Upgrading a Consumer Unit
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Upgrading a consumer unit from one using rewireable BS 3036 fuse carriers to a 17th edition split load board incorporating miniature circuit breakers MCBs, protected by residual current devices, RCDs is a job that many people in older style properties will have to consider. This is partly to do with safety, becuase of the increased use of electricity it is often a better and cheaper option to upgrade the ‘fuse box’ and partly because alterations to the installation require compliance with the new wiring regualtions
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Consumer unit to be up graded |
Consumer unit with fuse carriers removed |
17th edition wiring regulations relating to consumer units
The new wiring regulations introduced in 2008 demand that all circuits are protected by RCDs. Often the easiest way to comply, particularly if the existing fuse box is dated, is to upgrade.
Swapping the consumer unit may also involve some additional electrical work to enable the installation to meet the standards set by the new wiring regulations. This might include splitting circuits or running in new cable. An older property might have all the lighting and sockets supplied by just two circuits. It would be better practice to split these so that the lighting and sockets for each floor are on separate circuits with there own MCB. Other problems that require attention include borrowed neutrals. This is where a neutral return path was not available and a link to another circuit has been made. Correcting this fault would, in many cases, require a new cable to be laid back to the consumer unit.
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Old consumer unit removed |
Removing obsolete cables |
Checking earthing and bonding arrangements
Before the consumer unit is changed, the electrician will have checked the distributor’s equipment at the origin of the installation and the earthing and bonding arrangements. This is to ensure that they are safe and that they comply with the regulations. Many older properties do not have a double pole isolation switch between the meter and the consumer unit meaning that the electrical distributor will have to be called in before work on the consumer unit can start. The distributor will often oblige by installing this main switch.
Most domestic properties have the following arrangement at the origin: the service cable entering a sealed unit with a fused line (live) conductor with a 100amp main fuse or service cut-out, 25mm meter tails, a digital or analogue meter, 25mm tails to consumer unit. It is here that the main switch would be placed. The ‘automatic disconnection of supply’ would be provided for by 16mm earthing conductor and 10mm main bonding conductors to gas, water and other services. These arrangements vary with larger or smaller installations; your electrician will advise you on what is required.
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Installing wall support |
Making first connections to 17th edition RCD board |
Installing the new consumer unit
The photographs on this page show an old style fuse carrier type consumer unit being changed for a new 17th edition split load double RCD type consumer unit. This type of consumer unit has two RCDs as well as a main isolator.
The nature of this work, disconnecting the overload protection and connecting the cable to a new means of basic and fault protection means that the electrician will have worked on all circuits. He will therefore have to conduct a test on all circuits to ensure that they are safe and will then have to issue an electrical installation certificate before the job is handed over. Any faults found on a circuit will have to be corrected before the circuit is energised.
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Organising circuit connections |
New consumer unit in place ready for labelling |
Safety Note
Before any work is carried out on an electrical circuit, the circuit must be isolated and locked off or the fuse carrier removed. A sign should be placed at the isolation point saying that work is being conducted and that power must not be returned to the circuit.
If you are not 100% sure that you know exactly what you are doing call in a qualified electrician. Building regulations are becoming stricter, requiring that competent persons only carry out electrical work, with most works having to be notified to the local authority. Modifying the electrical installation in your home could be against the new rules and could invalidate your home insurance, if in doubt check first!
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