Page 15 - Electrical Installation in Hazardous Area

xii Contents

13.11 Diode safety barriers 402
13.12 Input and output specifications 406
13.13 Examples of fault counting in apparatus 411
13.14 Intrinsically safe systems 415
13.14.1 Interconnecting cable systems 419
13.14.2 Cable parameter measurement 424

14 Apparatus using protection concept ’N (‘n’) 427
14.1 The situation in respect of standardization 427
14.2 Basic requirements of the protection concept 429
14.3 General constructional requirements 430
14.3.1 Environmental protection 430
14.3.2 Mechanical strength 431
14.3.3 Wiring and internal connections 432
14.3.4 External connection facilities 433
14.3.5 Conductor insulation and separation 433
14.4 Additional requirements for certain types of
non-sparking apparatus 437
14.4.1 Rotating electrical machines 437
14.4.2 Fuse links and fuseholders 438
14.4.3 Fixed luminaires 438
14.4.4 Portable luminaires and other light sources 441
14.4.5 Electronic and low power apparatus 442
14.5 Apparatus producing arcs, sparks and/or
ignition-capable hot surfaces 443
14.5.1 Enclosed break devices and non-incendive
components 443
14.5.2 Hermetically sealed devices 445
14.5.3 Sealed devices 447
14.5.4 Energy limited apparatus and circuits 447
14.5.5 Restricted breathing enclosures 450

15 Protection concepts for apparatus for dust risks 456

15.1 Situation in respect of standardization 456
15.2 Basic types of apparatus for use with combustible dusts 458
15.2.1 Degrees of enclosure 458
15.3 Operational requirements 459
15.4 Basic constructional requirements 461
15.4.1 Enclosure materials and mechanical strength 461
15.4.2 Joints intended to be opened in normal service 462
15.4.3 Semi-permanent joints 464
15.4.4 Spindles and shafts 465
15.4.5 Light-transmitting parts 465
15.4.6 Fasteners 466