The Consumer Unit Fuse Box, The biggest Q & A on the internet!

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1) What is a consumer unit fuse box?

A consumer unit fuse box is the ‘brains’ of an electrical system. It is a square or rectangular enclosure found in nearly every home. It contains many switches and devices that control various aspects of your electrical system and will enable you to turn off certain parts of your home electrics whilst leaving other parts energised and working.

The consumer unit fuse box is commonly found, under the stairs, in the garage, near the front door or in the front room of the property along with the incoming supply cables and metering equipment. It could be located elsewhere in the property depending upon age and installation location chosen by the installation electricians. 

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2) What is the difference between a consumer unit and fuse box?

The fuse box is the older style of consumer unit. Rather than containing trip switches and other modern electrical equipment it contains fuses or fuse wire carriers. Each fuse will protect the cables in a certain part off your electrical system. Smaller fuses are typical for lighting and alarm systems whilst larger fuses protect the cables that power the sockets and cooker for example. 

Fuse wire carriers are normally a removable item that contains a fuse wire. Each fuse carried is often a different colour to indicate that it should be wired with the appropriate thickness of fuse wire. Wiring fuse carriers with the incorrect wire can be very dangerous.

The consumer unit does not have fuses or fuse wire carriers but will have switches instead. Each of these switches has a specific purpose and will protect the cables that control the electrical equipment in your home.

(Fuse box pictured left and consumer unit pictured right)

Smaller rated switches tend to protect the lights, smoke detectors and alarm system wiring and larger rated switches will protect electric showers, plug sockets and other high demand circuits. 

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3) What does a consumer unit do?

The consumer unit is the ‘control centre’ of any electrical system. It received the incoming supply cables from your electric meter and splits the electrical supply into usable circuits. It protects each of these circuits using different switches. 

The switches are designed to trip before electrical cables become overloaded or catch fire. In some cases, there are switches that also monitor electrical current flow and trip when some electrical current goes missing. These switches protect us all from electric shock.

The consumer unit also, to a degree, will offer some electrical fire prevention. The most modern type of consumer unit now contains ARC FAULT DETECTION DEVICES which sense when there is electrical arcing occurring in a circuit and turn the circuit off.

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4) What are consumer units made from?

The consumer unit fuse box has been made from different materials over the years. The most modern units are now all made from metal (2023 - 2024) in accordance with wiring regulations which require units to be made from a non-combustible material. 

Older units are made from plastic (a few were metal also) which is not necessarily dangerous but just no longer compliant with wiring regulations. When electrical issues occur and overheating happens as a result, plastic would sometimes melt and provide a source of fuel for any fire that started.

Very old fuse box style units were produced with a plastic front but wooden back. They were then usually mounted onto a wooden surface as well providing plenty of fuel for any fires that started. Despite this, they are not normally considered a danger unless there is evidence of loose connections, overheating or thermal damage.

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5) When would a new consumer unit be required?

There are many instances where a new consumer unit may be required:

• Thermal damage or beyond repair damage to consumer unit.
• Signs of overheating.
• Where a new electrical circuit is required but parts for the consumer unit are obsolete.
• Where an electrical inspection highlights that the existing consumer unit is inadequate or dangerous.
• Where a rewire is being carried out in a property.
• When there is no space in the existing consumer unit for a new circuit.
• When the consumer unit or its equipment has become water damaged.
• Where the electrical rating of the consumer unit is exceeded by the electrical demand of the property (addition of electric showers, car chargers, extra circuits etc).
• Where corrosion or mechanical damage has made the consumer unit unsafe, cracks, breaks, missing covers and failing internal components.

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6) What is needed before a new consumer unit is changed?

The condition of the electrical system and its earthing and bonding must be suitable for the new consumer unit to be installed. Without ascertaining the condition of the current system, it is not sensible of advisable to install a new consumer unit. There may be existing hidden electrical faults that are presently not detected by older consumer unit or fuse box technology that will be detected by the new consumer unit. 

In these cases, circuits may not be safe to energise once the consumer unit is installed and may need to be left disconnected until the faults are rectified. In some cases, the consumer unit may not even TURN ON if it is not happy with the condition of the present electrical system. 

For these reasons, most electricians will carry out a PERIODIC ELECTRICAL INSPECTION before the new consumer unit is to be fitted. This inspection will produce an ELECTRICAL INSPECTION CONDITION REPORT which will outline any issues that need attention, any serious and minor defects AND whether the existing system is suitable for a new consumer unit. 

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7) Are old Electric Fuse Boxes Illegal?

Simply because a consumer unit fuse box is old does NOT mean it is illegal. In fact, there are many fuse boxes that are still in use today and working. They should be regularly maintained and inspected by a professional to ensure that they can continue to provide safe continued service. 

Older fuse boxes or consumer units would, in many cases, simply not comply with current wiring regulations (2023-2024 18th Edition BS7671 Amendment 2), as safety wiring regulations are updated often leaving older units failing to comply. 

Failure to comply with current wiring regulations does not necessarily make something illegal unless it is also a breach of EAWR 1989 or introduces serious electrical danger. 

What it does mean is that, you are unlikely to be able to ask an electrician to add on to an older or non-compliant electrical system until it is brought up to modern safety standards. The expense of this will vary with the age and condition of your wiring system and the best way of ascertaining the age and condition is the periodic electrical inspection.

