Page 14 - Electrical Installation in Hazardous Area

Contents xi

13.2.3 Interconnections 335
13.2.4 Simple apparatus 335
13.2.5 The intrinsically safe circuit 335
13.2.6 The intrinsically safe system 336
13.3 Levels of intrinsic safety 336
13.3.1 Intrinsic safety category ’ia’ 336
13.3.2 Intrinsic safety category ‘ib’ 337
13.4 Countable and non-countable faults 337
13.4.1 Non-countable faults 338
13.4.2 Countable faults 338
13.4.3 Effects of other faults 338
13.4.4 Infallible component, assembly or
interconnection 339
13.5 Confirmation of intrinsic safety in respect of arc and
spark ignition 339
13.5.1 Achievement of safety factors 343
13.5.2 Assessment of circuits 344
13.6 Confirmation of intrinsic safety in respect of hot
surface ignition 353
13.7 Basic component and construction requirements 357
13.7.1 Safety factors on component rating 357
13.7.2 Specific requirements for particular
components 359
13.8 Component and circuit failure modes 370
13.8.1 Wire and printed circuit tracks 371
13.8.2 Connections 371
13.8.3 Capacitors and inductors 371
13.8.4 Resistors 372
13.8.5 Semiconductors 372
13.9 Apparatus construction requirements 374
13.9.1 Enclosures 374
13.9.2 Internal layout (wiring, printed circuit
boards, etc) 375
13.9.3 Earth conductors and connections (including
terminals) 382
13.9.4 Encapsulation 384
13.10 Infallible components, assemblies and construction
elements 385
13.10.1 Infallible transformers 386
13.10.2 Damping windings 394
13.10.3 Current limiting resistors 394
13.10.4 Blocking capacitors 395
13.10.5 Shunt safety assemblies 396
13.10.6 Internal wiring and connections 398
13.10.7 Galvanic separation 400