Node (circuits)

In electrical engineering, a node refers to any point on a circuit that connects two or more circuit elements. In circuit diagrams, these connections are ideal wires with zero resistance, meaning every point on the wire between a set of elements is considered to be the same node.

According to Ohm's law, V = IR, the voltage across any two points of a node (with zero resistance) is

$V=IR=I\cdot 0=0,$

showing that the voltage at any point of a node is the same.

Each different color in circuit above is a different node

In this circuit diagram the voltage in the green node is the same throughout, likewise, the voltages in the blue node and the red node are the same throughout.

In most cases, the voltage difference between one point on a piece of metal (such as a copper wire), and the voltage at another point of the same piece of metal or on other bits of metal with metal-to-metal contact with the first piece of metal, is so small that it is usually considered insignificant. So every bit of that connected metal can be considered part of the same node.

Some notable exceptions, where the voltage difference is large enough to become significant, include:

• high-precision resistance measurements using a Kelvin connection
• the difference in voltage between ground and neutral, between the "neutral wire" and the "safety ground in a domestic AC power plugs and sockets, can be fatal. A properly installed electrical system connects them together at one (and only one) location, leading many people to the fatally incorrect conclusion that they are at "the same" voltage, or that the safety ground is "redundant and unnecessary".
• the Seebeck effect and the Peltier effect
• joints involving aluminium wire

Dots used to mark nodes on a circuit diagram are sometimes referred to as meatballs.