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8) What are the components inside a CONSUMER UNIT FUSE BOX?

The photograph below shows a consumer unit fuse box, there are several electrical components within this box, each performing a different job and responsible for different safety aspects.

This box looks fairly new but is now an older style consumer unit and more modern electrical equipment is available that offers more convenience in the event of a fault.

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9) Linked Main Switch

The linked main switch is named so as both the LIVE (Natural and Line) conductors are broken together when the switch is operated, it is also physically linked on the switch portion at the front of the device.

This is visible to the far right of the consumer unit. It is a device that isolated the electrical supply to the entire consumer unit box and makes it safer for an electrician to carry out maintenance or repairs inside the consumer unit. It also will allow the complete isolation of the consumer unit and its connected circuits in the event of an electrical emergency. 

This switch should not routinely be used to turn the electrical supply on and off. If complete isolation is required to the circuits contained within this unit, then each of the circuits switches and RCD devices should be switched off one by one. This should start with the individual circuit switches, then the RCD, RCB, RCCB devices and finally the main switch. 

Turning the electrical installation off by the MAIN SWITCH without unloading the circuits is likely to cause excessive wear and tear on the main switch as it attempts to break and reinstate a larger electrical load. 

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10) RCD

The RESIDUAL CURRENT DEVICE is responsible for monitoring the electrical circuits current flow. It detects when there might be some electrical current missing from the circuit(s) it is monitoring and will disrupt the supply to those circuits under such circumstances. 

Its purpose is to prevent electric shock within the electrical installation. The assumption is that missing electrical current is flowing through a person whilst they are receiving an electric shock. For these devices to be effective, they must be 30mA (thirty milli amps) devices. Any higher than 30mA will not be considered to be providing electric shock prevention. 

30mA is the level beyond which serious injury and death may occur as a result of a shock, hence these devices are set to this level or slightly below to ensure that any electric shock is minor and the period of which is limited to milliseconds. 

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11) MCB

The MCB or Minatare Circuit Breaker is there to protect the cables on each electrical circuit that it controls. These devices sit on the copper busbar and are rated to different electrical currents, beyond which they will turn off protecting the electrical system from overload and fire. 

6-amp MCB devices will typically protect the lower powered circuits such as home security systems, lighting, smoke detectors and other small devices. They will trip immediately when detecting large fault currents but will trip more slowly if the rated current of 6 amps is slightly exceeded.

MCB devices are manufactured in 3 trip types. B curve, C curve and D curve. The B curve devices are the most sensitive and will trip instantaneously at 3-5x their rated maximum current. The C curve devices are more suitable for commercial applications and will trip instantaneously at 5-10x their rated current and the D type are more suited to Commercial or Industrial settings as they are the least sensitive and will trip at 10-15x their rated current. 

More information regarding these types of devices can be found by consulting each manufacturer, SCHNEIDER manufacture electrical components and have more information regarding their devices.

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12) Copper Busbar

The copper busbar is responsible for moving the electrical supply from each of the RCD devices or Main Switch to the circuit breakers. In the consumer unit fuse box pictured above we can see that there are two copper busbars. There is one for each RCD device.

Copper is used as it is electrically conductive and reasonably inexpensive. There are more conductive metals that would also do the job but the cost is much higher hence the copper is a popular choice. We can see from the photograph below, there is a copper busbar that is not sitting quite right due to different switches from different manufacturers being installed.

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13) Neutral Bars

In this consumer unit there are three neutral bars. Each of the RCD devices has their own neutral bar for the neutral wires of their circuit to connect into. The final neutral bar is for any standalone RCD devices such as RCBOs (combined MCB and RCD device) to connect into. This is the most versatile set up in some cases.

The neutral wires connect into the neutral bars by means of a screw. The screw head are special heads that require an electrical terminal screwdriver referred to as a ‘slotted pozi’ or ‘terminal’ driver. 

The neutral bars and screws are often constructed from brass which is significantly stronger than copper, less expensive but also less conductive. It is about the best material that fulfils all criteria required in order to make sound electrical connections that last. 

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14) M.E.T Earth Bar

The Main Earthing Terminal or M.E.T is the point at which all of the circuit protective conductors (earth wires) connect to the Earthing conductor of the electrical system. It is often here that the safety electrical bonding connections will also connect. Main Equipotential bonding is the safety earth electrical connection to metal pipework. This is often required in electrical installations. The M.E.T, like the Neutral bars is also generally constructed from brass as this material offers the best trade-offs between mechanical strength, electrical conductivity, and cost for its intended purpose.

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15) Incoming tails

The incoming tails are thick cables, usually copper, that connect the electric meter for the property to the consumer unit or main isolator. These ‘tails’ are responsible for carrying the burden of electrical current for the entire electrical system, and as such, they should be considerably thicker than the rest of the wiring inside the CONSUMER UNIT FUSE BOX as we can see from the photograph above. 

Your electrician will ensure that these cables are of adequate thickness for the power demands of your home should you choose to have a  PERIODIC ELECTRICAL INSPECTION carried out.

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16) How many different brands and models of consumer unit are there?

There are quite literally dozens if not hundreds of brands of consumer unit that are currently installed in our homes. Some of these brands are no longer manufactured and parts are obsolete and some are still manufactured today. 

Within each brand there may be two or three different models of consumer unit which the electrician installing the unit will decide on. 

