Glossary of residential electrical design terms

Short definitions of the terms that appear in residential electrical drawings, as we use them in the deliverables.

Base drawing (architect's DWG)

The architect's floor plan in DWG, the data structure the whole electrical set is built on. Its quality — closed rooms, layers separated by role, room names as text — decides how much of the work can be derived rather than drawn by hand.

Single-line diagram

A one-line drawing of a distribution board: the incoming supply, the main switch, and every final circuit with its breaker, cable and load. In a consistent set it is not drawn separately but derived from the circuit list.

Block diagram

The overview of how power is distributed through the building: apartment boards feeding into floor boards, floor boards into the main distribution board. It shows the tree, not the individual circuits.

Distribution board

The enclosure that houses the breakers and residual current devices for a set of circuits. A residential building has apartment boards, floor boards and a main board (MDB); larger sites add sub-boards (SMDB).

Final circuit

A single protected run from a board to the outlets or fixtures it serves — for example one lighting circuit or one socket circuit. Every point on the plan carries the identifier of the circuit it belongs to.

Circuit numbering

The fixed naming scheme for circuits — board, unit, type, sequence number. Which convention is chosen matters less than never departing from it: consistent numbering is what lets the single-line diagram be a consequence of the plan.

Connected load (installed power)

The sum of the power of everything connected on a circuit, a board or the whole building, before any diversity is applied. It is counted from the equipment on the plan, not estimated per square metre.

Diversity factor

The factor that reduces the connected load to a realistic maximum demand, because not everything runs at once. For residential buildings it usually comes from the network operator's connection conditions.

Maximum demand

The realistic peak load a supply must be sized for, after the diversity factor is applied to the connected load. It determines the incoming service and the size of the main protective device.

Voltage drop

The loss of voltage along a cable under load, expressed as a percentage. Each circuit is checked cumulatively against a limit so that the far end of the run still has usable voltage.

Cable cross-section

The conductor size in square millimetres, chosen by the circuit's current, its protective device and the voltage-drop check. Cables are summed by cross-section in the bill of quantities, because a socket and a light do not use the same cable.

Circuit breaker (MCB)

The automatic device that disconnects a circuit on overload or short circuit. Its rating and tripping curve are chosen from the circuit's role and current, coordinated with the cable it protects.

Residual current device (RCD)

The protective device that disconnects on earth-leakage current, guarding against electric shock. In residential installations it typically covers socket and wet-room circuits at 30 mA.

Riser (vertical)

The vertical run that carries feeders between floors through the building's shafts. Its route has to be checked against the structure early: a riser that meets a beam is a design problem, not a drafting detail.

Socket outlet

A point where a plug connects to a circuit. Its position follows the intended furniture — the worktop, the two sides of the bed, the TV wall — not a constant pitch along the wall.

Two-way switch

A switch that controls the same light from two points, used at the two ends of a corridor or a staircase. A third control point needs an intermediate switch. Switching follows how people move through the home.

Connection conditions

The requirements the network operator sets for connecting a building — the contracted power per meter, the diversity factors, the metering arrangement. They are an input to the design, not something the drafting decides.

Bill of quantities

The list of everything to buy and install, with description, unit and quantity. When every symbol on the drawing carries its own line, the bill is counted from the drawing rather than typed, and stays aligned through revisions.

How these terms fit into the method: The method · Sample project