DC power supplies have a positive and negative terminal, with the positive terminal receiving a positive electrical charge. The polarity relationship is marked by the universal color code and symbol, with correct polarity essential for connecting DC devices to a power supply. Reverse polarity can be used to change device operation, but failure to observe correct polarity can damage devices and power supplies.
The term positive terminal describes which of the two connection terminals on direct current (DC) equipment supplies or is intended to receive a positive electrical charge. DC power supplies always have a positive to negative flow of electrons and always have a negative and a positive terminal. Most DC appliances or machines also have a positive and negative terminal which should always be connected to terminals of the same orientation on the power supply. Failure to do so may cause serious damage to the equipment and power supply. This positive/negative relationship is commonly known as the polarity of a power supply or device.
Any source of direct current electricity flows from a positive source to a negative source. This applies to the DC side of rectified alternating current (AC) supplies, batteries, and solar panel outputs. Each of these DC power sources has a positive terminal and a negative terminal. The permanent relationship between the positive and negative sides of DC power supplies is referred to as the polarity of the power supply. Power supplies and appliances typically also include a ground or ground connection; this however has nothing to do with the power or polarity of the device.
The universal color code and symbol for a positive terminal is red and a plus sign (+). The color code and symbol for a negative terminal is black and a minus sign (-). The polarity relationship, color codes, and symbols for the positive and negative terminals are also used on devices powered by DC power supplies. Connection terminals on power supplies and DC devices will always be marked with one or both of these identifiers. When connecting DC devices to a power supply, it is essential to observe correct polarity. In other words, the positive terminals on the power supply and the device should be connected together with the same being true for the negative terminals.
In some cases, reverse polarity can be used to change the direction of operation of some devices and can be included in controls as a design feature. Some types of resistive DC appliances such as heaters do not have specific polarity requirements and will not have terminal markings. Typically, DC devices are polarity specific; failure to observe correct polarity will result in damage to the device and power supply. This applies to all polarity-dependent DC devices, including speakers, motors, capacitors, and electronic equipment.
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