Quick answer
Type AC only detects sinusoidal AC faults. Type A also detects pulsating DC faults — required for modern appliances like washing machines, EV chargers, and solar inverters.
Most older homes have Type AC RCDs — these only detect certain types of electrical faults. Modern appliances like washing machines, tumble dryers, and EV chargers produce a different type of fault current (DC pulsating) that a Type AC RCD may not detect reliably. Type A RCDs detect both types. When your electrician replaces your consumer unit or adds new circuits for modern appliances, they should install Type A protection. If you are having an EV charger installed, a Type A or Type B RCD is a requirement.
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