Wiring diagrams

The wiring diagram isn’t like the schematic diagram. There are strategic differences in their purposes . . . .

The wiring diagram, or connection drawing, shows an electrician exactly where each wire is supposed to be connected. In contrast, a schematic diagram simplifies the circuit connections to clearly demonstrate a circuit’s functionality.

Schematics don’t contain enough information to show someone how to wire the circuit, and wiring diagrams don’t show how the circuit works.

Schematics usually omit information irrelevant to the function of the circuit, such as the precise physical details of where a group of cables connects. What is shown as a single solid line joining together with a black dot on a schematic diagram may, in reality, be several different cables and wires connected together by jumper wires crossing between different sets of terminal blocks inside of a panel. In other words, schematics are more concerned with electrical characteristics than physical ones.

For this reason, connection drawings are one of the final details to be completed. You should get a head start on them by drafting up preliminary versions as soon as you have enough information to do so, but usually the final document needs to include details like cable and conductor sizes, insulation colors, and conductor and cable numbers. Many of these details are established several steps into the design process, some closer to the end than others.

Just remember this: connection drawings must absolutely be accurate. You don’t have tolerance with wiring errors. You can’t be off by one or two terminal blocks and still have the equipment function properly. In this case, “close” can truly be said to count only in horseshoes and handgrenades.