Martindale classic check plug socket tester case is made from flame retardant ABS.
When plugged into a live 13 A socket it will identify almost all electrical faults which can be instantly identified using the key on the face label.
Three long life high intensity neons indicate when the circuit is correctly wired. This fail safe system means any neon not lit indicates a problem.
This check plug induces less than 5 mA of earth leakage, well below RCD trip thresholds.