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Please read the disclaimer before attempting any electrical work. If you are uncertain then contact a qualified electrician.

How to install a consumer unit

Do not attempt to remove, replace or interfere with any consumer unit unless you are you are qualified to Part P regulation standards.. It is an offence to interfere with any of the electric boards seals on the electricity meter. All wiring and connections to the consumer unit must be checked and tested by a qualified electrician.

Link to part p competent person

A modern consumer unit complying distributes electricity via MCB’s(miniature circuit breakers) throughout the home, This is the centre where all the wiring/cable goes back to.

Firstly you should be aware there are 3 methods/boards available, there are single load (rcd), split load(rcd) and RCBO

Single Load Consumer Unit Split Load Consumer Unit RCBO Consumer Unit

(Click the images to view products above)

All of the above comply with the 17th edition, but different benefits differ between the boards.
The single load RCD consumer unit- if in the unfortunate case there is a fault on a circuit then you may be without any power at all (e.g. a fault on the sockets could leave you without your lights, cooker, smoke alarms and shower)

upstairs sockets
downstairs sockets
downstairs lights
upstairs lights
cooker
smoke alarms
kitchen sockets
shower

As they are very sensitive, it is not practical to fit one RCD to protect the whole house

The split load RCD consumer unit-if in the unfortunate case there is a fault on a circuit then you may be without any power on 1 side of the board e.g. if you had :

Left hand side of consumer unit
Right hand side of consumer unit
upstairs sockets downstairs sockets
downstairs lights upstairs lights
cooker smoke alarms
kitchen sockets shower

if there was a fault on your upstairs lights you may be without all of the highlighted circuits in red
“This is the most common consumer unit my customers ask for as the cost is very reasonable compared to the RCBO, its more practical than the single load and if you separate the circuits like above you are always left with some power on every floor ” Jamie Vernon - Online Electrical Services Ltd

RCBO consumer unit-if in the unfortunate case there is a fault on a circuit then you would only be without power on the 1 faulty circuit e.g if there was a fault on the upstairs lights then everything else in the home would remain on:

upstairs sockets
downstairs sockets
downstairs lights
upstairs lights
cooker
smoke alarms
kitchen sockets
shower

Single load consumer unit- The power on the consumer unit coming in is taken through a double pole switch to a RCD and then to a separate live buss bar. Each, MCB, is clipped onto a DIN bar and the "teeth" of the buss bar are inserted into the bottom of the MCB's. The cables to the house circuits are connected to the top of the MCB's.

Split load consumer unit -The power on the consumer unit coming in is taken through a double pole switch to both RCD’s and then to 2 separate live buss bars. Each, MCB, is clipped onto a DIN bar and the "teeth" of the buss bar are inserted into the bottom of the MCB's. The cables to the house circuits are connected to the top of the MCB's.

RCBO consumer unit- The power on the consumer unit coming in is taken through a double pole switch and then to a live buss bars. Each, RCBO, is clipped onto a DIN bar and the "teeth" of the buss bar are inserted into the bottom of the RCBO. The cables to the house circuits are connected to the top of the RCBO. RCBO’s also have an earth and neutral attached which must be connected to the correct terminals.


A: Neutral terminal block for RCD righrt side of the unit
B: Neutral terminal block for RCD left side of the unit
C: Earth terminal block (takes both sides of unit)
D: Main double pole isolating switch.
E: Generally 80 Amp RCD with 30mA (milliamp) sensitivity.
F: Generally 63Amp RCD with 30mA (milliamp) sensitivity.
G: Neutral link cable from main switch to top of RCD
H: Neutral link cable from 80A RCD to neutral terminal (right hand side)
I: Neutral link cable from 63A to neutral terminal block (left hand side)

The RCD is not just a on - off switch but a very important sensitive safety device. They cut off the power when there’s a fault in a fraction of a second, It also detects any imbalance between Live and Neutral conductors which is essential for Class 2 double insulated equipment.

RCDs can be bought in different current ratings and various sensitivities to current leakage, you will need to check which ratings are appropriate for your home.

Old main switch consumer units don’t detect a neutral to earth fault (which means the neutral conductor has contact with the earth conductor) when the new 17th Edition RCD consumer units are installed you may find some circuits will not HOLD/power up, this is because some where in the home this has happened and in some cases can be quite a pain to locate.

The use of RCDs is necessary to meet the needs of the regulations. To protect any socket which may be reasonably expected to supply equipment outside the house or special locations ( lawn mowers, outside lights, bathroom etc). also to protect every cable in the house that is buried in the wall (excluding cables mechanically protected and at a depth of more than 50mm)


RCDs have a test button which creates an earth leak with a resistor, most recommended that they are tested quartaly. There should be a sticker on the consumer unit explaining this. RCDs can be manually switched and can also take the place of the isolator switch/main switch if they break live and neutral (double pole).

MCBs now conforming to the international equivalent of our old imperial ratings (Renard current rating).. the following fuses should be replaced:

OLD FUSE SIZE
NEW MCB SIZE
5 amp 6 amp
15 amp 16 amp
20 amp 20 amp
30 amp 32 amp
45 amp 40 amp

 

Picture above shows the live (J) and neutral (K) coming into the main double pole switch from the meter. These cables are called the main tails, and in this instance, the size of the tails depends on the main fuse size, for a 60A main fuse 16mm sq is substantial, for a 100A main fuse 25mm sq is substantial. in this case 25mm sq tails have been used. This will vary and you should always check with a qualified electrician.


The picture above shows the earth cable from the meter (L). This screws into the earth terminal block.
Picture of a cable entering board.


The picture above shows how a circuit cable is introduced to the unit protected by the right hand RCD (80A). In this case it is a 1.00.mm lighting cable. The live (M) is fixed into the top of the MCB (P), while the neutral (N) goes to the Right hand side neutral terminal block. The earth (o) is in the number 1 terminal (which has been left unsheathed for clarity only always place earth sleeve over the earth ).

The picture above shows how a circuit cable is introduced to the unit protected by the left hand RCD (63A). In this case it is a 1.00.mm lighting cable. The live (S) is fixed into the top of the MCB (T), while the neutral (R) goes to the left hand side neutral terminal block. The earth (Q) is in the number 6 terminal (the earth has been left unsheathed for clarity only always place earth sleeve over the earth ).

Each circuit cable is fed into the consumer unit and connected to the appropriate amp/MCB rating, in this case 6Amp for the lighting circuit.

The above picture shows the MCB clipped on to the DIN rail/bar. The live terminal of the RCD and MCB are then connected tightly to the buzz bar.

Always remember to stick all warning lables on the consumer unit

IMPORTANT: This installation, or part of it, is protected by a device which automatically switches off the supply if an earth fault develops.

Test quarterly by pressing the button marked "T" or "TEST". The device should switch off the supply and should then be switched on to restore the supply.

If the device does not switch off the supply when the button is pressed, seek expert advice.

This label should only be added if there are new and old colours inside the consumer unit.

CAUTION

This installation has wiring colours to two version of BS 7671.

Great care should be taken before undertaking extension, alteration or repair that all conductors are correctly indentified.

Always identify each individual circuit.

 

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