The difference in one sentence
Type AC RCDs only detect AC fault current. Type A RCDs detect AC AND DC components — which is what modern appliances actually leak.
Why this changed
Switched-mode power supplies (in LED drivers, EV chargers, induction hobs, computer PSUs, home batteries) generate DC components when they fault. A Type AC RCD can be "blinded" by DC current and fail to trip.
The result: an installation that looks fine on paper but cannot actually protect a person in a real-world fault.
When does Type AC become a C2 on your EICR?
When the load on the circuit is clearly capable of producing DC fault current — induction kitchen, EV charger, dedicated server room. C3 (improvement recommended) is the default for most domestic AC-only circuits today, moving toward C2 as Amendment 4 ages in.
What a compliant upgrade looks like
A modern 6–12 way consumer unit with Type A RCBOs per circuit, SPD (surge protection device) on the incoming, AFDD where applicable, and a 2-hour fault diagnostic before close-out. Our standard package is £750 all-in.
Author byline
James Whitfield, Director & Qualifying Supervisor
NICEIC Approved Qualifying Supervisor, JIB Gold Card Electrician, 10+ years industry experience. Personally reviews every certificate and article published under Electrician London.
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