Flash Testing or “High potential dielectric strength testing” is a high voltage Insulation test typically 1500 Volts AC for a Class I or 3000 Volts AC for a Class II and was common in PAT testing up until the IEE Code of Practice 2nd edition was published in 2001. On page 27, paragraph 10.4 it said “Dielectric strength testing is not normally carried out during in-service testing. This is normally carried out by the manufacturer on a complete appliance after assembly”. Page 48 paragraph 10.5 of the new Code of Practice 3rd edition also re-states this; thus flash testing is not normally done now.