The Ultimate Consumer Unit Guide (2022)

Ultimate Consumer Unit Guide

Ultimate Consumer Unit Guide

As every year passes the rules, regulations and technology are updated to improve the electrical industry. The consumer unit is the most vital electrical component inside any home, it controls and distributes power safely and efficiently. More importantly though it protects humans against potential electric shock or death.

This year there was an update to the amendment 2 wiring regulations but before we get to that lets take a look at the consumer unit basics.

What is the consumer unit?

As already mentioned 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, this is due to any potential emergency happening and you may need to turn one of the devices off or back on!

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 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 too, 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 protect appliances from overload. They come in a range of amperages from 6a to 50a in domestic installation. 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 switch boards being preferred because of regulations and safety.
  • RCBO (Residual Current 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. Imagine the home owner adds a circuit of 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. Usually caused by lightning strikes, but can be caused by power surges from elsewhere down the electrical network, when this happens into your domestic fuse board 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 5000 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 main types of consumer unit but the first two we will discuss are the most common you will find being installed these days.

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 to install a main switch consumer unit following on from the 18th edition wiring regulations, as these boards are versatile and can be installed with RCBO’s, Surge

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 all the whole bank of MCB’s its 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 the 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 more flexibility with what electrical circuits you will have controlled from each bank. The option gives you the best of both worlds between RCBO (main switch) and a dual rcd consumer unit, as it allows you to have two banks of MCB’s and one entire bank of RCBO’s, for your mission critical circuits. Ie: Fridge, Freezers, Fish tanks ect.

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 cables exposed.

If your consumer unit looks anything like the above image, call an electrician immediately.

A fuse box looking like this is more common than you think.. sadly.

How do the Main Types of Consumer Unit 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 amount 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 on 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 4 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

In a recent study it is believed that by 2030, half of the cars on the road in the UK will be electric. Quite a stunning fact but proves the importance in the upcoming years to EV Charging consumer units. 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, Type 2 Surge Protection and should be populated with RCBOs.

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 or put both your family and home at risk. “”Do you have an electrician finder or something similar you can plug here for yourselves? Something like the link to the below..””

What Are The Amendment 2 Wiring Changes?

Amendment 2 of the 18th Edition IET Wiring Regulations (BS 7671:2018) were announced at the end of March 2022. The previous amendments (BS7671:2018+A1:2020) will be withdrawn at the end of September 2022. In this article we will look at the changes in these regulations.


  • The removal of the risk assessment – This will mean that the installation of surge protection devices can no longer be decided via a calculation.

The removal of the special dispensation for single dwellings. They are now to be considered along with all other electrical installations.


Protection against transient overvoltages shall be provided where the consequence caused by overvoltage could:

  • Result in serious injury to, or loss of human life, or
    • Result in failure of a safety service, as defined in part 2, or
    • Result in significant financial loss or data loss

For all other cases SPDs shall be fitted to protect against transient overvoltages, unless the owner of the installation declines such protection and wishes to accept the risk of damage to both wiring and equipment as tolerable. The requirement to install SPDs where the consequences could result in serious injury to, or loss of human life is the same as previously stated in amendment 1. Where we see a big shift, is in indent two, which requires an SPD to be installed where the consequences could result in the failure of a safety service as defined in part 2.

BS 7671

BS 7671 defines safety services as: “An electrical system for electrical equipment provided to protect or warn persons in the event of a hazard, or essential to their evacuation from a location. This will mean that any distribution board supplying electrical equipment that would fall in to the definition of a safety service, as described above, will require an SPD. Therefore, now that domestic installations are not exempt from these requirements, a smoke alarm that is supplied from a consumer unit, rather than a battery, must be protected by an SPD.


Indent three is similar to the previous requirement where an SPD should be installed where commercial or industrial activity could be interrupted, the requirement now is that an SPD shall be provided where the consequence caused by overvoltage could result in significant financial or data loss. This leads on to the final requirements of the regulation

The basic position of section 443 is now that SPDs shall be installed. In practical terms, most installations will have distribution boards that require surge protection due to the indents above, so it would only be distribution boards that did not require surge protection, as no circuits outlined in regulation 443.4.1 were present. Then a discussion is encouraged between the electrical designer and the client to ensure that no unacceptable losses occur from overvoltage, while also considering the requirements to protect against switching overvoltages from regulation 443.4.2.

Regulation 443.4.2. – Protection against overvoltages shall be considered in the case of equipment likely to produce switching overvoltages or disturbances exceeding the applicable rated impulse voltage of equipment according to Table 443.2, e.g., where inductive or capacitive equipment, such as motors, transformers, capacitor banks, storage units or high current loads are installed.

Section 443 details where surge protection devices need to be installed, however, what is not clear is the type of device required. Generally, type 2 SPDs will be used for most installations but type 1 devices will be needed in certain circumstances:

For all other circumstances, a type 2 device will be sufficient to provide adequate protection for distribution boards. Where protection against overvoltages is required for specific equipment, a type 3 device may be used to provide protection.


Regulation 712.443.101 – Where protection against transient overvoltage is required by section 443, such protection shall also be applied to the DC side of the PV installation. When the inverter incorporates an SPD, it is only considered as fulfilling the SPD requirement if the manufacturer specifies its use for the DC side of the PV installation, otherwise, it will need an external SPD. Varistors included in the inverter are not considered an SPD.

This will mean that if the electrical installation requires surge protection to be fitted to comply with section 443, as discussed above, SPDs would now also need to be installed on the DC side of the installation to protect both the PV panels and the inverter. Surge protection devices designed for the use on the DC side of a PV system are designed to a different standard than SPDs used in low voltage installations. Although they are still described by using type 1 and type 2, as explained above, where type 1 devices are to

protect against direct lightning, it is extremely important that only devices designed for use on the DC side of a PV installation are used. All SPD’s installed on the DC side of a PV installation shall comply with BS EN 61643-31. Generally, the SPD will be a Type 2, unless the building has an external lightning protection system.


Regulation 514.16.1 – The presence of SPDs in an installation shall be indicated by an information notice at or near the relevant distribution board(s). The requirements of this regulation need not be applied for domestic (household) premises or similar simple installations where the information is recorded on the appropriate certification for initial verification, complete with Guidance for Recipients as detailed in Appendix 6, and issued to the person ordering the work.

We hope this information was useful. Information Supplied by

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