Seaward A252 - Manual (Page 3)

A252 Portable Appliance Tester INTRODUCTION
M ETHODS OF C ONSTRUCTION FOR E LECTRICAL S AFETY
To provide the user with protection against electric shock general methods of construction must ensure
firstly that all 'live' parts are insulated and secondly that should this basic insulation fail the 'live' parts are
prevented from creating a hazard to the user.
This second level of protection is achieved either by 'earthing' all accessible conductive surfaces or by
providing 'double insulation' in the form of a second insulating layer or by reinforcing the primary insulation
layer.
Earthed equipment is referred to as Class I and earthing is achieved by connecting all accessible
conductive surfaces (the tool body or outer casing and associated fixings etc.) to the supply earth via a low
impedance protective conductor, then if any 'live' part comes into contact with these surfaces the hazardous
current is drawn harmlessly to earth through the protective conductor rather than through the person
holding the tool. The protective conductor is the green/yellow 'earth' wire in standard 3 core mains supply
leads.
Double insulated equipment is referred to as Class II. All accessible conductive surfaces are additionally
insulated from internal 'live' parts and components. No 'earth' wire is present in the supply lead. All Class II
equipment is identified by a prominent square within a square symbol.
D0010024.DOC (01/01/94) Page 3 INSTRUCTION MANUAL