3 things you must not forget while changing a consumer unit

Quite a number factor is responsible for changing of electrical consumer units or CUs. Some of those include the following:

  • The MCB is blown and the replacement is out of the market.
  • An old property has an equally old consumer unit that is now obsolete and no more complies with the latest regulations.
  • The building is undergoing a rewire, refurbishment or massive renovation.

Whichever may be the cause to change a consumer unit, it is crucial that you as an electrical contractor should keep in mind the following four things while doing the job. Here we go:

The client is NOT a qualified electrician

These days accessing information is easier than ever thanks to the Internet and Google. Thus many ordinary folks do their research and gather information that they think are helpful in showing their knowledge and intelligence to an electrician. It is important for electrical contractors to remember that at the end of everything the clients are not qualified electricians. They do not possess the knowledge, skill sets and hand-on experience that are necessary to replace a consumer unit. So basically they are absolutely unaware about the practical issues that crop up during such replacement works.

As an electrical contractor, you must encourage customers all the time to get an EICR or Electrical Installation Condition Report done before replacing the CU. This addition work ensures the replacement job complies with the latest regulations. The EICR test report also provides an additional help in such circumstances, says a qualified tradesman with years of experience in install and replacement of consumer units. Drawing insights from the report it becomes easier to both design and select the protective devices for the new consumer unit that is just installed.

It is a good idea to educate your clients about the level of protection needed under the BS 7671. This will allow you design a foolproof solution that complies not only with their requirements but also budget and expectations.

Now the question is how are you going to educate them? Let us explore that in the following paragraphs.

As far as the UK wiring regulations are concerned every circuit has to be shielded from both the following:

  • Residual current or earth leakage and
  • Overloads

Residual current is the fault that results in electric shocks. It can result in heavy injury as well as fatality or death. On the other hand overload is the fault that results in fire in cables and damaged appliances.

The circuit protection devices

Let us start with examples; the most common circuit protection devices are RCD, MCB and RCBO. RCD is the full form of residual current device. It protects a bunch of circuits from earth leakage or residual current. MCB is the shortened name of mini circuit breaker. It safeguards a given electrical circuit from current overloading and fault currents. RCBO is residual circuit breaker with overload. It is the combined aspects of both MCBs and RCDs. The device protects a given circuit from residual current as well as overloads. It is obviously the most costly item among circuit protection devices.

Different types of consumer unit

There are a number of determinant factors that play their roles while you look for the ideal consumer unit to install in your home. The factors include:

  • The total number of circuits to handle
  • Circuit types
  • Budget constraint

Consumer units come in three distinct categories.

  • Fully loaded
  • Main switch
  • High integrity

Fully loaded consumer units

This variety of the product is widely seen because of the affordable cost and reliability. It is made up of dual RCD boards completed with MCBs. The variety is best suited for smaller homes or buildings that have limited circuits that are complex. Some of the examples of this particular range of the product include:

  • MK: 10 way (K7666SMET), 15 way (K7668SMET)
  • Hager: 6 way (VML733H), 10 way (VML755), 12 way (VML766), 16 way (VML716)
  • Contactum: 10 way (DDS10166MS-PO1), 12 way (DDS12188MS-P010), 16 way (DDS16166MS-PO1)
  • Wylex: 10 way (NHRSS10SSLHI), 15 way (NHRS15SSLHI)

The flip side of fully loaded consumer units is that both the configuration flexibility and circuit separation that they offer are highly constrained or limited. Even some of the boards at the height are found to be completely fixed. There is just no way for high priority circuits like Hager VML 755.

Main switch consumer unit

Experts unanimously consider it as one of the best solutions for circuit protection that are available. It provides a total circuit separation. However the flip side is it is too costly. The variety comes only with the main switch and enables every circuit to be protected by the RCBO mechanism. Interestingly the consumer itself is never very costly. Its installation adds up to its overall cost. You get this variety of consumer units in a wide variety of sizes ranging from 5 to 40.

High integrity consumer unit

This variety of consumer units is steadily rising in popularity. The solution blends the best aspects of a dual RCD unit as well as main switch consumer unit. Also known as HI consumer unit it is composed of 3 neutral bars and comes with a pair of RCDs. It allows 2 banks of MCBs and a bank of RCBO for circuits having high priority.

In other words, standard circuits like ring finals and lighting are provided with commensurate residual current protection while high priority circuits are given total circuit protection. This variety of consumer units first made their appearance about ten years ago and was available only in larger duplex arrangement of more than 20 ways. These days a large number of electrical manufacturers have this product in the market. Moreover the models that are now available are as small as 10 ways which provide both homeowners and qualified electricians great flexibility not only in changing a consumer unit but also in designing circuits at pocket-friendly cost.

Based on the information above getting the right consumer unit for your home will not be a big challenge any more. However if you want it is always better to consult your electrician over the matter.