Consumer Units

Replacing a Consumer Unit (aka fusebox) is a very common request.

There are several reasons to upgrade your consumer unit:

  • Your old one might be damaged.
  • The Prospective Fault Current may be too high for the unit (explanation coming)
  • There may not be enough space to add new circuits.
  • You may wish to upgrade to a safer system. 

Older units had fuses with fuse wire, (often the wrong size!) which rely on a fault generating enough heat to melt a piece of wire to protect you! Then, once you've cleared the fault you have to rewire the fuse, off course it's dark and the batteries in the torch are flat! These units are still OK to use as long as they are in good condition but have limitations if you need to upgrade parts of your installation. Wiring regulations aren't retrospective but old equipment may not be adequate or safe if new wiring or equipment is being installed.

Modern Consumer Units use safety cutouts called RCDs and MCBs instead of rewirable fuses.


From January 2019 all new consumer units have to comply with BS7671:2018.

These require Consumer Units to be constructed of fire resistant materials (ie metal).

This regulation was added because of reports of fires in Consumer Units that are often sited adjacent to escape routes (stairwells, main entrances etc.). Also, in my view, the metal units are much more solid and a better job!

More on RCDs and MCBs


What type of Consumer Unit?

There are two main types of Consumer Unit:

  • 'Split Board' uses 2 (or more) banks of MCBs each protected by a single RCD. The circuits are split between the RCDs so that if an RCD Trips there is lighting or power available on each floor of the property.
    Advantage, Cheaper
    Disadvantage, if an RCD Trips or is faulty all the circuits it protects are inoperable.
  • All RCBOs, an MCB and RCD in one unit, each circuit has its own dedicated RCBO
    Advantage, minimum disruption of RCBO trips or is faulty.
    Disadvantage, more expensive (although coming down in price)

The above types can be combined so that important circuits have a dedicated RCBO.


There are also a number of specialist Consumer Units for special situations ie 'Skeleton Boards' to fit into 'Mantel' enclosures as used in Local Authority housing in the 50s and 60s. Compact boards where space is tight and so on.

Fitting the Consumer Unit:
The Consumer Unit controls and protects every electrical circuit in your home or premises. I will make some preliminary tests before providing an estimate for fitting a new consumer unit to get an idea of the condition of the installation. I will, as a minimum, measure things like the condition of the main earth and check there aren't any obvious dangerous faults.

Ideally, the best course of action is to comission a full 'Electrical Installation Condition Report' to avoid, as much as possible, any unforeseen works (and therefore costs!). However, this is at your discretion.

Isolating the Supply
When replacing a Consumer Unit the power supply has to be isolated to allow safe connection of the new unit.

No electrician should ever be working on a live installation!

As there is a disruption in the power supply you will have make arrangements for appliances like freezers and tropical fish tanks. Modern freezers are usually OK for a few hours but dropping in some freezer packs to be safe might be a good idea.


Scope of work

When fitting a new Consumer Unit the entire installation has to be inspected and tested. A Electrical Installation Certificate (EIC) is issued containing notes from the inspection and all the test results. Any dangerous faults will have to be rectified before the system can be reconnected.

All being well on completion of the works I will issue you with an EIC and submit a notification to the Local Authority Building Control (LABC) through my Competent Person Scheme, ELECSA as required under Part P of the Building Regulations. You will get e receipt for the notification from me and your Local Authority will issue you with an acknowledgement in about 6 weeks.

If the installation is all good then it will not have to be inspected for 10 years (ir in next change of owmership.(5 if a rented property)



As you can see from the above description that there is no such thing as a standard Consumer Unit change as some companies advertise. I always check the installation before giving an estimate and discuss your requirements for now and the future. (you wont want to be replacing the consumer unit again when you build that extension in 3 years time!)


Give me a call if you would like to discuss a Consumer Unit upgrade or request an estimate.


More information:

Electrical Safety Council:

Consumer Unit Replacement in Domestic Premises