Some of the most popular brands on the market today appear to be: Axiom, British General, Chint, Click Scolmore, Contactum, CPN, Crabtree, Deta, Eaton,Europa, Elucian (Click), Fusebox, Hager, Hamilton, Honeywell (MK) Lewden, MK (Honeywell), MCG, M2, Niglon, Proteus, Schneider Electric, Verso amd Wyle.

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17) Can you still obtain parts for older consumer unit fuse boxes?

Certain manufacturers that are still producing consumer units have made sure that their parts are predominantly backwards compatible. HAGER are a manufacturer of consumer units and they seem to have great backwards compatibility with their older units. Despite the parts no longer being available for older units, newer parts tend to fit into older consumer units which is fantastic for cost savings despite a higher initial investment than some cheap brands. 

It is always important to contact the manufacturer of the specific consumer unit fuse box direct and consult with their technical department prior to attempting to install new equipment into older units. Compatibility characteristics need to be checked for safety reasons before any parts are installed. 

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18) Can older consumer units be repaired?

This will depend on the condition of the consumer unit and its age. The electrician will also need to make a judgement call on any other issues that may be found. 

If a unit is showing signs of thermal damage affecting the Neutral bars, Main Earthing Terminal of the enclosure itself then generally it is best to replace the unit. If there is damage to the circuit breakers (MCBs), RCDs, RCBOS, or Main Switch then these can normally be sourced and replaced assuming that the correct parts or suitable manufacturer recommended replacements are available. 

Certain repairs are not possible if overheating or fire has occurred and not only will the consumer unit itself need to be replaced but potentially the cabling in the electrical installation as a whole should be replaced. A periodic electrical inspection will help determine the extent of repairs to the consumer unit or electrical installation.

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19) Are old consumer units dangerous?

Any consumer unit can be dangerous. In terms of interfering with equipment, consumer units and fuse boxes should not be worked upon by those without sufficient qualifications, knowledge, and skill to safely carry out works. 

As fuse boxes and consumer units age, so does the switchgear inside them, the electrical connections, and the wiring. Electrical installations should be periodically inspected to check for defects and to ensure that the installation is in suitable condition for continued use. 

Certain older units can contain asbestos which in itself can present a danger if disturbed. There are wooden backed consumer units from many decades ago, which under the right circumstances can become a danger or fire risk and even poorly installed or defective modern consumer units can also be dangerous.

Whilst the answer to this question is not particularly helpful from the point of view of immediate knowledge or self-checking, the answer is always to have an electrician carry out a periodic inspection for you as this and only this will determine the relative safety of a consumer unit or wiring installation. 

The photographs below show an older style consumer unit. This unit has been ‘upgraded’ from fuse wire carriers to insertable circuit breaker switches but it is still a very old unit nonetheless. 

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20) Can you put a new fuse box on old wiring?

There are many older wiring installations that are suitable to have a replacement consumer unit fitted. There are more modern wiring systems that should be replaced before any new consumer unit is fitted. 

The key to knowing if it’s possible to replace the consumer unit with the existing wiring is to have a periodic electrical inspection carried out on your electrical system. This will highlight any defects that are present and produce an EICR which will show you, in-depth, the extent of the remedial work needed. 

Remedial works should be completed prior to any consumer unit being fitted. Without this there can be no electrical certification for the work as it will not comply to the safety wiring regulations. 

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21) Do plastic fuse boxes need to be replaced?

A plastic CONSUMER UNIT FUSE BOX DOES NOT need to be replaced simply because it is plastic. Whilst the current edition of the wiring regulations (18th Edition Amendment 2 BS7671) states that all enclosures should now be of non-combustible material, it does not necessarily mean that plastic units present a danger or should be replaced. 

If a plastic consumer unit is showing signs of thermal damage, mechanical damage or other noticeable safety concerns exist then YES, it should be replaced. 

If you are unsure of how suitable your current fuse box or consumer unit is then contact a trusted electrician for their recommendations.

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22) Can you sell a house with an old fuse box?

A house can always be sold at the right price and having an old fuse box will not necessarily make it any more difficult to sell your home. A buyer might be put off by the potential cost of repairing an aging electrical system however, and may wish to negotiate on the asking price so they can bring the electrical installation up to date. 

Old fuse boxes indicate that the wiring is also at least of the same age. Whilst wiring is often suitable for continued use for several decades, fuse boxes should be updated regularly to provide the most up to date safety and protection for the occupants of the home. 

It is becoming more common when buying and selling homes to have an electrical inspection carried out by an electrician to establish the condition of the electrical system prior to sale or purchase.

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23) Can I change a fuse on a consumer unit?

There are certain electrical jobs that are OK to carry out a DIY basis. Swapping a BS1361 Cartridge fuse in a consumer unit is a straightforward job and usually involves minimal risk. The manufacturer’s instructions for your consumer unit or fuse box should be followed to ensure that the task is completed correctly and safely. 

Replacing a fuse wire in a fuse carrier can be more of a risk as there is more to go wrong. Poorly wired fuses can leave live fuse wire protruding from the fuse carrier and present a risk of electric shock.

The correct wire also needs to be selected for the rewiring of the fuse carrier, too large a wire can result in the fuse not blowing before cables are damaged or catch fire and too small a fuse wire can mean that fuses blow too often. Using the incorrect type of wire can also lead to electrical danger. Manufacturers information should be sought and if in doubt, contact an electrician to advise or replace the wire for you. 

