old fuse box to a new consumer unit
Firstly, replacing a consumer unit in domestic premises in England and Wales is notifiable work under Part P of the Building Regulations. Unless the work is undertaken by a person registered with an electrical self-certification scheme such as the NICEIC, notification of the proposals to carry out the work must be given to the appropriate building control body before the work begins. Plugs Electrical are an NICEIC Approved contractor so the new consumer unit will be notified to local building control as part of the work and a Part P Building Regulations certificate of compliance issued at the end of the job.
The next step is to carry out an Electrical Installation Condition Report. The purpose of this is to ascertain the condition of the existing wiring, identify potential hazards such as faulty connections or outdated components and determine if the system can support the new consumer unit. The existing meter tails, earthing and bonding will also be checked to confirm adequate current-carrying capacity and sizing respectively. Any issues found at this stage will need to be rectified prior to the installation of a new consumer unit. The only time a condition report is carried out after a consumer unit replacement is when what is called a ‘distress change’ is needed. This is when an existing consumer unit/fuse board has suffered mechanical damage, is unusable after damage from overheating or is in a dangerous condition with exposed live parts.
Finally, once it is established that all is well with the existing installation the new consumer unit can be installed. The new unit will have Miniature Circuit Breakers (MCBs) and Residual Current Devices (RCDs) incorporated for maximum electrical safety. New units will also have Surge Protection Devices (SPDs) for the protection of sensitive electronic equipment. Please be aware it will be necessary to turn the power off to the property for a few hours whilst the consumer unit change takes place. A temporary supply can be requested and provided to keep such things as internet connections on.
There are 4 main consumer unit configurations to choose from:
1: All independent circuits - With an ‘all independent’ consumer unit each circuit is fed from its own circuit breaker with a built-in residual current device (RCBO). This means that if a fault causes the RCBO to trip, it will only disconnect the circuit with the problem and all the others will carry on as usual. This configuration is considered best practice and is the one Plugs Electrical recommend and install the most.
2: No independent circuits - A ‘no independent circuits’ consumer unit is the consumer unit configuration that has generally in the past been used the most. It splits the consumer unit into two halves. Each half having an RCD protecting multiple circuits. This means that a circuit that trips one of the RCD’s would also mean the disconnection of all the circuits connected to that same RCD. The other side of the consumer unit connected to the other RCD would stay energised. Although popular in the past this configuration is seen as outdated these days due to the cheaper cost of RCBOs and the wiring regulations encouraging installers to use the ‘all independent’ configuration to comply fully.
3: Half Independent circuits - With a ‘half independent’ consumer unit, half the circuits are fed from their own independent RCBO’s and the second half are fed from independent MCB’s but which are protected by a single RCD. If one of the independent circuits on the first half of the consumer unit develops a fault and trips that circuits RCBO then only that circuit will be disconnected from the supply and the other independent circuits will be fine as well as the circuits on the second half of the consumer unit that are on the single RCD. However If any of the circuits on the second half of the consumer unit develop a fault that trips the RCD protecting them then they will all be disconnected from the supply but the independent circuits on the first half of the consumer unit will not.
4: Some independent circuits - With a ‘some independent circuits’ consumer unit, the consumer unit is split in half with one half protected by one RCD and the other protected by another RCD. There is also room for some independent circuits which are not protected by either of these RCD’s but are on their own individual RCBO’s. If either of the two RCD’s trip they will disconnect all the circuits connected to that RCD but not the other one or the independent circuits. If one of the independent circuits trip they will only disconnect that circuit and no others.
Please contact Tony at Plugs Electrical if you require a consumer unit upgrade or if you just have more questions about the replacement of an old fuse board with a new modern consumer unit.
