International Gas Detectors TOC-635, Installer'S Manual

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IGD Installations are undertaken to the requirements of BS7671:2018 and subsequent ammendements, in
particular Annexe A444. Note that this is not concerned with placement of gas detectors but relates to the
installation cabling requirements.
In Addition to BS7671 there are other relevant standards relating to cable segregation to minimise electrical
interference. In the UK are B6701:2016, which is safety standard, and BS EN 50174-2 Information technology
- Cabling installation - Part 2: Installation planning and practices inside buildings. BS EN 50174-2 is more
concerned about the electromagnetic compatibility issues (interference) between power and data cables,
rather than safety, but does state that safety issues take precedence over EMC issues. Within the Process
sector, the current guidance is BS6739:2009 - Code of practice for instrumentation in process control systems:
installation design and practice. For this standard IGD addressable systems are considered as Classification
4. Communications signals. This group includes fieldbuses, ethernet and other digital communication systems
such as CAN-based systems, and analogue/digital hybrids.
For our purposes a power cable is defined as above 50 V AC with a 10 A rating
In General
• Parallel runs of instrument cables and power cables should be avoided; however, where unavoidable,
adequate physical separation should be provided. A spacing of 200 mm is recommended from a.c. power
cables up to 10 A rating. For higher ratings the spacing should be progressively increased.
• Where a cross-over between signal and power cables is unavoidable, the cables should be arranged to cross
at right angles with separation of at least 200 mm maintained by positive means
• Power and gas detection cables are installed with a 200 mm separation wherever possible
• A 600 mm separation should be maintained between gas detection cabling and three phase power cables
• Where 200 mm separation isn’t possible then the reduced distances of Table 3 may be used
• A 50 mm separation must be included as defined in BS 6701
• A suitably earthed armoured power cable may be considered as ‘screened’ for the purposes of cable
segregation
• Failure to observe the above rules may lead to non compliance with The Electricity at Work Regulations 1989
and the EMC Regulations 2006 (SI 2006/3418) July 2007
• Failure to observe the above rules may lead IGD to withdraw any terms of Warranty associated with their
Gas Detection products for the specific installation concerned
The Following Examples Show Typical Cabling Schemes
CABLE INSTALLATION STANDARDS