Replacing an MCB on a consumer unit is NOT a job for DIYers to undertake. There are safety electrical checks and other considerations when swapping out an MCB. Only an electrician is safe to undertake this type of task.

We can see in the photograph that this consumer unit has several different brands of equipment installed. This is not likely to be safe, however parts are now obsolete and no longer available. The safest option is to replace this consumer unit for a new one. 

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24) What are the symptoms of a bad fuse box?

There are many different symptoms of a bad fuse box, these are not limited to, but can include the following:

• Buzzing noises.
• Intermittent power cuts.
• Fishy or burning smells emanating from the fuse box.
• Cracks or holes in the fuse box.
• Cracked or damaged switches.
• Sparking or flashes from the fuse box.
• Crackling or popping noises from the fuse box.
• Flickering or Dimming Lights.
• Tripping GFCI or RCD devices.
• Circuit Breakers / MCB switches tripping.

Some of the above symptoms are not specific to a bad fuse box and could also be as a result of other electrical issues in the home. If you are experiencing any of the above issues then you should consult an electrician to investigate the problem for you. 
It is not common for an entire fuse box to go bad unless there has been excessive heat, burning or smoke damage inside. It is more likely that there is a component or area of the fuse box that has been affected. Any damage to a fuse box may result in the requirement for the entire box to be replaced for safety reasons. 

The consumer unit pictured below has a large gap where fingers can be inserted for a potentially deadly electric shock. This unit is BAD. Minor repair needed from an electrician. 

The equipment is fairly modern and replacement parts are still available so the repair should be possible and straightforward.

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25) Why would a fuse box not work?

If there is no power in the property AT ALL then it is possibly the result of a failed fuse box, or more specifically the incoming cables and Main Switch. Only this part of the fuse box failing would mean that the whole fuse box would not work. 

The first thing you should check when this happens is that it is not a problem in the street or further afield. You can call the local distribution network operator (DNO) on 105 to ascertain if there are any local power supply issues that may be affecting your home. The number is freephone in the UK and will put you through to your local DNO for your area. 

If the DNO reports no issues then it may be that your fuse box is not working. An electrician will be able to safely investigate the problems for you. There could be an issue with the electric meter, the incoming meter tails to the consumer unit or the main switch itself. 

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26) Can a fuse box go bad in the house?

A fuse box can go bad in your home when no maintenance has been carried out or the fuse box has become very old. Electrical connections work loose over time with heating and cooling due to expansion and contraction of the different metals. When connections become loose this causes high resistance and excessive heat eventually resulting in damage or small fires. This can be prevented by having an electrical check carried out regularly. 

The main cause of a whole fuse box going bad is the Main Switch failing. This can fail internally to the switch, on the terminations of the incoming mains cables, on the top of the main switch or the copper busbar and neutral connections on the bottom of the Main Switch. 

The photograph below shows and old fuse box that has gone bad. Loose wiring and lack of maintenance has caused a small fire to start in the fuse box. This led to a full house rewire as the old wiring was not suitable for a new consumer unit.

Various components within the CONSUMER UNIT FUSE BOX can also go bad individually causing power outage and failure of plug sockets or lights in your home. 

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27) How do I know if my fuse box needs replacing?

The absolute best way to know if your fuse box needs replacing is to contact an electrician. Even old fuse boxes may be ok if there are no plans to extend or alter wiring but only an electrician can tell you if the box needs to be replaced. 

Sometimes an electrician can tell from a photograph if the fuse box is VERY old or in poor condition visually, but generally, even an electrician will have to visit your home and carry out ELECTRICAL TESTING in order to tell you if your fuse box is ok along with your home electrics. 

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28) How much does it cost to replace a consumer unit?

This will vary between areas in the country and the company carrying out the work but typically consumer unit prices will be from £400 for a garage consumer unit replacement up to £1500 for a very large home with many electrical circuits. Includes supply, fit, testing and certification.

These figures are estimates and will generally exclude required pre-inspection and testing to check for hidden electrical problems and will also exclude the cost of any remedial works that are required. 

More important than the cost of a replacement consumer unit is to ensure that the contractor you use is highly recommended, will talk you through the process and provide you with the certification that you need once the work is completed.

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29) Is it worth replacing a consumer unit?

Updating an aging consumer unit or fuse box is always a worthwhile investment but you may want to consider if spending the money is worth it in your circumstances.

If your home is old and may soon require a rewire then having a new consumer unit installed now may be a waste of money if yet another new one is required in a few years when the rewire is undertaken. 

If you are selling your home and an old consumer unit may affect the selling price then it might be best to get it installed and ensure that you have all the electrical certification to go with it proving that the electrical system is in good condition along with the brand-new consumer unit. 

If your consumer unit is 5 years old or less then it is probably not worth replacing it unless there is a compelling reason to do so. Such reasons could be for instance, damage to the old unit, the need for more electrical circuits for new equipment or to move the consumer unit from its current location to a new location. 

Before considering a consumer unit replacement it is a very good idea to have an electrical inspection carried out to make sure the wiring will take the new unit without problems. 

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30) Is it easy to replace a consumer unit?

It is a technically difficult job to carry out the require testing and inspection process before installing a new consumer unit. Any faults that are identified during the testing and inspection process require specialist knowledge in order to rectify and will likely come at additional costs. 

