The Consumer unit

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The consumer unit (or fuse box as it is often referred to) is the single most important part of your electrical installation. Depending on when it was installed, it will generally house a selection of protective devices that ensure your electricity supply automatically disconnects in the event of a fault. Each circuit within your house will usually have its own protective device, and the system as a whole will be backed-up by a large fuse within the main supply to your house (but we design circuits so that this should never blow!)

There are a variety of protective devices out there, and this section goes through the most common ones found in domestic settings, along with some notable pros and cons:

The humble Fuse. These are everywhere! The vast majority of appliances with plugs on them will have a fuse fitted within that plug, and as we have mentioned above, even new installations still have a large fuse where the supply enters the house as their backup method of protection. Some older consumer units still use rewireable fuse carriers to this day (and they are perfectly functional), so it is possible to find installations solely relying on fuses for protection., although they are not permitted on new installations. 

How do they work? Simply, a piece of wire is connected between the two ends. As current flows through in use, that wire warms up. Depending on the rating of the fuse, that wire will be designed to melt and break the circuit at a set point, protecting the wiring from overheating. 

Pros: Cheap to buy, most types readily available, reliable, no maintenance required.

Cons: Standard fuses need to be thrown away if they blow, rewireable fuses can be fiddly to reset (and spare parts are becoming scarce), and of course you need to keep spares and be able to replace them in the dark (they only blow at night after all!)

The Circuit Breaker. These replaced the need to have the rewireable fuses mentioned above in your consumer unit. If they trip, then they can just be reset with the flick of a switch. Whilst they are being largely superseded now by RCBOs (see below), unless your house has only just been rewired, you will probably have these in your consumer unit. They can still be fitted today, although there are only a few situations in which we do.

How do they work? Rather than using a fuse wire that breaks under high current, circuit breakers use a bi-metallic strip that bends as it heats up. Once it reaches a temperature equivalent to its rating, it will disconnect the circuit - known as 'tripping' - this is then reset by turning the switch back on (once you have rectified the fault of course).

Pros: Cheap to buy, long life expectancy, can be quickly and easily reset, reliable, no maintenance required.

Cons: As with fuses, they don't detect or protect against electric shock on their own. 

The Residual Current Device (RCD): These are designed to detect minute amounts of current escaping to earth - such as a person being electrocuted - and have been mandatory on new installations (particularly socket circuits) for a long time now. It doesn't require much current to kill you - around 50 milliamps (0.05 amps) - but thankfully RCDs fitted in the home environment will trip at less than 30 milliamps. Not all consumer units will have RCDs fitted and this is the leading reason why we get asked to upgrade someone's consumer unit. It is not mandatory to retrofit RCDs, although it is strongly recommended - unfortunately it does usually require a consumer unit change. 

How do they work? They detect the current going in both directions on the circuit(s) in question. The minute that they become unbalanced (such as if someone was being electrocuted), they disconnect the power. 

Pros: They markedly reduce the chance of you being killed by electrocution, cheap to buy, reliable.

Cons: Can be expensive to retrofit, they do require regular testing, they can malfunction and give 'nuisance tripping' - much more likely if you have lots of appliances with complex circuit boards (such as computers, TVs, microwaves etc). 

The RCBO: These are quite simply circuit breakers and RCDs combined in the same unit (Residual Current Breaker with Overcurrent protection). These became popular as we started plugging in more and more complex electrical devices such as computers, TVs, smart home systems etc. If you plug too many of these into one RCD, you will get 'nuisance tripping' - by effectively putting one RCD on each circuit, you reduce the likelihood of this greatly. We install RCBOs as standard now - this is not yet mandated by the regulations but it will inevitably be so. By doing this we are future-proofing installations as our demand for smart technology will only continue. 

How do they work? They basically have a circuit breaker and an RCD combined in the same unit and work as the individual units do above.

Pros: Much less 'nuisance tripping' compared to a standard RCD/Circuit Breaker arrangement, if a fault does occur only that circuit is disconnected (if a socket causes the problem, the lights don't go out for example). 

Cons: Slightly more expensive to install, they do still require regular testing.

The AFDD: The new kids on the block! Arc Fault Detection Devices go one step further - they detect loose connections where electricity is arcing/sparking across a connection. 26% of electrical fires are caused by faulty appliances and/or connections - this is where the AFDD steps in. They are not yet mandatory in houses, but are recommended for socket circuits (where the highest risk appliances are plugged in). They are simply installed instead of an RCBO (the AFDD combines all three functions) and we do recommend these when considering a consumer unit change, if the budget allows.

How do they work? In addition to the functions of an RCBO, the AFDD monitors for subtle changes in the frequency of electricity such as is seen when arcing/sparking is occurring. 

Pros: The safest/most comprehensive protective device available.

Cons: Much more expensive to install, they do still require regular testing, they have an onboard computer chip that consumes a small amount of background power.

The SPD: Surge Protection Devices are not currently mandatory to fit, although are highly recommended (certainly if you have, or plan to install later, an EV charger). We install SPDs as standard (they usually come pre-fitted to the consumer unit) - although we can obtain consumer units without if you would prefer. Their job is to protect your sensitive electrical devices from surges in power supply, such as during electrical storms. 

How do they work? They divert spikes in power back to earth, rather than through into your wiring. 

Pros: Negligible cost, protection of high value items.

Cons: They are deemed to be consumable parts and will require replacement every few years (depending on how often they are activated) - they are not user replaceable but it is a simple job for an electrician.