A properly protected electrical installation is the foundation of safety in every home. Even the best equipment will not help if the protection devices are incorrectly selected or grounding is missing. Below we discuss the key elements of electrical protection.
Residual Current Devices (RCD)
An RCD detects the difference in current between the live and neutral conductors. When this difference exceeds the rated value (typically 30 mA for personal protection), the device disconnects the supply in under 40 ms.
- Type AC — responds to sinusoidal alternating current,
- Type A — also responds to pulsating DC (required for PV inverters, EV chargers),
- Type B — detects smooth direct current as well; used in special industrial applications.
A domestic consumer unit should have at least two 30 mA RCDs — one for lighting circuits and one for socket outlets.
Surge Protection Devices (SPD)
Atmospheric and switching surges can reach several kilovolts. Class T1+T2 (formerly B+C) surge arresters are installed at the main distribution board input. For sensitive circuits (IT equipment, home automation) an additional T2+T3 stage is recommended.
- The SPD must be connected to a functional earth with resistance ≤ 10 Ω,
- An upstream backup fuse is required — typically gG 125 A for T1+T2.
Earthing and Bonding
The TN-S earthing system is the standard in new construction. The protective conductor PE must be routed separately from the neutral N from the distribution board onward. Main equipotential bonding connects the PE busbar to:
- metallic water pipes,
- gas pipes,
- foundation reinforcement (foundation earth electrode),
- structural metallic elements of the building.
Earth resistance should be below 10 Ω, and measurements are carried out every 5 years.
Miniature Circuit Breakers (MCB)
MCBs protect cables against overload and short circuit. Selection depends on the cable cross-section:
- 1.5 mm² cable → MCB B10 or B16 (lighting circuits),
- 2.5 mm² cable → MCB B16 or B20 (socket circuits),
- 4.0 mm² cable → MCB B25 (cooker, water heater).
B-curve MCBs trip at 3–5× rated current, which is suitable for residential installations. C-curve (5–10×) is used for loads with high inrush current.
Protection Classes and IP Ratings
Equipment inside the distribution board should have at least IP30 protection (indoors) or IP65 (outdoors). Bathroom sockets in zone 2 require at least IP44 and must be supplied through a 30 mA RCD. Correct IP rating selection prevents moisture and dust ingress, which is crucial for equipment longevity.