Is Black Negative or Positive: How to Identify the Polarity of an Electrical Wire?

Is black negative or positive? This is a question you will always consider when doing an electrical installation. It helps you determine the polarity. However, it can be challenging to clearly distinguish the difference between the wires.

You need more than the wire color to differentiate wire polarities without difficulty or unnecessary accidents.

Color can mean different things depending on the type of power you are handling. Sounds confusing?

Don’t worry. This article will help you clear any confusion and provide a clear insight into everything you need to know to identify the polarity of an electric wire. 

What is Electrical Polarity?

Simply put, polarity is the existence of a body in either a positive or negative state.

A negative polarity occurs when a body has more electrons with a negative charge. On the other hand, positive polarity occurs when a body has more protons. 

As subtle as the subject could be, polarity is essential in connecting polarity-dependent devices. A good example is batteries, electrical machines and measuring meters.

Additionally, polarity helps indicate the flow of the current as current flows from the positive to negative terminals in power sources while current flows from the negative to the positive terminals in other elements, such as resistors.

Batteries with electrical polarity

Batteries with electrical polarity

Why Reversed Polarity is Dangerous

Usually, a reverse polarity occurs when you wire the hot and neutral wires on an outlet in opposite directions. In many cases, the hot wire or live wires are usually black. On the other hand, the neutral wire is ordinarily white.

A reverse connection occurs when the two wires become interconnected, affecting the directional flow or the electric current.

The following are some of the possible dangers of reverse polarity connections:

Increase Chance of an Electric Shock

open and closed switches with normal polarity

Caption: open and closed switches with normal polarity

In some circumstances, a reverse polarity outlet increases the case of a shock hazard. To illustrate the potential of an electric shock, please see the two illustrations, which show a correctly wired circuit with a correct polarity arrangement.

When switched on, the circuit allows current to flow through the switch to the bulb. Therefore, removing the bulb without fear of 120 V is present without turning off the switch. The switch thus cuts the power supply to the bulb as it creates an open switch.

However, in a reversed polarity setup, when you turn on the switch, the current flows through the bulb before reaching the switch. Therefore, you will likely experience an electric shock even when you turn off the switch. 

It is thus vital to ensure you have the correct polarity wiring. It is, however, recommended that you unplug your device from the power receptacle when done using it.

Increased Cases of Fire Accidents

A reversed circuit can quickly start a spark caused by current flow. No matter how small the spark may be, it will likely start a fire, especially with other ingredients such as sufficient fuel, oxygen and temperature.

Damage to Electrical Equipment

It’s always important to check your electrical equipment’s color-coded to ensure you get everything correctly. Switching wires can easily ruin, toast or blow up your equipment.

To illustrate, think of the electrical system of your car. If you reverse the terminals of the cable connection, you will cause the system to experience an unexpected power surge.

As a result, you are likely to damage the sensitive electronic components, which may include but are not limited to the alternators, the starter motors, fuses, circuit breakers and even the engine control module.

Indeed, some electrical components, such as speakers, are not affected by changes in polarity. Try to change the terminal connections, and your speaker will still work. 

However, if you increase the number of speakers, they will need a constant polarity connection. The quality of music you get when you reverse connect your circuit is a current flow that affects the frequency.

The changes in polarity cause the cancellation of phases. As a result, your course cancels some types of frequencies.

Any sound produced that falls somewhere in between the frequency is not audible.

You may notice that your speaker has audio keeps breaking at some point. In other cases, you may notice abrupt interruptions during your audio streaming sessions. 

The good news is that a polarity change does not mean you have a broken speaker. As a result, it can resume its normal operations when you connect the polarities correctly.

Is the black Wire Positive or Negative?

Electrical wire colors

Caption: Electrical wire colors

Defining a black wire as positive or negative it’s not always easy. The type of circuit you have will determine the polarity of the wire used. Therefore, you may find the contradictory meaning of a black wire in many cases. 

The following are circuits and circumstances where the black wire may have a different polarity.

Wire Colors for DC Power

In the case of a DC (direct current) power supply, a red cable is a positive terminal. On the other hand, the black wire represents the negative terminal.

The white wire is the neutral cable. In a DC circuit, current flows in one direction at all times.

In cases where both wires are black, look for strips to determine their polarity. The positive wire has a white stripe, while the negative wire is plain black.

Wire Colors for AC Power

An AC power changes direction after every phase of the current flow. The current may be in three or more phases. The black wire is the phase 1 hot wire in such a case.

It, therefore, qualifies to be the positive wire.

On the other hand, the red wire is the phase 2 hotwire and, thus, the negative terminal. The blue wire is the phase three hotwire, while the green is neutral. The white wire always acts as the neutral wire.

Speaker Wiring

In a speaker system, the copper wire is the positive terminal. On the other hand, the silver strand is the negative wire.

Even though hidden, you can easily identify their terminals by looking at the exposed wiring.

Appliance Plugs or Power Cords

A power cord will have hot (neutral) wires rather than positive or negative polarities.

The longer prong connects to the neutral wire terminal in the latest 2-strand appliance codes with two prong plugs. 

You may also identify the neutral wire as white stripe, ribbing or white insulation. You will also notice the live wire as one without ribbing or stripe, possibly black or red.

On the other hand, the green wire, which is not common in appliances, is the ground wire.

Extension Cords 

In an extension, the grooved textured wire is the negative wire. On the other hand, the smooth is the positive.

You can use your fingers to feel the smooth texture of the wire. It is thus easy to determine the polarity of cables in an extension code.

How to Test Red or Black Wires/Cables for Their Polarity

Test red or black wires

Caption: Test red or black wires

A Multimeter can help you quickly determine the polarity of cables. The following are two crucial ways you can use it to test red or black wire’s polarity. 

Using Resistance

To achieve correct measurements, use an auto-ranging multimeter. First, tune your multimeter to the ohmmeter. Connect the black probe to the ground port, such as metal. Next, connect the red probe to the red cable.

An infinity reading means that the connection is not complete. On the other hand, a reading of zero means that the red cable is the negative terminal.

Using Voltage

To use voltage testing, set your multimeter to DC voltage mode. Connect the red probe to the red cable. If you notice a positive value, the cable is a positive wire.


So now you know the answer to the question, “Is black negative or positive?” Usually, the black wire will be negative if you have a DC.

And in an AC, the black wire is the positive terminal. In many cases, though, red is not always positive. We hope you now understand wire polarity better.

You can always refer to the schematic diagram to determine the polarity of respective wires before carrying out any installation or repair work.