In addition to the basic power and lighting circuits that include central heating and immersion heaters, it is becoming increasingly common to include extra circuits for external lighting, power showers, bell transformers, staircase lighting and accessories with their own protective devices in the consumer unit. This proliferation of circuits makes the consumer unit a hub for domestic energy management which can produce significant energy savings when allied with DIN rail modular devices such as analogue or digital timers.
The emphasis is on greater flexibility and increased protection, irrespective of whether the unit is factory built or of the self-assembly type. Protective devices such as mcbs, residual current devices (rcd) and residual current circuit breakers with overcurrent protection (rcbo) bring higher levels of safety and allow consumer units to be tailored to individual requirements.
Unfortunately, instead of being given the due consideration at the design stage that these protective components deserve, they are often fitted as an afterthought. Electrical contractors can best serve their clients' interests by providing higher capacity consumer units to facilitate new circuits at some future time. This would make a new loft or rear extension a far less disruptive process electrically than it otherwise might be. Furthermore, a consumer unit fitted with, say, spare mcb ways for future external lighting or an immersion heater, leaves the safety of the installation in the hands of the original electrical contractor; it avoids the possibility of other operatives installing non-compliant protective devices at some future date.
The past few decades have seen manufacturers develop bigger, more flexible consumer units to suit changing lifestyles, installation practice and wiring regulations. It used to be considered good practice to install just two circuits in a dwelling – one upstairs and one downstairs. Today, the host of appliances in a typical kitchen has necessitated the introduction of separate kitchen circuits in many installations. Indeed, so elaborate has the situation become that a typical domestic arrangement will today comprise separate circuits for ground and first floor lighting (both 6 A or 10 A), ground and first floor power (both 32 A), cooker (40 A), immersion heater (16 A), external power (16 A) and one or possibly two spare ways in the consumer unit to allow future circuits.
Catering for this profusion of circuits has resulted in today's modular consumer units having as many as 12 outgoing ways, in addition to any control and automation devices that may be fitted to an accessory DIN rail. But having accepted that maintaining as many spare outgoing ways as possible is a desirable option, which circuit breakers do you install given the alarming proliferation of mcbs with similar profiles?
This is one of the problems associated with European harmonisation, which has seen the arrival of a plethora of mcbs from different manufacturers. It is therefore easy to install a non-dedicated mcb into another manufacturer's consumer unit, with the result that the installation does not comply with the 16th Edition Wiring Regulations. This is because each company tests its own circuit protection devices with its own consumer units and so can issue the appropriate test certificate without which an installation will be non-compliant.
This has implications for both suppliers and installers. In some circumstances where the non-dedicated mcb profile differs from that produced by the consumer unit manufacturer, some installers trim the mcb to achieve the necessary fit. However, this can result in overheating and the creation of a potentially hazardous situation, particularly where the non-dedicated mcb has screws with a reduced contact area.
Various consumer units are 'de-engineered' to save on costs and may result in inferior products. Alternative materials may be used giving the perception that a product has not been 're-engineered' to maximise on features but cost reduced offering ease of construction not installation. It is generally accepted that the most robust and well-made consumer units have a metal back-plate and incorporate a fixed, full, solid copper busbar with solid copper links. However, it should be added that flexible links are an advantage when using a modular plug-in busbar system.
Many of the pitfalls so far discussed can be avoided by careful consideration of the consumer unit to be installed. Selection should be on the basis that the unit in question is allied with a range of control modules with which it has been tested by the manufacturer. Using a different manufacturer's product may not have the appropriate test certificate and may therefore constitute a non-compliant installation.
The modern consumer unit has a significant role to play in the safe, effective and energy conscious management of domestic electricity. When making their selection, contractors should give due consideration to their clients' current and future needs, rather than being influenced by short-term cost considerations. This will not only benefit all concerned, but will ensure that installations are as safe and as flexible as they can be.
A climate without change
Imagine it: no change in the climate, ever. No hotter or colder weather. The light is always the same. There’s no rain, but it’s never too dry. It sounds like heaven – or hell depending on your outlook on life. Well, don’t fret, there’s no chance of the British weather becoming that dull, and that is why the Institute of Arable Crop Research (IACR) has a controlled environment facility at the Rothamstead Experimental Station. The facility has 23 walk-in rooms, 43 cabinets, 12 daylit rooms, and 29 insect rearing rooms. An in-house team has installed Hager’s TP&N and SP&N boards in an expansion programme at the facility. The boards provide circuit protection and controlled switching of lighting, ventilation, heating and air conditioning as well as controlling the moisture and CO2 levels. Crop research is a long drawn out process and the climate in the labs has to be constant for the entire time. The staff at the centre have developed a bespoke control system called Environcon. Sensors monitor the local climate and the information is fed into Environcon which switches the motorised vents, blinds, pumps, heating or air conditioning via the contactors and relays. This keeps the environment perfect for growing crops and experimenting with insecticides and fertilisers. It must be nice, though, at the end of the day, to come out into the pouring rain and buffeting wind. Then again, maybe not.what’s new in circuit protection
Bill Switchgear Bill Switchgear introduces the Talisman Multi 1, a modern mccb panelboard system offering flexibility in the choice of incoming and outgoing mccbs. It is ideal for the subdistribution of three-phase supplies at each floor or load centre in large premises. Wylex Wylex has launched a new family of consumer units called the NH range. Units use insulated enclosures and have mains switch, rcd and split-load configurations. Moeller Electric’s Moeller Electric’s PKZM0 fuseless motor protection circuit breakers combine the function of isolation, motor switching, short-circuit and overload protection in a single unit. This enables motor starters to be assembled from a circuit breaker and a contactor. F&G Installations F&G Installations is now able to supply its Concept 2000 consumer units with a high level of built-in intelligence. The inclusion of a control relay adds an array of timing and switching functions that are suitable for controlling lighting, heating and ventilation. Merlin Gerin offers a greater choice of circuit breaker and protection modules. This allows a wider range of applications to be covered by standard panels that can be produced faster than bespoke items.Crabtree
Source
Electrical and Mechanical Contractor
Postscript
Darren Garbett is product manager, domestic circuit protection, Wylex.
