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Four things to consider when replacing a consumer unit

Posted by Elaine Hammond on 1st August 2018

replacing a consumer unit

There are a number of reasons why property owners change their consumer unit. Perhaps one of the MCBs has blown and replacements are no longer available. Maybe they have taken possession of an old property and the consumer unit is not compliant with current regulations (soon to be the 18th Edition). Or maybe they are undertaking a rewire, refurbishment or larger renovation project.

Whichever is applicable there are four key things the electrical contractor should consider.

1. Your client is not a qualified electrician

The single most important thing for the electrical contractor to remember is that regardless of how much research they’ve done or how intelligent they are, your client is not a professional electrician, has never before replaced a consumer unit and is unlikely to be aware of all the issues.

The electrical contractor should always encourage the customer to have an Electrical Installation Condition Report (EICR), which should be carried out before replacing the consumer unit. This is to establish that the latest regulations are met and will ensure that the contractor isn’t left with faults to clear that were not included in the original contract.

The EICR test results will then help with the design and selection of protective devices for the new consumer unit.

Educating your client regarding the level of protection that is required under BS7671 will help you design a solution which matches their requirements, budget and expectations and need not be any more onerous than briefly explaining the following:

a. In general the UK Wiring Regulations require that all circuits are protected against both:

Overload – the fault which can result in fire in cables and damage to appliances.

Residual Current (or Earth Leakage) – the fault which causes electric shock, which can result in injury or death.

b. The Circuit Protection Devices: RCD, MCB and RCBO. What they are and what they do:

RCD – Residual Current Device

Protects a bank of circuits from residual current or earth leakage.

MCB – Mini Circuit Breaker - Protects an individual circuit against overload and fault currents

RCBO – Residual Circuit Breaker with Overload - Protects an individual circuit from both residual current and overload. It combines the aspects of both RCD and MCB and is therefore more expensive than an MCB.

2. Future proof …like there’s no tomorrow!!

There’s not a single building project in history during which the client did not, at some point, change their mind or the specification. As the project progresses they may change the gas hob to an electric one, decide that they want to put an electric shower in the guest room or decide they want to install a security system.

The electrical contractor must remember this is entirely reasonable and prepare for rather than react to it. Giving yourself plenty of wiggle room at the outset will avoid hassle and wasted effort later in the project when the inevitable happens. Explain at the start of the project that the consumer unit will serve the property for some considerable time and should be able to comfortably handle any changes and additions to circuit layout in coming years.

If during the design the contractor defines 10 ways is required then at the very least fit a 12 way consumer unit. If a 12 ways is required then go for 15, if 16 go for 20 etc.

3. High priority circuits and circuit separation

In order to properly specify a circuit protection solution which fits with the client’s expectations it is vital to ascertain which circuits require special consideration in respect of RCD’s.

Separation of high priority circuits is important because it removes any chance of that circuit being knocked out by an earth leakage fault on any other. This occurs in a standard RCD/MCB configuration when the RCD cuts the power to all MCBs it is protecting upon detection of a residual current fault on one. ..and of course, this problem is exacerbated when a greater number circuits fall under the protection of one RCD.

Common high priority circuits include smoke alarms and security systems but every client will have a different attitude to what constitutes ‘high priority’: the freezer in one home for example, may just be host to some out of date fish fingers, while another household’s freezer contains expensive cuts of venison! Home offices containing PCs, tropical fish tanks, stairwell lighting, swimming pool pumps and heating systems are all examples of high priority circuits.

4. Which type of consumer unit?

A number of factors determine which consumer unit you will ultimately fit, including the number of circuits, types of circuit and client’s budget. The three main models are:

i. Fully Loaded Consumer Unit

Fully loaded consumer unit

This is a popular solution due to its low cost and comprises a dual RCD board supplied complete with MCBs. They are suitable for smaller properties with less complex circuits and are available in a number of ‘ways’, depending on the manufacturer:

Hager: 6 way (VML733H), 10 way (VML755), 12 way (VML766), 16 way (VML716)

MK:  10 way (K7666SMET), 15 way (K7668SMET)

Wylex: 10 way (NHRSS10SSLHI), 15 way (NHRS15SSLHI)

Contactum: 10 way (DDS10166MS-PO1), 12 way (DDS12188MS-P010), 16 way  (DDS16166MS-PO1)

The main drawback with fully loaded consumer units is that they usually offer limited configuration flexibility and circuit separation. Indeed, some of the boards above are entirely fixed with no provision for high-priority circuits, such as the Hager VML755 which offers 5 fixed MCB ways on each RCD and does not allow for the fitting of RCBOs.

ii. Main Switch Consumer Unit

Main switch consumer unit

This is considered by some as the best circuit protection solution available as it offers total circuit separation but there is a cost implication. It is supplied with just the main switch and allows for every circuit to be RCBO protected. Whilst the consumer unit itself is not particularly expensive the installation of RCBOs makes this a premium solution. Such units are available in all sizes from 5 way up to 40 way. Hager and Wylex have a particularly good offering in the larger units over 20 ways.

iii. High Integrity Consumer Unit

High intensity consumer unit

This solution is becoming increasingly popular as it combines the best aspects of a dual RCD unit and main switch consumer unit. Built with three neutral bars, and supplied with 2 RCDs, the HI consumer unit allows for both 2 banks of MCBs and a further bank of RCBOs for high-priority circuits.

