Portable Appliance Testing (PAT) testing is concerned with the maintenance of electrical equipment. It is a means of checking the appliance to see if it is safe. The Electricity at Work Regulations require, in Regulation 4(2) that:
As may be necessary to prevent danger, all systems shall be maintained so as to prevent, so far as is reasonably practicable, such danger.

Regular inspection of equipment is an essential part of any preventive maintenance programme.

The scope of the legislation covers everything from small portable equipment e.g. hand drills to fixed 400 kV distribution systems. The requirements apply to fixed and “hard-wired” electrical appliances (or equipment), such as hand driers in washrooms or ovens in commercial kitchens, in addition to portable and hand-held appliances which plug-in, such as drills or vacuum cleaners, both single and three phase. Different inspection and maintenance regimes are recommended for fixed electrical installations and portable electrical equipment.