding the polarity of red and black wires. Is red positive or negative? Spoiler alert! In most applications, Red is usually positive and Black is negative.
In this guide, we will understand the importance of wire colors and give a comprehensive answer to the question “is red positive or negative?”.
Is Red Positive or Negative?
Let us take three electrical scenarios and explore them. In the process, we will see how to identify the positive and negative wires very easily.
1. In Car Battery
If you have a dead or flat car battery or you have a very old one that needs to be replaced, then you will ask the question “is red positive or negative”.
The car battery is responsible for starting or cranking your car engine and also provides energy for ignition as well as the lighting system. If you haven’t started the car for a few days, the battery discharges significantly and you will have a hard time starting the car.
You can deal with this situation in a couple of ways. You can jumpstart your car with another car or you can recharge the battery. In either case, you have to identify the positive and negative terminals of the battery and their corresponding wires.
2. To Jumpstart the Car
If you open the hood of your car and take a look at the battery terminals, you will notice that the positive terminal (which is marked with the symbol ‘+’) is connected to a Red Cable and the negative terminal (which is marked with the symbol ‘-’) is connected to a Black Cable.
So, in cars (or all automobiles in general), the red wire or cable is usually positive and the black wire is negative.
With this information, you can jumpstart by connecting red and black jumper cables between the two cars. The sequence in which you connect the cables is very important.
This is usually associated with the polarity of the battery terminals rather than the colors of the cables. But as red is positive and black is negative, we usually provide instructions using these colors so that even beginners can do the job very easily without worrying about the polarity of the terminals.
That said, we recommend all car owners remember red wire and the corresponding terminal are always positive and black wire and the corresponding terminal are always negative.
3. To Charge the Car Battery
The same applies while charging the battery as well. If you take a look at some popular battery chargers in the market (or if you already own one), you can notice that it comes with two cables with alligator clips.
As expected, the colors are these cables are red and black. Even in this case, the red cable is positive and the black cable is negative.
So, while charging the battery, you have to connect the red alligator clip to the positive terminal and the black alligator clip to the negative terminal of the battery.
4. To Replace the Car Battery
Another common problem is if the car battery is old (the average life of a typical flooded lead acid SLI battery is 4 to 5 years). In this case, the battery cannot hold the charge and you have to replace it.
In this situation, you have to disconnect the red and black wires in a sequence while removing the old battery (remove the black or negative wire first and then remove the red or positive wire).
After taking out the old battery and placing the new battery, you have to connect the red and black cables in the reverse order i.e., first connect the red cable and then connect the black cable.
5. In DC Electronics
If you work with DC Power Supplies for LEDs, Solar, Batteries, DIY Projects, Microcontroller-related stuff, etc., then you know that in the world of DC, we only deal with two polarities; positive and negative.
The Positive voltage is usually a number greater than 0V. Some common positive voltage levels are 3.3V, 5V, 12V, etc. In the case of the negative potential, it is usually 0V and is simply known as ground.
As a rule of thumb, in DC Electronics, Red is always positive and Black is always negative. If you look at the wires of a USB cable, be it a regular USB-A Cable or the modern USB-C Cable, you will notice that the red cable carries VCC or the positive of the power supply while the black cable is the ground (which is 0V).
6. In AC Mains
Things are slightly different when it comes to the AC Main color codes. Here, we don’t have the concept of positive and negative but rather the terminals (or corresponding cables) are live (or hot) and neutral.
The color codes of AC Mains wiring are highly region specific. For instance, in the U.S., the single-phase connection has three wires in the form one hot, one neutral, and one ground.
In this type of connection, Black wire acts as the Hot, White wire acts as the Neutral (sometimes even gray wire acts as neutral), and a Green wire or bare Copper wire acts as the grounding cable.
If the service comes with two hot wires (two phases), then the phase 1 (the first hot or live) wire is Black while the phase 2 (the second hot or live) wire can be either Black or Red.
In a three-phase system, the phase 3 (the third hot or live) wire is Blue.
This color scheme is not applicable in other countries. For instance, in the UK, the colors for hot, neutral, and ground are Brown, Blue, and Green/Yellow stripes respectively.
We made a dedicated guide on Electrical Wiring Color Codes. Do check that guide for more information on the colors of conductors in different regions.
How to Test Red or Black Wires/Cables For Their Polarity?
From the above discussion, it is clear that Red is usually positive and Black is usually negative in the case of automobiles and DC Power Systems. Is this always the case?
No. Most engineers and designers follow these color codes and we also recommend you follow the same. But there are no rules regarding the usage of specific colors for positive and negative polarities.
If this is the case, then how to check if red is positive or negative? We can easily check the polarity of the red or any cable in cars, bikes, or DC Electronics with the help of a multimeter.
We will see the procedure in cars and using this method, you can do a similar test in other scenarios as well (DC Power Systems).
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Using Resistance
For the purpose of this test, we recommend an auto-ranging multimeter. You don’t have to get a crazy expensive multimeter from Fluke or other popular brands. Any decent and inexpensive multimeter would be fine.
But we do not recommend the $5 multimeter. They are absolute garbage. Look for Uni-T, Kaiweets, Aneng, or other similar low-price but good multimeters.
Speaking of multimeters, you will notice it has two probes, where one is Red and the other is Black. So, is red positive or negative in a multimeter? As the multimeter is a DC device, Red is always positive and Black is always the ground probe (which is usually 0V).
That said, take the multimeter, and set the meter to Ohmmeter i.e., to test the resistance. Now, connect the black probe to any ground port on the car. Any metal part in the engine bay that doesn’t have any paint is a ground point in the car.
Then take the red probe and connect it to the red cable of the battery. Usually, the red cable has a protective cover so that it doesn’t come in contact with any ground points. So, in order to connect the red probe to the red cable, you have to remove the cover.
After connecting the probe, look at the multimeter. You will get either ‘0’ or a very high value (or infinity). If the value is very high or open circuit, it means there is no connection between the red cable and the ground points.
From this, we can conclude that red is positive. But if the value on the multimeter is ‘0’, then it means there is continuity between the red cable and the ground. In this case, the red wire is negative.
But the chances of red wire being negative in a car (or any other automobile) is very rare.
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Using Voltage
You can also test the voltage between the red and black cables (or ground points) in a car and determine if red is positive or negative. For this, set the multimeter for DC Voltage mode.
After this, connect the black probe of the multimeter to any ground point on the car. Then take the red probe and connect it to the red cable of the car battery.
If you get a positive voltage value on the multimeter, then the red cable is positive. On the other hand, if you get a negative voltage reading on the multimeter, then the red cable is negative.
Again, the chances of red cable being negative in a car are slim to none. But this is just the procedure you can follow to determine the polarity of the red and/or black cables in any system.
Conclusion
If you are working with a car battery or any car electrical system, you will face a bunch of wires. But the two common colors are red and black, which usually carry power.
A common question many beginners have regarding the colors of wire in a car is “is red positive or negative?”.
Apart from cars, we often use red and black colored wires and cables in DC Electrical and Electronics systems i.e., systems that use DC Power Supply. Some examples of such systems are LEDs, Solar, Microcontroller DIY Projects, etc.
In this guide, we looked at different cases where we often use red and black wires and gave an answer to the question “is red positive or negative?”. Most of the time, red is always positive, and black is always negative.
After that, we also saw how to test whether red (or any cable for that matter) wire is positive or negative in a car. You can use the same method in other systems and determine the polarity of the wire.
We hope that this guide could help you in understanding the common implementation of red and black cables. If you feel we missed something or want us to add anything, do let us know in the comments section. It will not only help us but also other readers as well.