The process of removing the old consumer unit from its current position involved great care and skill to avoid any damage to circuit wires before the new unit is installed. 

When the new unit is installed, there is yet more testing to carry out to ensure that the electric shock protection devices are working as the manufacturer and wiring regulations intended and to ensure that all connections are torqued in accordance with the manufacturer’s instructions. 

(The photograph shows an older consumer unit needing to be replaced and part way through testing and fault finding)

Wiring the new consumer unit involves great skill and care to ensure that no wiring is trapped, crushed together and to ensure that all circuits are easily identified for future fault finding or testing purposes. 

Replacing a consumer unit professionally, skilfully and with the correct certification is one of the more difficult jobs that an electrician will undertake. 

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31) Is it illegal to replace your own consumer unit?

Electricians replace their own consumer units all the time so it is not illegal to replace your own consumer unit. Anyone other than an electrician replacing their consumer unit is likely to fall foul of the law regarding the wiring regulations and electricity at work regulations however. 

Non-Electricians will not have sufficient knowledge to ensure the right equipment is installed in the correct manner, nor will they have the correct tools or expertise to correctly torque connections and carry out fixed wire testing to ensure compliance with BS7671. 

Failure to carry out these procedures when replacing a consumer unit is likely to be illegal along with failure to notify building control of the change of consumer unit. For more information on this you should contact your local building control department in the territory you are in. 

For the UK more information can be found HERE. 

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32) How long does it take an electrician to replace a consumer unit?

An electrical inspection prior to the installation of the consumer unit typically takes 2 to 4 hours depending upon house size, quantity of electrical circuits and obstacles in the way. 

Assuming no remedial works are needed following the electrical inspection then the removal of the old unit takes around an hour to carry out without damage whilst ensuring that circuits are labelled correctly.

The new consumer unit installation takes around 2 to 3 hours plus another hour or so of electrical testing once installed. 

All in all, the process takes at least a full day, done properly with all testing and paperwork completed but the process is usually split over two different days as electrical inspections often throw up minor or major electrical issues that require repairs before the new consumer unit can be safely and legally fitted and certified. 

More information on pre testing before consumer unit can be found HERE.

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33) What is the life expectancy of a consumer unit?

Certain manufacturers offer a ten year warranty on their consumer units and switchgear against manufacturing defects. This would seem to indicate that there is a degree of confidence that their products will last at least ten years but likely longer or else they would be snowed under with warranty repairs. 

That being said, as a company we rarely come across issues with consumer units that are less than 15 years old and most problems tend to occur with units that are 20 years old or more. Even then it could be that loose connections have caused component failure rather than the manufacturers equipment itself. 

It’s fair to say that if your CONSUMER UNIT FUSE BOX is OVER 20 years old you should consider having it replaced. Not only will you benefit from up-to-date electric shock protection, fire protection, more modern equipment, and a full electrical inspection but you also severely reduce the chances of an old consumer unit failing and leaving you in the dark one night. 

(The photograph above shows a Main Switch that had failed in a consumer unit leaving the occupants in the dark for several hours)

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34) What is the law on consumer units?

Any new consumer unit installed within a domestic premises must have their enclosure manufactured from a non-combustible material, or be enclosed in a cabinet or enclosure constructed of non-combustible material.

The consumer unit must also be arranged such that there is sufficient space for initial installation, later replacement of components, accessibility for operation, inspection, testing, fault finding, maintenance and repairs. 

The above information is from BS7671 18th edition 2nd amendment wiring regulations where the exact wording can be found. 

Any new consumer unit that is installed must also be notified to building control and a compliance certificate obtained along with the production of an electrical installation certificate from the installing electrician.

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35) Do you need building regs to change a consumer unit?

Yes. Building control will need to be notified in advance of this type of work so they can arrange a visit to check the compliance of the work carried out. Replacing a consumer unit is considered notifiable work under the Part P section of the building regulations. 

If you choose to use an electrician that is part of a competent person’s scheme then they will have the ability to self-certify their work as compliant and issue a compliance certificate for you along with the electrical installation certificate for the new unit. 

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36) Do you need a certificate for a consumer unit?

Yes, two in most cases. 

If the new consumer unit is installed in a domestic dwelling, then it will not only require an Electrical Installation Certificate but also a Building Control Compliance Certificate. 

The Electrical Installation Certificate is typically around 5 to 7 pages in length and contains the test results and circuit details for the electrical installation. It details all the testing that was carried out when the consumer unit was changed and the results obtained through the testing. 

The Building Control Compliance Certificate would normally be issued by the electrician that undertook the installation for you. Most electricians are part of a competent person’s scheme and are able to self-certify that their work is compliant with building regulations and issue the certificate on that basis. 

The Electrical Installation Certificate (IET) would look something along the lines of THIS although there are other versions available. The IET (Institute of Engineering and Technology) have produced many different electrical forms for electricians use and the link above takes you to the EIC.

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37) What happens if an electrician does not provide a certificate?

If your electrician does not provide you with the correct certification for any electrical works then it may be difficult to sell your property if you cannot prove the electrical work has been carried out safely. 

Where the safety or suitability of the electrical installation for continued use is in question then we would always recommend having a Periodic Electrical Inspection carried out by an electrician. The report that follows the Periodic Electrical Inspection will outline any safety concerns and give a Satisfactory or Unsatisfactory outcome. 