This means that standard circuits such as lighting and ring finals are given commensurate residual current protection, whilst high priority circuits are afforded total circuit separation. HI Units were introduced by Wylex about ten years ago and originally were only available in larger duplex arrangements of over 20 ways. Nowadays however, all the major manufacturers offer HI solutions with models as small as 10 ways, offering both the homeowner and professional electrician excellent flexibility over circuit design at affordable prices.

We hope this article helps with your decision making when replacing a consumer unit and we would like to thank Gil-Lec Electrical Wholesalers for supplying the content for this article. 

Categories: wiring regulations, consumer unit, electrical installation condition report, eicr

Quick Question - Should You Fit A Consumer Unit On It's Side?

Posted by Christos Panayiotou on 18th April 2013

This is the first in a weekly series of blog posts intended to pose a question and gather peoples responses before we reveal the correct answer. We want trainees, experienced sparks, domestic installers and anyone else for that matter to answer the question and contribute to the debate.

So our first scenario is this. You are installing a brand new consumer unit in a domestic property but soon realise that the consumer unit is too big to fit in the same space as the old one. It will fit if you turn it on its side (i.e. rotate it by 90 Degrees). So is this OK? Can you mount a consumer unit on it’s side?

So we have had this out there for a week and collected responses which came out as follows. Nearly 80% of people said no whilst just over 20% actually gave a detailed answer:


So what is the answer?

It is a little bit of a trick question. The answer is that you should check the manufacturers instructions. Some units can be fitted on their side and others can not. Of the 22% that answered "Other" all said this as the answer so those people can give themselves a pat on the back.


Categories: consumer unit

Where To Fit A Consumer Unit

Posted by Christos Panayiotou on 10th January 2013

An often overlooked element of fitting a consumer unit is the location where it is placed. Consumer units are famously located in some of the most awkward places imaginable often behind piles of storage boxes, in the darkest corner at floor level! Many of these may well have been fitted before the days of regulations and on replacement will need to be situated in the correct location.


When choosing where to place the consumer unit, thought needs to be given to how the consumer unit will be accessed. Consumer unit locations are notorious for being in the most awkward of places. It is important that it is easy to reach the consumer unit and there is sufficient space around the consumer unit to operate switches and protective devices such as RCDs. It must also be easily accessible for an electrician to access the consumer unit to enable them to carry out inspections and maintenance which may require the electrician to access all connections to the consumer unit. Space is therefore essential! Unsuitable consumer unit locations include enclosures, compartments or other confined spaces.

Consumer unit switches and protective devices within a consumer unit need to be easily accessible to the householder. Access which would require the use of a ladder or similar reaching platform would not be suitable. Thought needs to be given to the needs of the householder particularly if they are disabled, elderly or infirm. In these cases, access to switches and protective devices should comply with BS 8300 – Design of buildings and their approaches to meet the needs of disabled people.

Environmental Conditions

Particularly attention needs to be given to consumer units located outdoors or where environmental factors need to be taken into account. Such locations should always be avoided but if such a location should be necessary, a consumer unit should be of a design appropriate to the situation in which it is to be used. Outdoor locations require weatherproof equipment and weather protection should also be provided to the user.

Preferred Mounting Height

The Part M of the building regulations for England and Wales requires reasonable provision to be made for people to gain access and to use the building and its facilities. Guidance on meeting the requirements is given in Approved Document M. Particular attention needs to be given to Section 8 of approved document M as this includes the objective of assisting people whose reach is limited to use their home more easily by locating wall mounted switches and socket outlets no higher than 1200mm and not lower than 450mm above finished floor level.

Whilst Approved Document M does not recommend a height for new consumer units, the 2013 version of Approved Document P points out that one way of complying with Part M in new dwellings is to mount consumer units so that the switches are between 1350mm and 1450mm above floor level. At this height, the consumer unit is out of reach of young children yet accessible to other people when standing or sitting.

Although this would only apply to new buildings, it is worth giving thought to the mounting height on the consumer unit to so that the consumer unit is out of reach of young children yet accessible to other people when standing or sitting.

When taking all these principles and building regulations into account it comes as no surprise that relocating a consumer unit is work that must be carried out by a Part P Registered electrician who are there to ensure your safety and well being.


Source: NICEIC Domestic Electrical Installation Guide 17th Edition and Approved Document P, 2013 Version.





Categories: consumer unit