Old electrical installations

There are millions of old electrical installations still in daily use, right across the country. While many of these should be safe and functional, they may not offer all of the facilities and protection mechanisms that a modern install will offer.

This article attempts to collect together notes on the likely pitfalls of older installations, and give tips for how to live with and improve them.

How old?

How do you tell the age of an installation? The Dating Old Electrics page should give you some clues.

General notes on old circuits

Common problems include:

• Lack of RCD protection, greatly elevating the risk of injury from electric shocks.
• Substandard or missing Euipotential Bonding
• Undersized protective conductors in circuits that can result in slow clearing of faults (or even failure to clear in some cases). (on very old installations, proper earthing may not be complete or present at all)
• Badly perished rubber insulation creating a high risk of insulation failure.
• Light switches that can sit in mid position, and if luck deserts you, sit in an almost on position and arc. This either burns the switch out or causes a fire.
• Dirt buildup at connection points. This can cause [[Electrical_Circuit_Faults|circuit faults], insulation breakdown, and fire & shock risk.
• Poor connections. Connections can deteriorate due to decades of thermal cycling, wire corrosion, or less than ideal design & construction of historic fittings.
• Flammable wiring enclosures, such as wooden pattresses behind light switches and sockets.
• Light switch covers that undo easily by hand, a danger primarily to children.

Missing features and their effects

Item	Significance
RCD Protection	A functional and regularly tested RCD will massively reduce the likelihood of being injured by an electrical shock. Modern installations will usually protect all circuits with several RCDs.
Equipotential Bonding	Equipotential bonding is used to limit the voltage that one is able to indirectly come into contact with during fault conditions. It is of particular importance in areas where people are particularly vulnerable to electrical shock injury, such as bath and shower rooms. Bonding also helps mitigate the risks of conductive parts of a house's structure (such as its pipework) from projecting the effects of a fault from one room into another. Lastly, bonding will help minimise the risk that a fault in the earth connection itself supplied to the property does not manifest as a dangerous situation in the property itself.
Adequate circuit separation and discrimination	Lack of adequately separated circuits, may mean that faults cause more inconvenience and consequential risks (e.g. trips and falls in the dark) than they would with a modern installation. For example and old installation may only have one lighting circuit, and hence a blown fuse will mean no lights anywhere.
Adequate power and lighting points	Older installs rarely have enough power sockets for modern patterns of use. They also encourage multiple extensions of existing circuits (with varying degrees of workmanship and design care).
Modern MCBs	Modern MCBs offer simpler detection and resetting of tripped circuits. They are also not open to abuse in the way that re-wireable fuses are (you can't "repair" a circuit that is repeatedly tripping due to a fault with tinfoil!) Notw however that MCBs can also introduce new problems, since they are more sensitive to short term overloads, which can result on nuisance trips when tungsten filament lamps fail.
Expansion Capacity	Often old fuse boxes will have no spare ways. This makes adding new circuit in a sensible and well partitioned way more difficult and expensive.

See Also

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• Wiki Subject Categories