If you have lost any certification that was originally given then you should contact the electrician that carried out the work as they may have the ability to reissue one for you.

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38) Can an electrician charge for a certificate?

Yes of course. Producing a certificate and documenting electrical work takes time and therefore costs money. The cost is usually built into any quote that you receive for electrical works so may not appear as an itemised line on the quote or invoice. 

If you require an electrical certificate re-issuing that was previously issued and subsequently lost then there may be an administration charge by the electrician for the re-issuance of this certificate. 

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39) What are the sizes of a consumer unit?

In terms of the number of circuits that a CONSUMER UNIT FUSE BOX can hold, the consumer unit sizes range from 2 circuits all the way up to 22 plus circuits. The more circuits that the consumer unit is able to supply the larger the physical dimensions of the consumer unit.

The smaller the physical dimensions of a consumer unit, the less room there is inside for the installer to work and manipulate the cables into their required positions. Electricians prefer larger consumer units for the additional space that is available whilst installing. This additional space not only makes the installation process easier but ensure that there is less chance of shorting out from trapped or pinched cables in an enclosed space. 

Customer prefer smaller neater consumer units as they are less obtrusive in the home and can look ugly if left on show. There is often a compromise as the electrician uses a large unit for the benefit of installation and longevity then the customer has a cupboard built around the consumer unit to cover it. 

If considering building a cupboard around the consumer unit, great care should be taken to avoid drilling into buried cables but also to ensure that the consumer unit has adequate working space around it to carry out maintenance and fault finding. 

When wondering what the physical sizes of the consumer unit are, each manufacturer will list the sizes of each of their units on their website. If you have limited space, talk to your electrician, and see what is possible for your consumer unit installation.

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40) What is a split consumer unit?

A split consumer unit is sometimes also known as a 16th edition consumer unit. These units were typically installed under the 16th Edition of the wiring regulations (BS7671) which ran from 1991 to 2008. The split consumer unit would ‘split’ the electrical installation into electrical circuits that were protected by an RCD and those that were not. 

The RCD protected circuits would typically have been ‘power’ circuits incorporating sockets, cooker, shower, and other similar circuits. The non-RCD protected circuits would typically have been lights, alarm, and doorbell. 

The reason for the split was so that in the event of a fault that the RCD tripping did not disable the lights and security alarm.

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41) What is a Dual RCD consumer unit?

The Dual RCD consumer unit has two RCD devices enabling the electrical installation to be split and protected by two separate devices. The idea behind this is to allow some parts of the installation to remain powered during an earth fault on any circuit. 

The RCD will trip when there is an earth fault and disconnect all circuit that it protects. By having two separate RCD devices, only one half of the consumer unit will have the power supply shut off in the event of an issue. 

This was brought in with the 17th Edition wiring regulations around 2008 and is an upgrade from the 16th edition consumer unit as now all circuits are afforded RCD protection. The photograph below shows an 18th edition consumer unit that is also DUAL RCD. 

(We can see that there are two RCD devices protecting several different circuits in this consumer unit)

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42) What is a 16th Edition consumer unit?

A 16th edition consumer unit would have been installed under the 16th edition of the safety wiring regulations BS7671 commencing around 1991 and running until 2008. The consumer unit typically was a split load consumer unit affording RCD (electric shock prevention device) protection to power circuits but not lighting circuits. 

The units were typically constructed from plastic and are now due for replacement as the regulations have changed twice since making better and safer equipment is now available. The 16th Edition consumer unit is not necessarily unsafe nor would it necessarily fail and electrical inspection but modern electronics have now made the RCD devices in these units obsolete.

Modern electrical equipment in our homes MAY render the RCD device in these units ineffective meaning no electric shock protection in the form of RCD. 

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43) What is a 17th Edition consumer unit?

The 17th Edition consumer unit was installed under the 17th edition of the wiring regulations which ran from 2008 to 2018. This would see early units constructed from plastic and later units constructed from metal. They typically had two RCD devices and later units may have been ‘high integrity’ units with the possibility of adding separate circuits not protected by RCD or protected by RCBO devices. 

The later 17th edition consumer units afforded much more flexibility over the 16th edition and early 17th edition units. These units are mostly new enough that they can have their RCD devices replaced for the modern ‘A’ type devices thus meaning that the whole unit may not need to be replaced should electrical work be required in the home. 

The later 17th edition consumer units mostly had self-closing lids that would drop down over the switches.

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44) What is an 18th Edition consumer unit?

The 18th edition consumer unit was and still is (2023-2024) installed now. The 18th edition safety wiring regulations (BS7671) were brought about in 2018 and are now on amendment 2. 

The latest consumer units will typically have RCBO devices and an SPD device. RCBO stands for Residual Current Breaker with Overload. These are a circuit breaker and an RCD in one device. The ultimate in convenience in the event of a fault meaning that only one electrical circuit will be affected when there is a typical electrical fault in our homes. 

SPD stands for Surge Protection Device. Many 18th edition consumer units come with these installed as standard. Whilst they were mainly optional, many installers fitted these as standard due to their relatively low cost and benefits that were offered to the homeowner and their electrical equipment. 

18th Edition consumer units were and still are constructed from Metal and have a self-closing lid which drops down over the switchgear leaving no switches on show during normal operation. 

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45) What is a high integrity consumer unit?

