Choosing a Consumer Unit
- Circuit Protection Devices
- The Main Types of Consumer Unit
- Other Consumer Units
The Consumer Unit or fuse board is the most important electrical safety device in the home and workplace. It fulfills two vital functions:
- Protecting cables (and subsequently appliances) from overload which can cause fire, and
- Protecting humans from the electric shock caused by earth leakage
All households are different - from one bedroom apartments in the city to large country houses and all of them use electricity in different ways: Some have electric showers, some have electric hobs, others have tropical fish tanks, some have outdoor lighting and water pumps while others have workshops with machinery...
For this reason, there is no such thing as a 'standard consumer unit' - but while the number of sizes, makes, brands and combinations of configurations is almost infinite there are in fact only four main types of consumer unit.
Used in conjunction with the circuit protection devices - (RCD, RCBO & MCB) - these four types of consumer unit offer the homeowner and electrician huge flexibility of circuit design and budget. It is important to understand that in most domestic properties it would be possible to use any one of the four types of consumer unit, the decision being governed by budget and attitude to circuit separation.
Circuit Protection Devices
Before we dive into the consumer units, let's briefly look at the devices:
Isolates the entire consumer unit and all devices. Turning this switch to 'OFF' will cut power to all circuits that are terminated in the consumer unit - which is usually all circuits in the house. Nearly all consumer units are supplied with a 100a main switch.
RCD - Residual Current Device
Protects a bank of circuits from earth leakage or 'Residual Current' - for example - cutting through the lawnmower cable. Protecting a bank of MCBs means that earth leakage on one circuit will cut power to all other circuits protected by that RCD and is considered a form of 'nuisance tripping'. The most common domestic RCD is rated at 80Amp 30mA. Click here if you want to know more about RCDs.
MCB - Mini Circuit Breaker
Protects cables and devices from overload and consequently fire. Under the latest '18th Edition Wiring Regulations', all MCBs must be used in conjunction with an RCD in order that the circuit is also protected against earth leakage.
MCBs are commonly available in the following amperages: 6a, 10a, 16a, 20a, 32a and 40a. Click here if you want to know more about MCBs.
RCBO - Residual Current Breaker + Overload
A special device that combines the functionality of both RCD and MCB, protecting against both overload and earth leakage. This offers complete circuit separation negating nuisance tripping.
Click here if you want to know more about RCBOs
SPD - Surge Protection Device
This device is now a requirement as part of the 18th edition regulations as it protects against surges into the system from outside the property. Usually caused by lightning strikes, but can be caused by power surges from elsewhere, these surges into your domestic fuse board can be devastating to your homes 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 Faults are where, if the current is high enough, electrical currents jump the gap between two conductive materials. Arcs can reach temperatures of up to 6000 degrees and can be the source of over half of the domestic house fires in the UK. Reasons for this include damaged cables from rodent damage, degradation, crushed cables, loose connections, and more. AFDDs are likely to become mandatory in the future as further protection against fires caused by faulty domestic wiring.
Click here if you want to know more about AFDDs
The Four Main Types of Consumer Unit
Main Switch Consumer Unit
A 'Main Switch Consumer Unit' is so called because it is supplied empty of all protection devices except the main switch. Whilst it may be populated with an RCD and MCBs.
It is usually populated exclusively with RCBOs as shown in our image, but theoretically could be populated with RCD and MCBs.
Many electricians consider this the best circuit protection solution as each circuit is protected from overload and earth leakage individually, thus preventing nuisance tripping caused by earth leakage on other circuits.
Following the latest amendment to the 18th Edition Wiring Regulations, Main Switch Consumer units are now commonly populated with Type 2 Surge Protection Devices as standard. Of these boards, the FuseBox F2014MX is proving to be a very popular fuse board. It features 14 usable ways which can be populated with Type A RCBOs or the latest Arc Fault Detection devices (AFDD).
A 'Dual RCD Consumer Unit' is supplied with the main switch and two RCDs and offers a cheaper solution. Our image shows a typical installation with the two banks of MCBs protected from earth leakage by the 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 an earth leakage fault on one of those circuits will cut power to the whole bank, leaving you without any lighting.
Despite the limitations of dual RCD consumer units, they remain extremely popular due to the cost. Indeed, most 'fully loaded' consumer units are dual RCD configurations.
High Integrity Consumer Unit
With three neutral bars, which in essence gives three banks of circuits - A 'High Integrity Consumer Unit' offers the best of both worlds...
Allowing for the use of RCBOs and two banks of MCBs they offer total circuit separation for critical circuits and highly cost effective protection for standard circuits.
High Integrity consumer units are becoming increasingly popular with electricians - because they make circuit design easy - and homeowners - because they offer excellent protection without breaking the bank. They are particularly good in projects requiring 12 or more circuits.
RCD Incomer Consumer Unit
An 'RCD Incomer' consumer unit is a special type of protection device, generally used in workshops, garages, garden offices, and sheds that use small numbers of circuits.
The defining difference between this and other types of consumer units is the fact that it does not have a 'Main Switch'. Isolation of the board is handled by the single RCD. In other words, all incoming electricity is managed by the RCD - hence the name.
This type of consumer unit offers no circuit separation as it may only be populated with MCBs. Earth leakage on every circuit in the arrangement is dealt with by one RCD. That means that a residual current fault on any circuit will knock out power to all other circuits. For this reason, they are almost never used in the main dwelling.
How the Main Types of Consumer Unit are Deployed
Standard 'Amendment 3' Consumer Unit
The most common enclosure is the standard surface mounted, metal, 'Amendment 3', enclosure. All four types of consumer unit are most commonly supplied in this format. They usually always feature a front lid hinged at the top, so that it closes through gravity when not being worked on, thus ensuring it is always closed. Width is dependent on the number of circuits, but they are usually about 240mm high and 110mm deep.
Duplex Consumer Unit
Duplex consumer units which are also known as double bank are a type of consumer unit in which the circuits are arranged over two rows. Duplex consumer units have seen a rise in popularity in recent years with the growing trend in circuit separation. It is important to note that this does not necessarily mean the unit offers two banks of circuits. The majority duplex of sold are 'Main Switch' consumer units which are populated with RCBOs over two rows and connected using a 100A DIN rail connector. Duplex boards are also available in 'High Integrity' or 'Dual RCD' variants.
Flush Consumer Unit
Flush consumer units are one which is recessed into the wall. All four main consumer unit types are available in flush versions. They are functionally the same as a standard amendment 3 enclosure but are aesthetically better with a very slim profile.
Garage Consumer Unit
..is simply a trade term given to any consumer unit below four way - but usually, just two ways - commonly used in outhouses, sheds, and garages, where a couple of circuits may be required for lighting and tools.
IP Rated Consumer Unit
IP rated consumer units are a more specialist unit for wet areas such as outdoor spaces, pools, and spas. We supply two IP rated consumer units and an empty enclosure: The main options are supplied in 10 way variants, one with a 100a main switch, which would be populated with RCBOs, and one with an RCD incomer designed for use with MCBs.
EV Consumer Unit
With the rising number of electric vehicles available, manufacturers have had to provide new ways of protecting both the user and vehicles. As such companies such as FuseBox have released standalone EV distribution units that can be added to new and existing properties. These units are most commonly supplied with a 100A Main Switch Isolator, Type A Double pole RCBO with or without Type 2 Surge Protection.
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