RCD types explained: AC, A, F and B — which one for an EV charger?

Written by Engin Demirel · Electrical technician, master instructor · 12 years of experience

Short answer: An RCD's type shows which forms of leakage current it can detect. Type AC detects only sinusoidal leakage; type A also detects pulsating DC from electronic devices; type F adds mixed-frequency leakage from single-phase inverter appliances; type B detects all of these plus smooth DC. Use type A in homes, type F on circuits with inverter washing machines and heat pumps, and type B for EV charging (or a charger with 6 mA DC leakage detection plus a type A RCD). Local rules apply.

Types and what they detect

Type AC: alternating (sinusoidal) leakage only. Often inadequate in today's electronics-heavy homes.
Type A: AC + pulsating DC leakage (switch-mode power supplies, LED drivers, dimmers). Recommended for homes.
Type F: type A + mixed-frequency leakage (inverter washing machines, air conditioners, heat pumps, single-phase frequency converters). More resistant to nuisance tripping.
Type B: type F + smooth DC leakage. Required for EV chargers, three-phase inverters, solar systems and some medical equipment.

Smooth DC leakage can "blind" a type A RCD so that it fails to trip in a fault, which is why type B matters.

Sensitivity: 30 mA and 300 mA

30 mA: protection of people; used in homes and on bathroom, socket and outdoor circuits.
300 mA: fire protection; used at the main incomer or in large installations, time-delayed (type S) for selectivity.
10 mA: some special wet-area and medical applications.

Which RCD for EV charging?

The charger and the car can produce smooth DC leakage in a fault. The charging circuit therefore needs either:

a type B 30 mA RCD, or
a charger with built-in 6 mA DC leakage detection (RDC-DD) plus a type A 30 mA RCD.

Many home chargers include 6 mA DC detection; it is listed in the product's technical data. The charging circuit is also run as a dedicated circuit with its own breaker.

Why does an RCD trip?

Genuine leakage: a damp junction box or socket, damaged cable, faulty appliance with a heating element (water heater, washing machine, oven).
Cumulative leakage: small leakages from many electronic devices on one RCD can add up past 30 mA. Splitting circuits across several RCDs solves this.
Surges: lightning or grid surges; surge protection and surge-resistant RCDs help.

If an RCD keeps tripping, unplug appliances one by one to find the faulty one; never bypass the RCD.

The test button

The "T" button checks that the mechanism works; pressing it monthly or quarterly is recommended. Trip time and current are measured by a qualified person with an RCD tester.

In Bursa, ENGN provides consumer unit upgrades, RCD protection and EV charger installation.

Frequently asked questions

What is the difference between type A and type AC RCDs?

Type AC detects only sinusoidal leakage; type A also detects pulsating DC leakage from electronic devices. Type A is recommended for homes.

Where is a type B RCD used?

Wherever smooth DC leakage can occur: EV chargers, three-phase inverters, solar systems and some medical equipment.

Which RCD does an EV charger need?

A type B 30 mA RCD, or a type A 30 mA RCD combined with a charger that has 6 mA DC leakage detection.

What is a type F RCD for?

It detects mixed-frequency leakage from single-phase inverter appliances (washing machines, air conditioners, heat pumps) and is more resistant to nuisance tripping.

30 mA or 300 mA?

30 mA protects people; 300 mA is for fire protection. Home circuits need 30 mA.

Why does my RCD keep tripping?

A damp junction box or socket, damaged cable, faulty heating appliance, or the combined leakage of many devices on one RCD. Unplug appliances one by one to find the fault.