In a message dated 16/04/2003 21:23:18 GMT Daylight Time, dcerece...@pelco.com writes:
David The wiring regulations in Europe are based on a CENELEC Harmonised Document (HD) rather than a European Norm (EN) and, as such, it is permissible for requirements to vary from country-to-country in Europe to a much greater extent than is the case for EN 60950, EN 60065, etc. You may therefore find that there is no single answer for the whole of Europe. You say 'high voltage' - but that means different things to a logic designer vs. a power utility engineer. Certainly, in the UK it is not uncommon to run backbone optical fibres in a spiral fashion around the earth return conductor strung between extra-high tension pylons. However, that is a very special application. For mains and optical cables run in a single conduit it is necessary to understand who could access (and damage accidentally) the electrical and optical cables. For instance, it is far from uncommon for underground cables to be damaged by diggers repairing roads etc. Normally, the repairing of optical cables and electrical cables falls to two or more organisations who have operatives specialised in optical safety and electrical safety respectively. Even if only one company is involved in maintaining/repairing both optical and electrical cables, the personnel may well be different. Your application may just be between two linked buildings or even within a single room, but you should nevertheless consider this question. So, are the high voltage cables double-insulated such that they could be touched by untrained personnel? If not, then re-splicing an optical fibre could expose 'optical technicians' to unexpected and unacceptable electrical safety hazards. What is the optical power being transmitted down the fibre? What is the Hazard Level per IEC 60825-2 and would it be acceptable for the 'electrical technicians' to be exposed to this radiation from broken fibres? Within IEC TC76 (responsible for the optical safety standards - IEC 60825 series) and IEC TC 86C (responsible for fibre-optic cable standards) and the ITU-T there has been discussion regarding potential fire hazards caused by the transmission of high optical powers (e.g. in the order of 1W) under certain circumstances. It is a theoretical possibility that a fault in a fibre carrying high optical powers could burn the insulation off of electrical cables carrying high electrical powers, thereby causing an electrical short-circuit. Whether this is the case for you at the moment is something for you to determine - as is the possibility that it is relatively easy to increase the transmitted optical power at some future date. You also talk of optical fibres being insulating. That may be so for certain fibres, but it is also possible to get steel reinforced optical cables. If such optical cables are being used, is the insulation from the high voltage conductors to the (hopefully, earthed) steel reinforcing cables adequate? Of course, your application could just involve running double-insulated mains cables and non-metallic fibres at both Class 1 (825-1) and Hazard Level 1 (825-2) in a single channel for a short run. In such a case you may possible conclude that the potential safety hazards have been reduced to a sufficiently low level. Regards, Richard Hughes Safety Answers Ltd.
