Consumer Units - Buying Guide
Consumer Units Explained: Breakers, RCD Types, and Surge Protection
When buying a consumer unit, it’s important to understand what the protective devices inside it actually do. Modern boards include several different types of protection, each designed to deal with a specific electrical fault.
An MCB (Miniature Circuit Breaker) protects the cable on a circuit. If too much current flows due to an overload or short circuit, the breaker trips before the cable overheats and becomes a fire risk. MCBs are commonly used on lighting circuits, socket circuits, and fixed appliances.
An RCBO combines two forms of protection in a single device. It acts as an MCB for overload and short-circuit protection, but it also includes residual current protection to guard against electric shock. In most modern installations, each circuit is protected by its own RCBO. The advantage is that if one circuit develops a fault, only that circuit trips instead of shutting off large sections of the house.
An AFDD (Arc Fault Detection Device) is designed to detect dangerous electrical arcing. Arcing can occur when cables are damaged, connections are loose, or insulation begins to fail. Because arcing can start fires without drawing enough current to trip a standard breaker, AFDDs provide an additional layer of fire protection. They are required in certain higher-risk buildings such as HMOs, care homes, and student accommodation, and are often recommended for bedroom circuits or timber-frame properties.
Another key consideration when choosing protective devices is the type of RCD protection. Older installations often used Type AC devices, which respond only to simple alternating current faults. Many modern appliances, however, produce small DC components that these devices may not detect properly.
For most homes today, Type A protection is considered the minimum standard. These devices detect both standard AC faults and pulsating DC currents produced by equipment such as LED drivers, washing machines, computers, and induction hobs.
Type B protection is used in more specialised situations where smooth DC fault currents may occur. This is typically required for equipment such as solar photovoltaic systems and some electric vehicle chargers, unless the charger itself already includes built-in DC fault detection.
Surge protection has also become an important part of modern consumer units. Under the 18th Edition Wiring Regulations, surge protection is generally required unless a formal risk assessment determines that it is unnecessary. A Surge Protection Device (SPD) protects electrical equipment from sudden voltage spikes caused by lightning activity or switching events within the electricity network.
Type 1 SPDs are used where buildings have external lightning protection systems or are supplied by overhead lines.
Type 2 SPDs are the most common choice for domestic properties and protect against switching surges coming from the grid.
Type 3 SPDs provide additional protection for particularly sensitive equipment such as servers or high-end audio-visual systems and are normally installed alongside a Type 2 device rather than replacing it.
The internal layout of the consumer unit also affects how faults impact the property. A board with a main switch and individual RCBOs is generally the preferred option. Each circuit has independent protection, so a fault on one circuit does not shut down the rest of the installation.
A cheaper alternative is the dual-RCD or split-load board, where circuits are divided across two RCDs. If one RCD trips, everything connected to that half of the board loses power.
When purchasing a consumer unit, there are also a few practical points to check. Domestic units must now use a non-combustible metal enclosure rather than plastic. The board should include the busbar and blanking plates for any unused ways. It is also wise to choose a unit with spare capacity — around 25% additional ways — so that future additions such as EV chargers, solar systems, or heat pumps can be installed without replacing the entire board.