Selecting consumer units - a free wall chart from Wylex for Voltimum users

Everyone understands the star rating system for hotels, the classification system that makes it easy to tell at a glance the difference between what a two-star and five-star hotel offers. So why not take this idea and apply it to understanding and choosing the right consumer unit for a project conforming to the 17th Edition of the Wiring Regulations.

Wylex are the market leader for consumer units, and have created Solution 17, a consumer unit rating using those familiar five stars to show what you get from a specific consumer unit assembly. It actually gives a rough guide to seeing ultimate value for money, performance and safety. All types of Wylex consumer units can be installed to the 17th Edition; it's the application of the circuit protection design that dictates how they comply and the resulting levels of protection offered. So, where a two-star hotel is a basic minimum, the minimum standard for a consumer unit says it will comply with the 17th Edition simply by having been fitted with a couple of 30mA RCDs. But there are times when customers may expect or require a lot more.

So what is the Wylex 5 Star Rating?

Let's start by looking at the 17th Edition. Summaries of the new regulations that apply are:

1. Cables concealed less than 50mm deep in a wall/partition that are not mechanically protected by an earthed metallic covering must be 30mA RCD* protected (522.6.6, 522.6.7, 522.6.8.)

2. Every installation must be divided into separate circuits to avoid hazards and minimize inconvenience in the event of a fault, and must take account of the danger that may arise from the failure of a single circuit such as lighting. The possibility of unwanted tripping of RCDs must be reduced (314.1).

3. For parts of the installation that require separately controlled circuits, these must not be affected by the failure of other circuits (314.2).

4. Socket outlets for general use by ordinary persons must be 30mA RCD* protected (411.3.3).

5. All circuits in a room that contains a bath or shower must be 30mA RCD* protected (701.411.3.3)

*NB. 30mA protection may be offered by any mechanical switching device or association of devices, such as a RCBO, RCD or any other equipment designed to open contacts when the residual current attains a given value.

If you had to comply with each regulation in isolation, it is quite easy to meet three of the summary points 1, 4 and 5 with basic 30mA protective devices. But in practice, you have to combine these with the other summary points 2 and 3; it is now you need to apply your electrician's knowledge based on your understanding of the final installation in order to choose the right type of consumer unit, and then come up with the best solution.

What types of consumers units?

So, what types of consumers units are available? There are four generic consumer unit types considered here: main switch, split load, high integrity and dual RCD.

They differ because of the way that they provide 30mA earth fault protection, particularly on independent circuits. When fitted with independent RCBOs, a unit with a main switch incomer complies completely with all five summary points, because this arrangement assures continuity of supply better than any other arrangement; if one device trips because of an earth fault, none of the others are affected

Where any independent circuits are required as in Paragraph 3, dual RCD units can never comply. But that's not to say that 30mA RCD group protection can't be used. Circuits that are protected by a combination of MCBs and a RCD benefit from two-pole protection under earth fault conditions. High integrity and split load units can both comply with Paragraph 3 because they both can accommodate circuits that require independent protection i.e. a 30mA RCBO can be fitted where required.

Wylex star ratings:

What are then the Wylex star ratings for the different consumer unit types? Figure 1 shows how each type of consumer unit fares against each of the new regulation summary points listed and how the final Wylex star rating is achieved. Professional electricians should really help to guide the customer and offer the best and safest solution that their money can buy for today and for the future.

Wouldn't you agree that the more independent RCBO protected circuits that are used or maybe added to a consumer unit, the more an installation complies? The minimum customer's expectation will be set by the consumer unit you decide to install to set the overall star rating of the installation, which in turn sets the rating your customers will ultimately give you.

With the Wylex Solution 17 star rating system, professional electricians can easily select the most appropriate consumer unit and devices for each individual installation, from a basic minimum standard through to five star rating. Finally, like simply choosing a hotel room today, the Solution 17 star rating system will help installers to specify the most economically and electrically appropriate solution every time.. A wall chart, to remind you of what consumer units are available and their specifications, is available from Wylex, free of charge to any Voltimum user. To get your free 17th Edition wall chart use the form above.