The high integrity consumer unit is manufactured from metal and has three neutral bars inside. Typically, they came from the manufacturers with two RCD devices and the ability to add RCBO or MCB devices to the remaining spaces in the consumer unit connecting into the third neutral bar. 

These units offered the maximum flexibility of any consumer unit to date and were an improvement over the previous units available. 

They came around sometime whilst the 17th edition safety wiring regulations were in force during 2008-2018. They were manufactured from metal and had a self-closing lid over the switchgear during normal operation. 

Many high integrity 17th edition consumer units are able to be upgraded to 18th edition consumer units with some replacement components and an electrician’s labour. 

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46) What is the latest edition of consumer unit?

At the time of writing (2023-2024) the latest edition of the wiring regulations is the 18th edition amendment 2. This means that the 18th edition consumer unit is the latest edition available. 

The best type would have Main Switch, RCBO devices and a Surge Protection Device (SPD) installed as pictured below.

Manufactured from non-combustible material (typically metal) and with a self-closing lid, these units are the best available units on the market. RCBO devices should be Type A devices (under amendment 2) as standard NOT AC type which were acceptable at the start of the 18th edition. 

These consumer units should be installed by a professional and the correct paperwork issued for the work. You should expect an Electrical Installation Certificate and a Building Control Compliance Certificate from your electrician.

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47) Can you have 2 consumer units in a house?

Yes, you absolutely can have two consumer units in a house. This is very common with older properties that have had electrical installation works carried out AFTER the property was built. 

When older wiring installations are in properties, rather than add on to an older wiring systems, electricians will often test the earthing and bonding in a property then install a brand-new smaller consumer unit that meets up to date wiring regulations. This can be a cost saving measure where a rewire or completely new consumer unit is not wanted but electrical works must still go ahead. Typical situations might be the installation of a new bathroom or kitchen where electrics will be moved around and added. 

It is also common when two properties have been converted into one that there will be two consumer units in the new single property. 

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48) Can you have a new consumer unit without a rewire?

In some cases, yes and in some cases, no.

If the wiring in the property is very old then it is likely that a new consumer unit will detect faults with the electrical system and refuse to turn on. Some faults can be found and fixed whereas others cannot. 

If cabling is very old then the insulation around the copper wiring will likely have degraded badly. New consumer units can detect when there is poor insulation on cabling as electrical current leaks away from the electrical installation. This leakage is detected by modern consumer units and they will simply not work effectively.

You may not need a new CONSUMER UNIT FUSE BOX, talk to your electrician about your requirements and see what they recommend. 

Newer installations (20 to 30 years old) generally withstand the installation of a consumer unit without the need for a rewire whereas older installations may well need a rewire in order to fit a new consumer unit. 

The best way of ascertaining the condition of the wiring in your property is to ask your electrician to carry out a PERIODIC ELECTRICAL INSPECTION to determine what condition the installation is and its suitability for continued use. 

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49) What is a part populated consumer unit?

A consumer unit that is ‘part populated’ is a consumer unit that has some or most of the switchgear already installed or included with the consumer unit. This means that the consumer unit will have the Main Switch, RCD devices, RCBO devices or MCB devices already included. 

There are both advantages and disadvantages with these:

Good:

• Can be more cost effective than non-populated units
• Much more convenient to have everything together
• Saves time on ordering parts from different wholesalers

Bad:

• The rating of each of the devices may not be what is required for the system
• Devices may go unused and waste money
• The installer may require additional parts that are not included

Most electricians will order the required parts individually from a wholesaler these days as part populated units seem to be a little less popular than they were. This is especially the case as we are now switching over to RCBO devices rather than the RCD / MCB combinations from 17th edition.

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50) What is the difference between a consumer unit and an RCD?

A consumer unit contains devices such as RCDs and other switchgear and is the brains of the electrical system.
An RCD is an individual device with a switch that control only part of the electrical installation. Typically, the RCD supplies power to several MCBs (circuit breakers).

It is similar to asking “what is the difference between a car and a steering wheel”. One contains the other and is a part of it.  

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51) How many MCBs does an RCD have?

The RCD can have almost an unlimited amount of MCBs that are controlled by it. There becomes an issue when more and more MCBs are added though. An RCD is able to monitor earth leakage on electrical circuits to decide when someone might be having an electrical shock. It assumes that the missing electrical current is passing through someone’s body, shocking them! 

Every electrical circuit and connected equipment will have varying amounts of natural earth leakage, old cables will also leak electrical current to earth and old appliances too. This gives us an issue with the RCD / MCB setup. The more MCBs that an RCD protects, the more leakage there is likely to be and this can develop into nuisance tripping. 

BS7671 regulation 531.3.2 covers this point. 

(We can see in the photograph a consumer unit with an RCD protecting too many circuits)

The best way to avoid this kind of situation is to have RCBOs installed. These devices are a combined RCD and MCB in one handy little device. As there is now an RCD on EVERY circuit, the chances of excessive earth leakage build up is massively reduced.

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52) Does a consumer unit have to have an RCD?

In domestic settings YES. A consumer unit now MUST have an RCD. There are very few exceptions to this under the 18th Edition Safety Wiring Regulations these days. The RCD is a lifesaving device and should never be omitted from an electrical circuit without good reason. 

In commercial settings it is more common to find electrical circuits and consumer units without and RCD present. There can be equipment in commercial settings that would cause great inconvenience and even safety implications should a minor electrical fault switch it off. 

