Residential electrical design
A home installation is not improvised: it is designed. The regulations define how many circuits are needed, what can hang from each one and how it is protected, and that design is what is later drawn, built and tested.
Conductor sizing, overcurrent protection, the residual-current device (RCD) and grounding are developed in electrical installations, and the protection devices are revisited in depth in electrical protection. Here the work is the design: how many circuits, of what type, with what demand, and how it is documented.
01Electrification grades
The first step is to classify the dwelling. The AEA (Argentine Electrotechnical Association) regulations set four grades according to floor area and expected demand, and from that grade comes the minimum number of circuits.
| Grade | Floor area | Demand | Minimum circuits |
|---|---|---|---|
| Minimum | up to 60 m² | up to 3.7 kVA | 2 |
| Medium | up to 130 m² | up to 7 kVA | 3 |
| High | up to 200 m² | up to 11 kVA | 5 |
| Superior | over 200 m² | over 11 kVA | per design |
Meeting the minimum grade is what the regulations require, but a sensible design anticipates: a spare circuit in the distribution board, an empty conduit up to the ceiling, a cross-section one step larger in the feeder. All of that costs little during construction and a great deal afterwards.
02Circuit types
| Code | What it supplies | Max. points | Cross-section | Protection |
|---|---|---|---|---|
| IUG | General-purpose lighting. | 15 | 1.5 mm² | 10 A |
| TUG | General-purpose outlets. | 15 | 2.5 mm² | 16 or 20 A |
| IUE | Special-purpose lighting: larger loads or outdoor lighting. | 12 | 2.5 mm² | 16 A |
| TUE | Special-purpose outlets: water heater, oven, washing machine. | 12 | 2.5 mm² or more | 20 A |
| ACU | One air-conditioning unit per circuit. | 1 | per unit | per unit |
| ATE | Feeder to a sub-distribution board. | — | per calculation | per calculation |
| APM | Feeder to small motors: pump, gate. | — | per motor | per motor |
- Lighting and outlets never share a circuit: if the protection trips because of an appliance, the house is not left in the dark.
- Every outlet circuit carries a 30 mA RCD.
- Every circuit carries its protective conductor, green and yellow, to every point.
- Large loads go on their own circuit: they are not hung from a TUG.
- Line (live): brown, black or red.
- Neutral: light blue.
- Protective (PE): green and yellow, and only for that use.
It is not a decorative convention: it is what allows another technician to work on the installation years later without guessing. Using green-yellow as a live conductor is a serious violation.
03Distribution boards and raceways
| Element | Design criteria |
|---|---|
| Main distribution board | Main switch, RCD, one thermal-magnetic breaker per circuit, and separate neutral and ground terminal blocks. With spare room, and at an accessible height: between 1.4 and 1.8 m. |
| Sub-distribution board | When there is a remote area or a differentiated use —outdoor barbecue area, workshop, upper floor—. It is fed by an ATE circuit. |
| Raceways | Semi-heavy steel conduit or rigid PVC conduit embedded in the wall, cable tray or surface trunking in view. They are sized so that the conductors fill at most one third of the cross-section. |
| Boxes | Rectangular for switches and outlets, octagonal for ceiling points. Every splice goes inside an accessible box, never buried in the wall. |
| Identification | Each protection device labeled with the circuit it supplies, and the single-line diagram attached to the door of the board. |
- Splices without a box, twisted together and taped, inside the wall or the ceiling.
- Using the protective conductor as a neutral, or connecting neutral and ground downstream of the distribution board.
- Hanging the water heater or the air conditioner from a general-purpose outlet circuit.
- Connecting the grounding to a water pipe: today pipes are plastic and do not conduct, and even if they did conduct, it is not a valid ground electrode.
- Working without verifying the absence of voltage, even when “the breaker is already off.”
04Low-current and extra-low-voltage systems
The design does not end with power. The same building also houses the data network, the intercom, the alarm, the doorbell, TV and home automation, all at extra-low voltage.
Low-current systems run in their own conduits. Sharing a conduit with power induces noise in the data and, above all, no longer guarantees insulation between systems.
