Reading Electrical Connections

Read the connection convention before tracing a wire

A schematic organizes electrical relationships, not the positions of parts on a bench. Stretching or bending a drawn wire does not change its connections. Moving a line onto a different terminal does.

For the examples on this page, a filled dot at a crossing means the wires join. A crossing with no dot means they do not join. Other drawings may use a bridge or different conventions. Check the legend; an unclear or damaged junction mark is a reason to consult the drawing source.

Count connected conductors, not corners or dots

A node is a set of points joined by ideal conductors. Every point along an uninterrupted wire belongs to the same node, including its bends and branches. A dot marks a connection; it is not a separate component or an extra node.

In the figure, the dotted cross is one node. The undotted cross is two nodes: the horizontal conductor and the vertical conductor. This count concerns the wires drawn in the figure; no connection elsewhere is implied.

Do not trace through a resistor, diode, or open switch as if it were wire. If an ideal switch closes, its two sides become connected; state the switch position before counting nodes. Matching net labels can also indicate a connection without a continuous line across the page. Check the label scope and drawing notes before joining similarly named nets.

Read component identity separately from its value

A reference such as R1 identifies a particular part; a value such as 1 kΩ describes its resistance. D1 can identify a diode or LED, so its symbol and parts information still matter. A ground label identifies a reference or connection according to the drawing; it does not by itself establish a connection to protective earth.

US practice (IEEE 315 / ANSI Y32.2) and international practice (IEC 60617) draw some symbols differently. Use the drawing legend; the forms below are teaching examples, not a claim of compliance with a standard.

Recognize common symbols before tracing their connections

Use the symbol to identify the kind of component, then read its reference and value. The sheet includes both resistor forms and an unpolarized capacitor. A battery is one kind of DC source; other DC supplies may use a circle marked with polarity.

Practice symbol identification

Count four nodes with the switch open, three with it closed

Trace this small component schematic with S1 open. Stop at each component terminal; do not count through the battery, resistor, or LED.

Practice counting schematic nodes