What is a Consumer Unit?

Modern Fuseboards, Mains Boards, or now commonly referred to as Consumer Units (C.U.) generally consist of three components:

• A Main Switch, this does not act as a safety device and is just there to manually turn off the power to your home.
• An MCB for each circuit. Instead of old rewirable fuses, you now have MCBs (miniature circuit breakers), basically a switch which automatically switches itself off when it detects that the circuit is overloaded, i.e. a 6amp MCB will switch off when it detects anything over 6 amps on its circuit. No rewiring of the fuse is needed, when the fault has cleared, you simply switch it back on. MCBs are much more reliable, easier to use and safer than old rewirable fuses. It is not unknown for old rewirable fuses and their fuseboards to set on fire or explode, spitting out molten copper and tin, when certain types of extreme faults occur.
• And an RCD.

What is an RCD?

RCDs (Residual Current Device). RCDs do not detect whether a circuit is overloaded or not, rather, they detect the integrity of the circuit. If there is damage to a cable, water where there shouldn't be or a faulty appliance, an electrical current will flow where it shouldn't do. If you was to receive an electric shock, the shock could kill you before the circuit is overloaded, so an MCB does not always offer you complete protection, Additional Protection is needed. By detecting these fault currents even when they are minute and by having a very quick disconnection time, RCDs protect you from electric shock, or at the very minimum injury from electric shock.

When is a RCD required?

New requirements set in the 17th edition regulations state that there should be RCD protection for, sockets, the electrics in your bathroom or shower room, circuits intended to supply mobile equipment outdoors and for cables buried in walls. Since the wiring in most of the homes up and down the country runs underneath the plaster of the walls, it means every circuit in your home should be RCD protected.

What types of Consumer Units with RCDs are there?

There are three main ways to install Consumer Units with RCD protection:

• Dual RCD Consumer Units often referred to as 17th edition Consumer units. These are the most commonly installed in domestic premises:
  • The consumer unit has one main switch, two RCDs and an MCB for each circuit.
  • The circuits are divided in to two, one group of circuits for each RCD, i.e. upstairs sockets, downstairs lights, and the cooker will be protected by one RCD and downstairs sockets, upstairs lights and the shower will be protected by the other RCD. This reduces the potential of hazards when the RCD trips, so if the RCD with the downstairs lights trips at night, you still have power on the downstairs sockets, therefore you could see where you are going from the use of table lamps.
• Consumer Units with RCBOs.
  • RCBOs are MCBs and RCDs combined together.
  • The consumer unit has one main switch and one RCBO for each circuit. When you have a fault on one circuit only that circuit's RCBO will trip, and not half the circuits as would happen with a Dual RCD Consumer Unit.
  • The draw back is that RCBOs are expensive, approximately £40 each, thus making having a consumer unit installed with this method expensive.

  Customers are rarely recommended to go down this line, as the 'pros' do not outweigh the cost in domestic settings. Sometimes it is hard to find a Dual RCD Consumer that fits in a confined space, so if your existing consumer unit is located in a tight space and your home only has a relatively small amount of circuits, this option provides a solution. Also some people have reasons why it is important to reduce the risk of interruptions to the supply of certain circuits, i.e. having a work office at home or having medical equipment at home etc, In this case a consumer unit with RCBOs may be the best option.

• Consumer Unit with an RCD acting as a main switch.
  • In most cases not the best option since when a fault on one circuit occurs all your power will go off.
  • But often a cost effective solution to match the needs of a small flat, i.e. a studio flat or small one bedroom flat/apartment, where there is a likely to be only one tenant, or small living area, and very few circuits.

Reasons to have your Consumer Unit Replaced

• Simply wanting to improve the standard of safety in your home and to protect yourself and/or your family
• If you ever have electrical work carried out in your home such as having new lighting, shower or socket circuits, and you don't want to have new consumer unit when it is needed, the electrician will have to install a separate smaller consumer unit so that the newly installed work meets current regulations. Not only will this make the job relatively expensive, it will lead to you having multiple consumer units in your home and the possibility of having to pay for further smaller consumer units in the future. The ideal solution, would be to have a new consumer unit installed at the earliest opportunity, i.e. when having an electric shower installed or having a new kitchen fitted, and one that incorporates all the circuits in your home and also has a little space left to add more circuits in the future if you ever decide to have more electrical work done.

