11.3 Optical Fibre Safety, Electrical Permits & Site Installations

11.3 Optical Fibre Safety, Electrical Permits & Site Installations

The Electrotechnical topic of the ECS assessment reaches beyond safe isolation. The syllabus includes safe working with optical fibres, and the question bank also asks about electrical permits to work, how often construction site installations are inspected, nominal supply voltages, replacing fuses, and the competence the Electricity at Work Regulations require. This section brings those topics together.

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Optical Fibre Safety

Data and telecoms installers handle optical fibre every day, and electricians increasingly terminate and test it. There are two separate hazards.

1. Glass fibre fragments

Stripping, cleaving and terminating fibre produces tiny, sharp glass offcuts that are almost invisible. They can pierce the skin or eyes, are hard to remove once embedded, and can cause infection. Fibre offcuts are not hot, toxic or a source of laser light; the danger is mechanical.

Safe working practice:

• Work on a dark mat or surface so that fragments are easy to see.
• Put every offcut straight into a dedicated, labelled fibre waste container, such as a sealed sharps-type pot. Never leave remnants lying around on site, on benches or on the floor.
• Wear safety glasses while cleaving and terminating.
• Do not eat, drink or smoke in the work area, and wash your hands afterwards so that fragments are not swallowed.
• Never brush fragments away with your hand; pick them up with sticky tape.
• Do not rub your eyes while working with fibre.

2. Light sources

Optical fibre systems and test equipment use lasers or highly concentrated visible or infra-red light. Much of this light is invisible, so a fibre can be carrying light without appearing lit, and exposure can damage the eyes or cause blindness.

• Never look into the end of a fibre or connector, and never point a fibre end towards your own or anyone else's eyes.
• Treat every fibre as live until confirmed otherwise, and use an optical power meter to check rather than looking.
• Fit dust caps to unused connectors.
• Follow the laser safety class marked on equipment (BS EN 60825 series) and the system owner's rules.

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Electrical Permits to Work

An electrical permit to work is primarily a statement that the circuit or equipment has been isolated and is safe to work on. It identifies the circuit or equipment covered, explains how it has been made safe (isolation points, locks and earths), and describes the work to be done. Because it certifies that equipment is dead, a permit to work is not used for live working.

The person receiving the permit signs to accept it, keeps it while the work is in progress, and returns it for cancellation when the work is finished, so that the system cannot be re-energised while anyone is still working on it.

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Construction Site Installations

Temporary electrical installations on construction sites take far more punishment than permanent ones, so they need frequent checks:

• Periodic inspection and testing every 3 months is recommended for construction site installations (IET Guidance Note 3).
• Distribution assemblies must be robust, weatherproof, lockable and protected against damage.
• Socket-outlets for tools are normally 110V yellow (BS EN 60309); 230V blue outlets serving site cabins and some equipment need 30 mA RCD protection.
• Cables should be routed to avoid damage from plant and materials, and protected where they cross routes.

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Nominal Voltages

The nominal single-phase voltage in the UK is 230V, and the nominal three-phase voltage is 400V between lines; these values are harmonised with the rest of Europe. On construction sites, tools run at 110V (55V to earth), and hand lamps in confined or damp places at 50V or less (SELV).

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Fuses

A fuse is often the main safety device in a circuit. A blown fuse must only be replaced with a fuse of the correct type and rating, and only after the cause has been found. Never replace a fuse with a nail, silver foil, a bit of wire or a higher-rated fuse: none of these will disconnect the circuit when a fault occurs, so cables can overheat and catch fire and faulty equipment can stay live.

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Competence and Exposed Cables

Regulation 16 of the Electricity at Work Regulations requires anyone working on electrical systems to have the appropriate technical knowledge or experience, or to be appropriately supervised. Being an electrician is not enough on its own; you must be competent for the particular task.

If your work takes you near hanging cables with bare ends, keep well away and inform your supervisor. Always assume exposed cables are live until you know otherwise; you cannot tell by looking, and touching them to find out can kill.

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ECS Exam Focus

• Optical fibre remnants are dangerous because they can pierce the skin or eyes.
• Never point a fibre end at anyone's eyes: the beam can damage the eyes.
• An electrical permit to work states the circuit or equipment has been isolated and is safe to work on.
• Dead working on high-voltage systems always requires a permit to work.
• Construction site installations: inspected and tested every 3 months.
• UK nominal single-phase voltage: 230V.
• No spare fuse? Use none of the improvised alternatives.