The RCD switch in my small consumer unit in my shed is a 25A 30mA RCD. The switch is knackered but I've found an old one I've had from an older board. It's a 40A 30mA though, is it still ok to use this? Although the supply is only 4mm it is protected by a 32A MCB in the domestic mains board. The CU in the shed only has two circuits, a 20A for two sockets & 6A for a few lights.