In every household, business, or office, where electricity is being used for cooking, for washing machines, water pumps, or for types of machinery, it is most important to install an electrical consumer unit. The consumer unit is necessary for every home and workplace to avoid electric issues caused by earth leakage, overload or short cut, to prevent the spread of fire, and to protect the circuit and premises.

What is a Consumer Unit?

Consumer units, also known as Consumer Box, Fuse box, Distribution Board, or dis-board is an electrical safety device installed in domestic premises to provide control, protection, and distribution of electrical energy to various circuits. The consumer unit has the following components:

1. The enclosure/compartment: The compartment is a box made of steel that serves as a cover to the other components. According to the requirement of the 18^th edition wiring regulations, the enclosure of the consumer unit must be manufactured with a non-combustible material or be contained in an enclosure made from a non-combustible material like steel.

2. The main switch: The main switch controls everything in the consumer unit. The main switch is used to turn off or turn on the electrical supply.

3. The Din Rail: The Din Rail carries no electric current. It is a neutral metal bar that serves as a support to other devices: MCB, RCD, RCBO, Main Switch.

4. The Busbar: It is a long strip of electrical conductor toothed like a comb that is used to lock and connect the main switch to all protective devices in place.

5. Residual Current Devices (RCDs): The RCDs protect and prevents electric shock. It detects an electrical fault by constantly monitoring and measuring the movement of current within the circuit and automatically turns off power to the circuit once it detects an earth leakage.

6. Miniature Circuit Breakers (MCB): Mini Circuit Breaker is to protect wires on electrical installation and prevents electric shock, and also cuts off power automatically once it detects an overload or short cut. The MCB comes within the range of 6amp to 50amp for residential or domestic consumer unit installations and is much higher in commercial settings.
7. Residual Current Breaker with Overcurrent protection (RCBO): The RCBO is a smart kit that does the work of an RCD and MCB. It protects the circuit from overload as wells as protecting it from earth leakage.

When the mini circuit breaker trips, it has detected an overflow of current. For example, a circuit breaker of 10 amperes will trip off if a current of 12amperes flows through it. When this happens, it’s advisable to notify a certified electrician to know what the fault is, before carrying out any work on it or switching it back on. Consumer units in London, and around the UK must provide RCD cable protection to all cables embedded in walls; this is due to the introduction of the 18^th Edition Wiring Regulations. Moreover, the RCBO is mostly used in circuits that are more fundamental or critical to the homeowner like a deep freezer, washing machine, or any lightning circuit.

The Four Main Types of Consumer Unit:

1. Main switch consumer unit
2. Split consumer unit
3. RCD  incomer consumer unit
4. High integrity consumer unit
5. Single phase
6. Three phase

Where Is The Fuse Box?

The fuse box is the primary electrical distribution box that distributes electricity and contains all the electrical control and protection elements. In domestic installations, a fuse box or consumer box is mounted between the electric device and electric meters. Having knowledge of the location of the fuse box within your home or work premises is very important and useful for safety reasons.

What Size Consumer Unit Do I Need?

Before deciding on what size of consumer unit you need, first consider how to choose your electrical consumer unit. First, consider your mounting type and installation location. The consumer unit has the flush-mounted and surface-mounted models, the duplex, garage, and IP rated models. Your installation location will determine the distribution unit model you need. The flush-mounted is recessed into the wall, and functions like the surface mounted but are preferable in terms of appearance.  The garage consumer unit is mostly in outbuildings, while the IP is specifically used in wet areas like pools. Secondly, you should be sure your consumer unit is halogen-free, and confirm its fire resistance temperature.

Your consumer unit should have a structure that helps stop the flow of toxic gases if there should be a case of fire. Now in determining the size of your consumer unit, you should know the kind of element you want to use in the box. Also, your installation space helps to determine the size of your consumer unit. If you prefer to use a 12-modules, which is the width of the mini circuit breaker (MCB), then you can install 12 pieces of a 1-pole mini circuit breaker. The box dimensions should be according to the number of elements you have in your installation. It is advised that you leave extra modules spaces, so you have free space for addition anytime you wish to.

How to Wire a Consumer Unit?