An empty conduit with a pull wire to every room, and a space in the communications board. It is cheap during construction and impossible afterwards.
Safety extra-low voltage —up to 50 V AC— supplies doorbells, intercoms and control: it is not dangerous to touch, but it still demands neat work.
05Project documentation
| Document | What it shows |
|---|---|
| Floor plan | The actual location of points, switches, outlets, boards and raceways on the architectural drawing, with standard symbols. |
| Single-line diagram | The complete board on a single line: main switch, RCD, each thermal-magnetic breaker with its circuit, cross-section and protection. |
| Functional diagram | How one particular circuit works: a staircase point, an automation, a two-way switching arrangement. |
| Load schedule | Circuit by circuit: number of points, expected power, simultaneity factor, current and voltage drop. |
| Design calculations | How each cross-section and each protection device was arrived at. It is what allows the design to be reviewed without redoing it. |
The drawing is made with the tools and symbols covered in technical drawing and CAD and component symbols.
06In the lab
On each student’s own floor plan: count rooms and areas, determine the electrification grade, define the circuits with their points and put together the load schedule. Calculate the maximum simultaneous demand and check that the chosen grade covers it.
Draw the complete single-line diagram of the designed board, with each protection device labeled, its rated current, the conductor cross-section and the circuit it supplies. Review it with peers looking for mistakes: it is the fastest way to learn to read them.
Physically assemble the designed board on a panel: DIN rail, main switch, RCD, thermal-magnetic breakers, neutral and ground terminal blocks, wire dressing and labeling. Verify continuity and the absence of crossed wires before energizing.
On the practice installation: measure insulation resistance, verify the continuity of the protective conductor at every point, test the RCD with the test button and with an instrument, and measure the grounding resistance. Document everything in a test report.
07Common mistakes
| Mistake | Consequence |
|---|---|
| A single circuit for the whole house | Any fault leaves everything without power, and the conductor works at its limit. |
| Lighting and outlets mixed | When the protection trips because of an appliance, you are left in the dark at the worst moment. |
| More points than allowed per circuit | The conductor is overloaded and the protection does not warn in time. |
| Water heater or air conditioner on a TUG | Permanent overload of the circuit and of the plug, which ends up heating and melting. |
| No protective conductor to the point | The RCD cannot act as expected and the casing of an appliance can become live. |
| Unlabeled board | Every later intervention is done blind, by trial: it is dangerous and slow. |
| Data and power in the same conduit | Noise in the data network and loss of separation between systems. |
| No spare room in the board | The first expansion forces replacing the entire board. |
08Self-assessment
What defines the electrification grade of a dwelling?
The floor area and the expected demand. The grade gives the minimum number of circuits: 2 for minimum, 3 for medium, 5 for high, and per design for superior.
Why are lighting and outlets not mixed?
Because a fault in an appliance would trip the protection and leave the dwelling in the dark, just when you need to see to solve the problem.
What is the minimum cross-section of a lighting circuit and of an outlet circuit?
1.5 mm² for general-purpose lighting and 2.5 mm² for general-purpose outlets.
What is the maximum simultaneous power demand?
The sum of the expected loads multiplied by their simultaneity factors, because not all loads run at the same time. It is what is used to size the feeder and choose the grade.
Which circuit corresponds to an air-conditioning unit?
Its own ACU circuit, one per unit, with its protection sized according to the unit. It is never hung from a general-purpose outlet circuit.
What color corresponds to the protective conductor, and what other use can it have?
Green and yellow, and no other use. That color is reserved exclusively for the protective conductor.
Where are splices made?
Always inside an accessible box. A splice embedded in the wall or hidden in the ceiling is a fault waiting to happen, and impossible to find besides.
What documents make up the design?
Floor plan, single-line diagram, functional diagrams, load schedule and design calculations. Without them there is an installation, but not a design.
Why do low-current systems run in separate conduits?
To avoid induced noise on the data and to keep systems of different voltage separated, which is a safety requirement as well as good practice.
What is verified before an installation is considered finished?
Insulation resistance, continuity of the protective conductor at every point, operation of the RCD and grounding resistance, all documented in a test report.