How to choose the right consumer unit and what to put in it

August 21st 2018

Consumer units are often much more about what goes into them than what is already built in. Crabtree, one of Electrium’s leading brands in circuit protection, talks about choosing the right consumer unit and what to put in it.

When they say ‘the whole is greater than the sum of its parts’, they may not be talking about consumer units… but the analogy certainly fits!

A correctly selected and installed consumer unit plays a vital role in the safe use of electricity in the home. Its devices protect the installation and more importantly, the users, from faults and risks such as fire, and electrical shock.

Starbreaker consumer units have been designed to be easier, safer and faster to install, whether it’s a first-time installation, a re-fit or an upgrade, the range has been designed to be both backwards compatible as well as future-proofed.

Nothing demonstrates this better than the latest development in the circuit protection market.

New Regulations in the 18th Edition

With the release of the 18th Edition of the wiring regulations, which was published on 1st July 2018, a new type of circuit protection device was included under regulation 421.1.7 regarding AFDDs which stands for Arc Fault Detection Device. Starbreaker consumer units are the only consumer units that can accept AFDDs without the need for special busbars or assemblies, or on site adjustments.

Furthermore, because the busbar hasn’t changed since its launch AFDDs can be instantly fitted to any Starbreaker consumer unit, regardless of its age. 

Starbreaker consumer units use an innovative instant self connection system by employing a unique busbar system that devices simply plug into for instant push fit connections that give guaranteed factory quality connections.

This makes the installation of devices easier, safer and faster. AFDDs can be simply plugged into the fully insulated plug in busbar system for an easy installation that meet 18th Edition standards for additional protection against electrically ignited fires.

30mA RCD Protection Extended

Today’s typical domestic installation will have 30mA RCD protection on every circuit, especially as another new regulation in the 18th Edition (regulation 411.3.4) has extended the use of 30mA RCDs to include all lighting circuits in dwellings.

All of which means that each circuit in a consumer unit needs to have several types of protection against a variety of potential faults.

By combining Crabtree AFDDs (Arc Fault Detection Devices) with the new Miniature RCBO (Residual current Circuit Breaker with Overcurrent protection) Crabtree have created a single device, capable of providing protection against all the fault conditions as necessary.

This device includes MCB technology, RCD technology and AFDD technology, providing protection against overcurrent, short circuit, earth leakage and arc fault conditions, all in one DIN mounted plug in 2 pole device that also switches the neutral for even higher levels of safety. They also help designers and installers comply with the 18th Edition IET Wiring Regulations.

It’s important that installers understand that AFDDs detect the types of arc faults that cannot be detected by RCDs or MCBs. These new devices use digital technology to provide additional protection against fires caused by arcs in AC 230V final circuits.

The 30% Rule

To help to avoid unwanted tripping of RCDs from PE currents leaking through the protective conductor during normal (non fault) operating conditions the accumulated leakage current must be less than 30% of the RCD rating i.e. 30% of 30mA – see regulation 531.3.2.

Designers and installers will have to take account of PE currents when dividing the installation into the necessary number of circuits.

This is in addition to the requirements set out in Chapter 31 (314.1). Installing more individually protected RCBO circuits to supply fewer items of equipment will help to meet this requirement.

Only Use Manufacturer Approved Parts

Another new regulation, 536.4.203, refers to devices and components that are used in low voltage assemblies, such as consumer units, must only be those that have been declared suitable for that purpose by the manufacturer of the assembly.

Or put another way. Only use manufacturer approved parts, don’t mix brands of devices, or control items.  Using unapproved parts will invalidate manufacturer guarantees and may result in an unsafe installation.

Meter Tails

The 18th Edition also includes regulation 522.8.5 which requires every cable to be installed in a way that avoids any mechanical strain and makes sure that there is no strain on the conductors and connections.

Consumer unit meter tails are included in this requirement. This is in addition to any other requirements to provide protection to tails at the point of entry into metal consumer unit enclosures etc.

Health and Safety

Regulation 462.1.201 requires a means of isolation (a main linked switch or circuit breaker) at the origin of every installation and in situations where this will be operated by ordinary persons, e.g. on a consumer unit in a domestic household, the main switch must interrupt both live conductors (L and N) of a single phase supply. 

Starbreaker Mini RCBOs and AFDDs provide this same safety protocol to individual circuits too because they include switched neutral as standard.

Periodic Inspections

The 18th Edition recommends periodic testing and inspection (regulation 135.1).

Testing can be a time consuming and costly activity, but Starbreaker Miniature RCBOs allow IR testing to be carried out without disconnecting and reconnecting circuit cables because they include two pole isolation as standard. Just switch off and test. Easier, safer, faster.

So, whether it’s a brand new installation, an addition or upgrade, Crabtrees’ Starbreaker consumer units and devices (Miniature RCBOs and AFDDs) can be simply plugged into the fully insulated plug self-connecting busbar system.

Providing an easy installation that now includes additional protection against electrically ignited fires.

Get more on the 18th Edition

Be clued up on the 18th Edition and the changes that are coming through by visiting our 18th Edition Area.

We'll be talking more about AFDDs, Surge Protection, RCD and more.

Check out our 18th Edition area here.

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