Upgrading a Consumer Unit

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Upgrading an old consumer unit to one incorporating two residual current devices, RCDs is a job that many people will now have to consider. The 17th edition of the wiring regulations requires most circuits in a domestic property to be protected by an RCD. It is often a better and cheaper option to upgrade the consumer unit rather than alter the existing installation in order to comply with the new regulations.

This was the case in the installation shown in the photographs on this page. A consumer unit using rewireable BS 3036 fuse carriers was upgraded to a 17th edition split load board incorporating circuit breakers sometimes referred to as MCBs, miniture circuit breakers. The circuits on the new consumer units are protected by two residual current devices. Power and lighting circuits for the same floor are split between the RCDs on different sides of the board. This is so that in the event of a fault all the circuits on a particular floor are not cut-off from the supply.

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Consumer unit to be up graded Consumer unit with fuse carriers removed

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 their own circuit breaker. 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.

Consumer unit with fuse carriers removed Removing obsolete cables

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 may 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.

Installing wall support Making first connections to 17th edition RCD board

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 an electrical 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.

Organising circuit connections New consumer unit in place ready for labelling

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 carried out 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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