They are often red and black, with the red representing the positive lead and the black representing the negative lead. However, this is not always the case; other colors can be used as well.
The color of the wire does not affect how it functions in circuit protection or electrical communication. All wiring should be performed by a qualified electrician, but if you are only required to connect two circuits together then any old piece of wire could be used for this purpose.
Black wire is the safe choice when connecting up live parts of an electrical system. If you're not sure which wire is which, just follow the path of least resistance: if all wires are going into one place, they must be connected to one thing there. You should also try to avoid connecting two live circuits, as this can be very dangerous.
If you are lucky enough to have a trained electrician do your work for you, he or she will know which wires are which and what role each one plays in the system. They will also be able to tell you which type of cable to use where for different purposes. For example, if some cables need to be flexible but others not, then rubber-coated cable is suitable here.
The colors are as follows: Positive: The positive current wire is red. Negative: The negative current wire is black. Ground: If present, the ground wire will be white or grey.
In Australia, red is used for positive on DC and active (or hot, as some call it) on AC. On DC systems, black serves as the negative wire, whereas on AC systems, it serves as the neutral wire. The color green, or green and yellow, is associated with the earth. Any other colors should not be connected to any part of your house wiring.
The easiest way to tell if a wire is red or black is to look at it. If it's red, it's positive; if it's black, it's negative. But what if you can't see it? You might be able to tell by how it's attached to something else. For example, if there's a metal box nearby, then it could be red because it's feeding into that box, or it could be black because it's pulling power away from that box. It's also possible that both wires are black, but more about them in a bit.
Other ways to tell: If one end is marked "R" or has tape over it, then it's the same as red. If both ends have tape over them, then they're both supposed to feed power into one place or another and you shouldn't try to connect them together.
Finally, if you're lucky enough to have two different colored wires inside your wall, then they could be red and black.
On electrical equipment, a black or red-hot wire is commonly connected to a brass-colored screw terminal or a black wire lead. Typically, a white neutral wire connects to a silver-colored termination or white wire lead. The difference between the two is that a hot terminal is not marked with the letter N for neutral; instead it has only one color, usually black or red. A third option for a hot terminal is to use a green terminal; however, these are becoming less common.
A black wire lead is a stripped end of black wire that fits into a metal hole in order to connect an external device to a circuit. Black wire leads are used instead of metal clips because they can be inserted into confined spaces without damaging other wires. Also, black wire leads are more resistant to corrosion than metal clips.
A red-hot wire is a live current carrying conductor at temperatures so high that they would be dangerous to touch if not insulated. With no protective coating to prevent contact with moisture, a person could suffer serious injury or death from this contact. Red means "high temperature" or "burning" and refers to the heat of the metal itself, not its color. Although red hot wires may appear black due to oxidation, they are still considered hot even if they're not burning anymore.
This indicates the wire connected to the red lead is positive, whereas the wire connected to the black lead is negative. If your multimeter displays a negative value, such as -9.2, the leads are inverted, and the red lead is connected to the negative wire. The black lead should be attached to a high voltage source in order for the meter to display any voltage at all.
In general, if you're working with electricity and don't know which way around wires should be attached to provide a path for current, try both ways and see what happens. You might get a spark or a glow from one of the wires but not the other, which would indicate that they need to be reversed.
However, there are some exceptions to this rule. For example, when measuring resistance with a multimeter, you always want both wires attached to something conductive (such as a resistor) because detecting a voltage requires an active circuit (something that conducts when closed but not when open), and an open circuit cannot cause a voltage to appear on the meter. In this case, whichever lead produces a result first is the "positive" lead and can be connected to the conductive object being measured.
Another exception involves connecting two wires together. If you connect two live wires together, it's called a "short", and this could be dangerous.