Before wiring a consumer unit, you should ensure that your consumer unit has the basic requirement of wiring regulations which states:

1. The consumer unit enclosure should be made from non-combustible material 
2. Have RCD protection

When creating holes for the cables, make sure that the holes are not larger than they are supposed to be, and that the cable installation method you use should keep up with the enclosure fire containment. Also, your enclosure gaps should not exceed 1mm for the top surface (horizontal) and 2.5mm for the other surfaces. Following the manufacturer’s instructions is necessary.

Wiring a Consumer Unit:

The MCBs should be clipped onto the Din bar and the busbar into a current flowing terminal and tight screwed to give current to the MCBs.Two 16/25mm tail cables, one neutral and the other active are connected to the main double pole switch of the meter. The main earth cable should be screwed into the earth block, and the current-carrying wire should be connected to the MCB from the top while the neutral wire should be connected to the RCD neutral terminal block. Another earth cable goes into the earth terminal block (this earth cable should be unsheathed to differentiate it from the other earth cable). This will give a live charge to the MCB with neutral going to the RCD. It is advisable to get a qualified electrician to do your consumer unit wiring.

How to Replace a Consumer Unit?

Depending on the kind of consumer unit you use, it might need you to first remove the circuit breaker box before disconnecting the wires. In removing the old consumer unit: You should reorganize the wires if required, and if a rubber wire is to be reused, you should be very careful when disconnecting it to avoid damaging the insulators. After removing the old consumer unit, you should run a simple test and checks on the old circuit to identify the issues on the CU. You must label as you go on to avoid getting confused at a point.

Check your new CU

The next thing after removing the old CU is to check and prepare your new CU making sure that all connections are tight and in right place. Fix the CU in place and check that it fit your mounting space.

Connect your supply

Install the connected cables (earth and supply tails) from the meter or switch, using 16mm² for 60/80Amp supplies, and 25mm²  for supplies up to 80/100Amp. Carry out a quick check again to ensure there is no shortage in the supply. Then reconnect the circuit wire following the labels done when reorganizing the wire.

Do labeling

It is easier to avoid confusion if you label it as your work. The mini circuit breakers and the fuses supply to different circuits, and so needs to be labeled to show what circuit they supply. After connecting the circuits, run another check and then go on to screw on the connections again to confirm they are tight and won’t come loose easily.

Reconnect power

Turn off the consumer units and restore the power connected to the CU. Ensure that the individual switches are all turned off before the main switch is turned on, then go ahead to run a full test on the RCD with the right tool.

How to Install a Consumer Unit?

Installation of consumer unit takes four main steps

Step 1: Prepare your installation

Step 2: Prepare the cable

Step 4: Carryout the inter wiring

Step 5: Label your components

How to Isolate a Consumer Unit?

To isolate the consumer unit, you have to first stop the flow of electricity through it. You have to first decide if you want to isolate a particular electrical appliance or a complete circuit. For instance, all sockets are connected using parallel wiring, which forms a complete circuit. If each socket however works independently off the main circuit, then you can isolate the individual appliances.  To completely isolate a circuit and make it safe to work on, remove the electrical fuse from the consumer unit, or flip the trip switch to “off”. If you open the consumer unit cover, you would see the trip switch box (protective device, MCB, fuse). A particular switch trips and turns off the electric supply, if there is an electricity shortage in any of the circuits. You can reset the switch by simply turning it back on.

How to Wire an RCD Into a Consumer Unit?

The Residual Current Device is connected primarily to the consumer unit to prevent any form of electrocution. Before commencing any electrical work, first, disconnect the power supply. Next, connect PE cable (Protective Earth Conductor) to the earth bar, and then wire up cables to the top of RCD. Pay attention when connecting neutral cable. The neutral terminal should be marked somewhere on the RCD. Cut the busbar to the proper length and connect it to the bottom of the RCD and MCBs.If the RCD neutral terminal is on the left, move RCD to the left and reconnect power cables. This way you will still be able to use the busbar. From the bottom of RCD run a cable to the neutral bar. We will have two outgoing cables (twin core and earth). Put earth sleeving over the earth wires and connect them to the earth bar. Brown wires should be connected to the top of MCBs, and blue wires to the neutral bar.

How Much to Replace the Consumer Unit?

The cost for old fuse box replacement or new consumer unit cost varies as it depends on the kind of consumer unit to be replaced, how long the old installation has been, and how many circuits are required for the new consumer unit. In the UK, it can cost about £300 to £400 to replace a consumer unit of six-circuit and around £400 to £500 for a ten-circuit of the consumer unit.