Basic AREI terms
Below are some of the core AREI concepts you will keep running into when you design residential installations. They are intentionally written in plain lang
Below are some of the core AREI concepts you will keep running into when you design residential installations. They are intentionally written in plain language, but they still use the proper technical words so you can recognise them in reports and inspection notes.
Circuit
A circuit is a set of conductors, protection and loads that are protected together by the same overcurrent device (MCB, RCBO, fuse).
On the drawings you can think of it as “one line on the one‑line diagram”: one breaker, one set of cables, and the sockets / lights / fixed appliances behind it.
AREI rules care about:
- what type of circuit it is (lighting, socket, mixed, fixed appliance, cooker, EV, …),
- how many users sit on it,
- which protection and cable size you choose.
Residual Current Device (RCD / differentieel / disjoncteur différentiel)
An RCD measures the difference between the current going out and the current coming back. If some of that current is leaking to earth – for example through a person – the RCD trips.
In residential AREI practice:
- a 300 mA device at the origin mainly protects against fire,
- 30 mA devices downstream protect people on sockets, mixed circuits, bathrooms, outdoor circuits, EV, etc.
In Condui you see them as separate protection devices or combined as RCBOs.
Breaker / overcurrent protection
A breaker (MCB, disjoncteur) or fuse protects cables and equipment against overload and short‑circuit. It has:
- a rated current \(In\) – the current it will allow continuously, and
- a tripping curve (B / C / D) which describes how fast it reacts.
AREI 5.2.2 says that In must not exceed the admissible current of the cable. That is why you regularly see checks like:
- “breaker vs cable cross‑section”, and
- “cascading breaker ratings” between upstream and downstream devices.
Cable cross‑section (mm²)
The cross‑section of a cable is the size of its copper conductor in mm² (1.5, 2.5, 4, 6, …).
Larger section:
- can carry more current,
- has less voltage drop,
- but is bulkier and more expensive.
AREI Book 1 §5.2.1 sets minimum sections for types of circuit, for example:
- lighting circuits: typically ≥ 1.5 mm²,
- socket circuits: typically ≥ 2.5 mm²,
- heavier loads and feeders: 4–6 mm² or more.
Voltage drop
The longer and thinner a cable, the more voltage you lose between the board and the load. The RGIE limits this:
- around 3% for lighting,
- around 5% for most other circuits in houses.
For short indoor runs this is rarely an issue. For long garden runs or outbuildings it matters a lot. In practice, you solve problems by:
- increasing the cable section, and/or
- reducing the breaker rating or the design load.
Earthing and equipotential bonding
Earthing provides a low‑resistance path to the earth so that fault currents trip protections quickly instead of energising exposed metal parts.
Equipotential bonding connects metal parts together (water pipes, gas pipes, structural steel, bathroom fittings) so they sit at nearly the same electrical potential.
AREI Book 1 §5.6 goes into detail; on the drawings you normally only see:
- the main earth connection,
- earthing and bonding symbols,
- and sometimes a note about the measured earth resistance.
Bathroom zones
Bathrooms are split into zones (0, 1, 2, outside) with stricter rules the closer you get to the bath or shower:
- Zone 0 – inside the bath / shower: only SELV up to 12 V is allowed, very limited equipment.
- Zone 1 – directly above the bath / shower: only specific IP‑rated and suitably protected equipment.
- Zone 2 – splash zone around: sockets and most equipment must be behind 30 mA RCDs and have the right IP rating.
Even if you do not draw the exact zone boundaries on small residential plans, it is important to understand that circuits feeding equipment in these areas almost always end up under 30 mA protection.