Common issues that arise when having a new consumer unit installed in an existing installation

• New regulations stipulate that the 'Main Bonding Conductor', that is the green and yellow (sometimes just green) cable that runs from your electric meter or consumer unit to near you gas meter and main water stop-tap, has to be 10mm in thickness. Many houses still only have a Main Bonding Conductor that is only 6mm in thickness, some no Bonding Conductor at all, in both scenarios a new 10mm green/yellow Bonding Conductor needs to be installed. This is compulsory when a new consumer unit is to be installed, so please don't feel put of by any electrician who tells you that they have to upgrade your bonding when replacing your consumer unit and that it will cost more.
• Also, often the 'tails', they are the cables that run from your electric meter to your consumer unit will need upgrading. Many electricians will automatically work this into the quote they give you without making an issue from it, but you may get someone who will highlight it in there quote (If they do highlight it in their quote and the sum of money is high, be suspicious).
• The only upgrades to the wiring and accessories in your home that an electrician 'must' do when installing a new consumer unit are install new main bonding conductor and tails, when required. Naturally most electricians will give you recommendations as to how you can improve the electrics in your home, but they shouldn't be pressuring or fooling you to have work done, i.e. I know of person who was told because they had sockets in their skirting board they needed to be rewired as it was against regulations even though the plug tops and flexible cords had plenty of space, this is complete nonsense. Even if there was a regulation against sockets in skirting boards, when having a consumer unit installed you don't need to have every aspect of your home upgraded so that it complies with current BS 7671 regulations.
  
  I believe in simply installing the new consumer unit (and main bonding conductor when needed), instead of potentially deterring customers away from having a new consumer unit installed by trying to get them to have more work done. The result is that even though your home may not completely comply with current regulations, your home will certainly be a safer place with a new Consumer Unit, which is why the regulations exist.
• Installing a new consumer unit that has an RCD into an older existing installation, can sometimes lead to further work. This is due to the sensitivity of the RCD. For example, there may be a minute fault that has always existed on one of your sockets that has never been detected before, but which the new RCD will detect. In some cases the wiring may simply be too old and deteriorated so having a new consumer installed is not practically possible without a great deal of work, which will bring up the issue of whether your home should be completely rewired or not.

NICEIC and ESC recommends

In an ideal world and something that NICEIC and ESC recommends is to have an electrician carry out a Periodic Inspection Report before having a consumer unit replaced. The report will highlight any existing faults or problems, if there are any, which will make it clear from the outset what work needs to be done. This avoids the situation were by a customer agrees a price with an electrician to have their consumer unit replace only to be told later that more work needs to be done which the customer needs to pay more for, naturally leading to a situation where either the customer is very suspicious of the electrician's motives (more money) or the electrician can not satisfactorily complete the job and certify their work due to lack of funds on the customers behalf.

elec's method of installing a Consumer Unit

It is natural that a customer does not wish to pay for a full Periodic Inspection work before having a consumer unit installed, apart from being an expensive process; this is only the 'ideal' process.

Once a customer has shown their interest and intention in having a new consumer unit installed, a visit to the premises is required where the job can be sized up and priced for. As well as being able to determine which consumer unit will suit your needs, a visual inspection will be carried out at the same time. A good electrician should be able to judge from a visual inspection whether many problems will occur when a new consumer unit is installed. A visual inspection comes free of charge. Whilst a visual inspection will not unearth all potential faults, it will certainly go a long way in determining whether a serious problem or incompatibility exists. It is also important not to forget that when a new consumer unit is to be installed, it has to be inspected and tested along with all the circuits it supplies in order for a Domestic Installation Certificate to be issued. Therefore, the processes of the inspection and tests will most likely uncover any dormant faults, such as terminal screws that need tightening, slight damage to cables behind sockets etc. In most cases these small problems can be swiftly rectified by a good electrician, and in the case of myself will be rectified as a matter of course at no extra charge.