Consumer units and fuse boxes: installation and replacement

What’s the difference between a consumer unit and a fuse box?

Although they serve the same essential function, there are some very important differences between consumer units and fuse boxes that you should understand if you’re considering having one installed or replaced.  

Fuse boxes 

A traditional fuse box was the standard way of distributing electricity around homes constructed in the early 20th century. They kept homes safe from electrical faults and using fuses – safety devices containing a small piece of wire that melts when the current exceeds a specific level, cutting off the electricity to the circuit and preventing damage.  

After a fuse blows, it must either be replaced with another fuse with the same rating or (in the case of rewireable fuses) have its wire replaced to restore your fuse box to full function. 

Consumer units 

Fuse boxes began to be phased out in the mid-20th century in favour of modern consumer units containing circuit breakers, which cut off electricity to the circuit more quickly and don’t need to be replaced after being tripped as they can be safely reset. They offer better safety, functionality, and are compliant with modern wiring regulations.  

If your home still has a fuse box, it’s recommended that you get it replaced with a modern consumer unit. Fuse boxes simply don't offer the same level of protection and performance as their modern counterparts.  

Key safety features of consumer units

Most modern consumer units will contain the following safety features: 

• Main switch – this is your master control for all electricity entering the unit. It allows the electrical system to be safely isolated during emergencies or maintenance work. 
• Residual current devices (RCD) – these immediately switch off the electricity if they detect a fault. They are designed to protect people from electric shocks and earth faults. 
• Circuit breakers – these devices break a circuit when tripped by short-circuit issues or power overloads. They switch off the current faster than traditional fuses, helping minimise damage to wiring and appliances. 
• Surge protective devices (SPD) – these protect circuits and equipment from high-voltage power surges, such as those caused by lightning.  
• Arc fault detection devices – these protect against arc faults, cutting off electricity when an arc fault is detected and preventing electrical fires. 

In some consumer units, you might also find residual current circuit breakers with overcurrent protection (RCBO), which combine the functions of an RCD and a circuit breaker. 

Different types of consumer units

There are five common types of consumer units. 

• RCD main switch consumer unit  

This type comes with an RCD main switch that can safely isolate the entire electrical supply of your home. The RCD provides a single point of enhanced safety for the property, working together with individual circuit breakers protecting each of the connected circuits. 

• Dual RCD consumer units 

These units come with a main switch and two RCDs, which enable the circuits within the property to be divided between the RCDs. This prevents a single fault from disrupting power to all connected circuits. Circuit breakers are installed to provide individual protection to each of the connected circuits.   

• High integrity units

These consumer units provide either circuit breakers or the combined RCD and circuit breaker protection of an RCBO for each of the connected circuits, without combining any circuits together under the protection of a single RCD. 

This offers flexible circuit separation and protection, whilst reducing the impact of a single fault to the disruption of only a single circuit. 

• High integrity split load units 

These consumer units are a combination of a single or dual RCD, together with high integrity protection provided by individual RCBOs. Circuits that benefit from the individual protection of an RCBO are individually protected, while other circuits are divided between one or two RCDs and individually protected by circuit breakers.  

This provides a degree of separation for circuits to minimise the impact of a single fault, whilst also minimising the requirement for individual RCBOs to be installed for each connected circuit.   

• Duplex units

These consumer units are arranged in two rows for the required protective devices and therefore offer a larger capacity for managing multiple electrical circuits. Duplex units are becoming the preferred option for homes with larger electrical requirements and can be provided in any of the above 4 protective device configurations. 

Regulations relating to the installation of a consumer unit

The requirements for the installation of consumer units are defined in BS 7671, the national standard governing wiring and electrical installations.  

A competent, registered electrician will be able to install your consumer unit in line with all BS 7671 requirements; these include: 

• Consumer units in homes must have their enclosures manufactured from non-combustible material or be housed in non-combustible cabinets. 
• They should also be easily accessible, with switches installed between 0.45m and 1.2m from ground level (note, this isn’t always possible in older installations). 
• They should be appropriately protected from dust and moisture. 
• Cables entering the unit must be protected against abrasion and sharp edge. 
• Each installed protective device should be labelled to identify the circuit being protected. 
• Most, if not all, circuits in a home should be RCD-protected to minimise the risk of electric shocks.