Choosing the RCD type

Type AC only detects pure sinusoidal AC fault current. It is not permitted in dwellings and is explicitly prohibited for charging points. Do not use it in new installations — always start at type A as a minimum.

Type A detects sinusoidal AND pulsating DC fault current and is the standard choice in homes and commercial premises. New dwellings must have at least 2 RCDs of type A with max. 30 mA rated residual operating current.

Type F covers type A's fault types plus certain mixed frequencies from single-phase frequency converters (e.g. modern washing machines and heat pumps). Choose it where the equipment manufacturer recommends at least type F.

For a charging point, the choice depends on whether the charging unit has an approved, integrated DC fault-current detection (RDC-DD ≤ 6 mA DC per IEC 62955). Always obtain manufacturer documentation confirming this.

If the charging unit has approved DC blocking, type A (or type F/A-EV) is sufficient. If it does NOT have approved DC blocking, type B is required — it also detects smooth DC fault current up to 1000 Hz. Type A alone is then insufficient, whatever industry practice says.

Type B is more expensive (guideline ~1,500–3,000 kr. each, vat.dk), but is a legal requirement without approved DC detection.

For personal protection, I_ΔN is max. 30 mA. To avoid nuisance tripping, the total operating leakage current per RCD group must not exceed 0.3 × I_ΔN — i.e. max. 9 mA on a 30 mA group. Spread the loads over several RCDs if the leakage current becomes too high.

In a TT system, the fault current is limited by the resistance of the earth electrode, and the rated residual operating current must satisfy I_ΔN ≤ 50 V / R_A, where R_A is the sum of the resistances of the earth electrode and the PE conductor. Use the RCD calculator for the specific limit.