The laserliner socket tester plus is a professional wiring and rcd tester for conducting a quick electrical wiring check for user safety and prevent damage to expensive electrical equipment verification checks include polarity earth voltage and an rcd test the rcd test verifies that an rcd rated at 30m a will trip within 300ms when a nominal 30m a earth fault current is applied faults are indicated through 3 indicator lights showing missing neutral connection missing earth connection live faults