Domestic Electrical Installations 
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  • Glossary

    CFL – Compact Fluorescent Lamp. The current mainstay low energy lamp, available in a wide range of cap fittings. Most take a short while to warm-up to their maximum brightness, although some types appear very much worse than others.  Although more expensive than the traditional tungsten filament GLS bulbs, they have a much greater life time, and use significantly less energy, giving significantly lower lifetime costs. See for more.

    GLS – General Lighting Service. A generic name for the standard tungsten filament bulb.

    LED – Light Emitting Diode.  A low energy light source. Low light output types have been around for many years and are often used for small accent lighting sources, but more recently much higher output versions have become available. These are still very expensive, but should get cheaper soon. The lamps typically have very long lifetimes (but can be damaged by excessive heat build up), and do not suffer from the long warm-up time associated with CFL’s. See for more.

    MCB – Miniature Circuit breaker. The modern version of a fuse. These protect an electrical installation from fire in the event of an overload or short circuit by rapidly disconnecting the supply. Unlike old fashioned rewireable or cartridge fuses they can be reset by simply operating the MCB switch once the fault has been removed.

    PIR – Passive Infra Red (detector). A device that detects the movement of people (and larger animals) by sensing body heat. Used to automatically switch on/off lights, or operate burglar alarms.

    RCBO – Residual current operated circuit breaker with overcurrent protection. In other words an RCD and MCB combined in a single device. These can be used in a fuse box instead of MCBs to provide separate RCD protection to each individual circuit, thus minimising the inconvenience when a fault causes a trip. However, this comes at a cost…

    RCD  -  Residual Current Device. A safety device that quickly disconnects the supply when even a small fault current flows from the live conductor to earth. See The Electrical Safety Council web site advice for RCDs at The current wiring regulations require that all socket outlets, and in most cases all other circuits are protected by these. The circuits should be split across at least 2 separate RCD zones, so that the whole house in not plunged into darkness when a trip occurs. An RCD has a test button that should operate the cut-out when pressed. (Note that some older installations may have a similar looking “Voltage operated earth trip switch”. These can be identified by the presents of two earth wires – green or green/yellow sheaths – being connected to the device. They are usually separate from the fuse box. These devices are no longer considered effective and should be replaced).

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    Ring & Radial, 47 Park Lane, West Grinstead, Horsham, West Sussex, RH13 8LT