Electrical drawing symbols

Switch symbols show where each switch sits on the wall. The light or load it controls is usually tied back to it with a dashed switching line, so follow the line rather than assuming the nearest light. Two way switches come in pairs for stairs and long halls, with an intermediate switch between them when there are three or more control points. Mounting height is normally given in the drawing notes or legend, not on the symbol.

Lighting symbols mark the outlet position on the ceiling or wall, not the exact fitting. The fitting itself usually comes from a luminaire schedule, keyed by a letter or number next to the symbol. Fluorescent symbols show the number of tubes, which tells you the fitting size when you rough in. Emergency and exit lighting is often drawn with its own symbols on a separate layer, so check the legend before you count fittings for a quote.

Socket outlet symbols show the number of outlets at each point and whether they are single or multiple. Dedicated circuits for appliances such as ovens, dishwashers or air conditioners are usually noted in text beside the symbol. Telecommunications outlets look similar to power outlets on some plans but are data cabling, which in Australia must be installed by a registered cabler.

These symbols mark the switchboard (distribution centre), the point where the supply enters the installation (the consumer's terminal), and junction or connection boxes. Plans rarely show every cable route; they show where things start and finish, and the electrician works out the run on site. Check the legend for whether a box is accessible, because junction boxes generally need to stay reachable.

System and tap-off outlets belong to a distributed signal system, typically TV antenna or MATV wiring in a building. A looped outlet passes the signal on to the next point, so the order of outlets on the plan matters. These are signal outlets, not power, though a power outlet is normally needed nearby for the equipment that plugs into them.

Fixed appliances such as ceiling fans and water heaters get their own symbols because each needs its own supply arrangement. A water heater usually means a dedicated circuit, often on off-peak control, and a ceiling fan needs a fixing point and usually its own switch or controller. Check the drawing notes for the appliance rating so you can size the circuit.

Building symbols show the construction you are working in. Wall type tells you how cables can be run: a timber stud wall is easy to fish through, cavity brick and brick veneer need more planning. Door swings matter for switch placement, because switches belong on the latch side so they are reachable as the door opens.