What is a consumer unit?
The consumer unit provides protection against electric shock and it’s also responsible for powering all the electrical circuits in the home. It is vital you know where your consumer unit (fuse box) is in your home in case of an emergency.
What is inside a consumer unit?
All of the components within the consumer unit play a fundamental role in guaranteeing safety and integrity for each installation.
Enclosure – This is the ‘box’ all of the relevant accessories are housed in. Since the introduction of the 18th edition, all new installations must be in a steel enclosure
Earth Bar – This is the common connection point for all circuits’ earth cables. All circuit protective conductors will connect on the earth bar along with earth bonding connections
Neutral Bars – The common connection point for the neutral cables from the earth leakage protection devices (RCBOs)
Din Rail – This is the metal bar that all circuit protection devices mount to, they usually clip on very easily. This sits on the inside back of the consumer unit, facing outwards. It does not carry any electrical current
Busbar – You probably won’t ever see the busbar, it is a long strip of copper, which has big ‘teeth’ on it to lock the circuit breakers and main switch securely
Main Switch – The main switch controls the electrical supply in your home, and allows you to isolate all circuits by simply turning it on and off. Everything within your consumer unit is controlled by the main switch
MCB – Also known as Mini Circuit Breakers, this protects appliances from overload. They come in a range of amperages from 6a to 50a in domestic installations. Nowadays a 32amp is used to protect an SPD which is installed in the fusebox
RCD (Residual Current Device) – An RCD protects humans against electric shock by measuring the total outgoing current against the total incoming current. If the two change and become different this means there is a problem and electricity has gone missing – this is known as ‘earth leakage’. The RCD will then cut the power to all circuits protected by the RCD. These devices are becoming less common due to RCBO main switchboards being preferred because of regulations and safety
RCBO (Residual Current Breaking with Overload) – An RCBO is an intelligent bit of kit which combines the functions of both an MCB and RCD, protecting against both overload and earth leakage. They are now the most popular choice for electricians due to the added safety, although they initially cost more their functionality and safety features outweigh going to the RCD/MCB route
Blanks – Blanks are pieces of plastic which clip to the din rail in just the same way as any circuit protection device and allow for future changes and additions to the circuit design. If you wanted to add a circuit for outdoor lighting for example – the consumer unit and busbar are ready to accept the MCB which would protect this circuit without any reconfiguration of the consumer unit
SPD – Surge Protection Devices – They are now a requirement as part of the 18th edition regulations as it protects against surges into the electrics from outside the building. These are usually caused by lightning strikes, but can be caused by power surges from elsewhere down the electrical network. When this happens to your domestic fuse board it can be devastating to your home’s wiring. SPDs are installed between the outside feed and the main switch in your consumer unit and will trip if any inward surge is detected.
AFDD – Arc Fault Detection Device – Arc Fault Devices were created for scenarios when and if the current is high enough, electrical currents jump the gap between two conductive materials. Arcs can reach temperatures of up to 5,000 degrees and are the reason for just over half of the domestic house fires within the UK. Reasons for this include damaged cables from rodent damage, degradation, crushed cables, loose connections and installations by unqualified people/cowboys. AFDDs are likely to become mandatory in the near distant future as further protection against fires caused by faulty domestic wiring.
What type of consumer unit do I need?
There are four types of consumer units. The most common are the main switch consumer units and the dual RCD consumer units.
Main switch consumer unit
This type of board is and should be the most common consumer unit being installed today. They are also the best type of consumer unit to choose to completely comply with 18th edition regulations. The major benefit of choosing a main switch consumer unit is you populate it with RCBOs and these devices give you individual protection of each electrical circuit. The majority of electrical contractors will recommend installing a main switch consumer unit following on from the 18th edition wiring regulations, as these boards are versatile and can be installed with RCBOs, surge protection devices and MCBs.
Dual RCD consumer unit
Dual RCD boards are supplied with a main switch and two RCDs. Consideration must be given to circuit design in this scenario. You should not, for example, put all the lighting circuits on the same RCD as if a fault ever occurs then the RCD will turn off the whole bank of MCBs it’s protecting. This will mean you will be in complete darkness whilst trying to resolve the issue.
RCD incomer consumer unit
These boards are predominantly used in garages and sheds. The big difference between this type of board and others is it doesn’t have a main switch. The main way to isolate this type of board is via a single RCD.
High integrity consumer unit
This type of consumer unit is manufactured with three neutral bars, which effectively gives you three sets of circuits. In layman’s terms, there is more flexibility with what electrical circuits you will have controlled from each bank. The option gives you the best of both worlds between an RCBO (main switch) and a dual RCD consumer unit, as it allows you to have two banks of MCBs and one entire bank of RCBOs, for your mission-critical circuits. Ie: fridge, freezer, fish tank etc
How do the main types of consumer units vary?
Amendment 3 Consumer Unit
This is the most common consumer unit. These are metal and normally have a front lid hinged at the top, the size is completely dependent on the number of circuits you are having. (10 way, 14 way etc).
Duplex Consumer Unit
These are the big boys – a consumer unit on top of a consumer unit! This type of board is usually supplied as a main switch option only but there are RCD options out there if you look hard enough. Duplex consumer units have become more and more popular since amendment changes in the last few years and because of the improved knowledge of circuit separation (RCBOs).
Flush Consumer Unit
Even consumer units are now stylish! These flush boards are becoming the new trend. They install seamlessly into modern homes and are less bulky. The only difference here is the appearance, in terms of all the necessities (main switch, busbar) they are all the same.
Garage Consumer Unit
This type of board is anything under four ways… most of the time. They are commonly used in outhouses, sheds, and garages, where a couple of circuits may be required for lighting and tools.
EV Consumer Unit
With people making the move towards electric cars, EV charging consumer units will become more and more popular. Manufacturers are now releasing standalone EV consumer units that can be added to new and old dwellings. These EV boards are most commonly supplied with a 100A Main Switch, and Type 2 Surge Protection and should be populated with RCBOs.
Things to look out for
If your house still has a plastic consumer unit installed, then look carefully for any cracks around the housing of the unit or if you can smell burning/ hear crackling sounds (This could be arcing). If any of these signs are present, call a fully qualified electrician ASAP!
If your consumer unit is tripping continuously then there is obviously a problem with one circuit or more. Again in this scenario, it is very important you call a fully qualified electrician to sort out the issue immediately
To check that your whole house’s electronics and wiring are safe you should have a periodic inspection every 10 years, carried out by a.. you guessed it! Fully qualified electrician!
It is also good from time to time to just open the lid to your consumer unit and check there are no signs of overheating.
Can I replace my consumer unit myself?
Unless you are a fully qualified electrician, then you should not under any circumstances try to replace your own consumer unit. It is a legal requirement that this type of electrical work is carried out by a certified professional.
Beyond that, if done incorrectly, you could injure yourself and put both your family and home at risk.
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