Lighting Circuits Without an Earth
Work in progress.
Many lighting circuits (usually from pre 1966) are still in use that have no earth or conductive protective core (cpc). Whilst the rewiring of these circuits is the preferable solution, for many people the cost of installation and redecorating can be prohibitive.
If a rewire is not an option then the following steps should be taken for safety reasons
1. Class I (metal) light fittings and accessories should be replaced with Class II (plastic/insulated) fittings
2. Resistance test. The circuit should be tested between the line conductor (line and neutral connected together) and the earth terminal of the consumer unit. The resistance should be at least 1 Megohm. If the resistance is less that 1 Megohm the circuit must have additional RCD protection. The test should also be repeated between the line conductor and any exposed conductive part of the circuit (eg the screws for a lightswitch with a metal backbox). Again f the readings are less than 1 Megohm RCD protection will be required.
3. RCD protection. It is advisable to have 30mA RCD protection on lighting circuits that have no cpc and essential if the resistance readings are lower than 1 Megohm.
5. 2 and 3 pin sockets. Any 2 or 3 pin sockets connected to the lighting circuit that may be used for portable equipment should be disconnected.
Not having a cpc on a lighting circuit makes it impossible to safely extend the circuit should you require extra lighting points and many electricians may refuse to swap a fusebox for a CU unless the old lighting circuit is also rewired.