Very old consumer units may not have an RCD installed. It is not possible to add one to these units as most parts are now obsolete. We also cannot add a standalone RCD device to protect the whole electrical system as this would be non-compliant with the current wiring regulations. 

If your consumer unit is that old that it does not contain an RCD then you should have an electrical inspection carried out with a view to replacing the consumer unit. 

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53) How much does it cost to replace a fuse in a fuse box?

The price for this will vary but at the time of writing we typically charge £90-£180 to replace such a device dependent upon the urgency of the job, the availability of the parts and the brand of the parts. 

Different contractors in different parts of the world and country will charge different amounts so it’s always best to find a couple of trusted contractors that have great reviews and that you believe will do a good job. 

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54) Do old fuse boxes contain asbestos?

Some old fuse CONSUMER UNIT FUSE BOX units will contain asbestos in the form of flash guards for when fuses would blow. They are generally safe if left untouched but if damaged could present a danger. 

If you suspect that your consumer unit contains asbestos then its best to contact your local trusted electrician for advice and assistance. They will be able to assist or signpost you to the right place. 

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55) Why is my consumer unit tripping?

Your consumer unit is tripping because there is an electrical fault somewhere in your electrical system. It’s important not to panic, there is often a simple cause and some fault finding from an electrician is often needed to pinpoint the issue before the repair can be undertaken. 

A lot of customers believe if a switch is tripping then the switch is faulty. This is more often than not., untrue. Switches can go bad but they usually do so after they have discovered and electrical fault and been reset too many times in anger by a frustrated homeowner. If this sounds like you then stop now and call your electrician to come and investigate for you before the problem gets more expensive and inconvenient. 

Various different electrical faults can cause a switch to trip in a consumer unit. Check our BLOG for more information.

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56) Why have a garage consumer unit?

A lot of garages and shed have a CONSUMER UNIT FUSE BOX. This is the best way to supply power to an outbuilding in many cases.

It is possible to get electricity to an outbuilding or garage without having a garage consumer unit but there are advantages to installing one. It is better to split the power in the garage to individual garage circuits such as sockets, lights, automated door opener and potentially outdoor lighting at some point in the future. This can all be achieved with a garage consumer unit. 

The alternative is that the main consumer unit in the house has a circuit allocated to the ‘garage’ and supplies everything. We would then need to fuse down in various places around the garage to supply lights and sockets. If ever there was an electrical fault in the garage, then the entire garage would trip off in the house. 

(The photograph shows a small consumer unit, that which is typically found in a garage)

With a separate consumer unit in the garage, an electrical fault is much easier to find. Further electrical installation work in the future is normally more straightforward and less expensive and a garage consumer unit is generally a more convenient option over a single circuit to the garage. 

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57) Does a consumer unit have to be boxed in?

No. In fact, it’s ideal if it IS NOT boxed in. When joiners and homeowners box in consumer units, they can often create problems. 

Boxing in introduces a risk of drilling through cables in the walls surrounding the consumer unit. This kind of electrical damage may take weeks or months to manifest in the form of a tripping switch, arcing or crackling. When an electrician attends to repair the problem, they may need to destroy the box that has recently been made for the consumer unit in order to gain access to the cables in the wall. 

Boxing in can also make consumer unit access very difficult or impossible in the future. Electrical systems will need to be maintained or accessed for fault finding at some point and a nice neat box around a consumer unit can make removing the cover of the consumer unit impossible at times. 

Think carefully before boxing in your consumer unit. It may be better to have the consumer unit moved somewhere else if the sight of it is an aesthetic nightmare. 

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58) How much does it cost to move a consumer unit?

The cost depends on a number of factors. 

• Where is the consumer unit going to?
• Is the current consumer unit up to date?
• Do you want the extended cables hidden in the wall or in trunking?
• How many electrical circuits are there?

There may be other factors that also affect the price as well. If a consumer unit is brand new, up to date with the wiring regulations and required moving up to 6 inches away then it is possible that no cables will need to be extended and the unit may be able to be moved simply with minimal additional work. Minor certification may need to be filled out for this also. 

If a consumer unit is old, contains many circuits and needs to be moved to the other side of the house it will be vastly more expensive than the first scenario. The electrical system will need all of its circuits tested and inspected £200-350, the consumer unit will need to be replaced £700-£1300, the cables will need to be extended £200-£500 and the work will require an Electrical Installation Certificate along with a Building Control Compliance certificate. 

We can see how costs add up quickly and different scenarios affect different jobs.

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59) How do I reset my consumer unit?

When a switch trips on a consumer unit it is likely because there is a problem. If you have a CONSUMER UNIT FUSE BOX like the one pictured below then there is a MAIN SWITCH that often trips when an electrical fault is present. 

(We can see from the photograph that there is the main switch and several other switches)

Before attempting to reset the Main Switch, you must turn off all the other switches first. Then try resetting the main switch. If the Main Switch stays in the on position with all other switches off then it may be possible to find the issue without an electrician. 

With the Main Switch in the ‘on’ position, turn on each of the other switches with a 3 to 5 second gap in between turning switches on. If the Main Switch trips again, make note of the last switch that was turned on. That switch is likely to control the circuit that contains the electrical fault. 

Turn that switches back off and begin the process again. This time, do not turn on the affected switch. If the Main Switch stays on then you can call an electrician to investigate the affected circuit for you. 

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