Metering - Time running out for unmetered distribution
At the present time, orders for sub-distribution boards to be used in commercial 
premises only rarely include provision for metering, says Colin McAhren of Moeller Electric. He believes, however, that this situation is going to change dramatically in the very near future
It seems a very long time ago technical publications, including this very magazine, were full of articles announcing the introduction of Part L2 of the Building Regulations and explaining how this would lead to big changes in electrical distribution systems, particularly in relation to sub-metering. In fact, it was a long time ago: the year was 2006 and the final sections of Part L2 came into effect in October of that year.
Surely then, with a full two years gone by, compliance with the provisions of Part L2 has become routine? Unfortunately, it hasn't. In particular, Part L2, as we shall see in more detail later, contains provisions that mean almost all distribution boards used in commercial electrical installations should include sub-metering. But they don't.
How do I know? The answer is very simple. Moeller Electric is a major supplier of electrical distribution equipment and much of it is very clearly destined for non-domestic use. Not many Type B boards, for example, are used in the average home.
Surprisingly then, most of the orders we receive don't include any mention of sub-metering. In addition, we offer retrofit sub-metering solutions, and demand for these is also much lower than might reasonably be expected. Sub-metering is simply being neglected.
Before discussing why this is, let's rewind a little and refresh our memories as to why Part L2 was introduced and what it means in terms of electrical distribution systems. The first question is easily answered. Part L2 was introduced to help reduce energy consumption in commercial buildings, thereby protecting the environment and, incidentally, saving money for those that pay the energy bills for those buildings.
It seeks to achieve this by requiring property owners and tenants to have access to accurate and detailed information about their energy usage. An overall usage figure is not sufficient to meet this requirement; the information must be split between various types of energy usage.
In fact, Part L2 requires building occupiers to be able to account in detail for at least 90% of their energy usage for each type of fuel used, and that includes electricity. They must be able to say, for example, how much of the fuel is used for lighting, for heating, for air conditioning and so on.
The provisions apply to all new premises with floor areas of 500m2, and they also apply to existing premises when substantial modifications are made. This is usually interpreted as meaning modifications that need Building Regulations approval. In other words, they apply to almost all premises where new distribution boards are going to be fitted!
Now let's have a look at the implications for those distribution boards. As it is necessary to account for electricity usage separately for lighting, heating, etc., it's not hard to see that the overall metering installed by the electrical utility company is totally inadequate to meet the requirements of Part L2. What's needed is separate sub-metering for each type of load.
This is made even more clear in the regulations by explicit requirements for separate metering of certain load types. These include, for example, boiler installations rated 50 kW or more, chillers rated 20 kW or more and motor control centres feeding pump or fan loads with a total rating of 10 kW or more.
Perhaps the most important of these explicitly mentioned requirements, however, is final electricity distribution boards with loads totalling 50 kW or more. Most Type B boards exceed this figure when fully loaded, so Part L2 indicates strongly that feeds to almost all final distribution boards should be separately metered.
The upshot of what we've discussed so far is that distribution boards without sub-metering should be very much in the minority but, as we've already seen, exactly the opposite is true at the present time.
Why is this? That's not an easy question to answer, but the most probable explanation is that omitting the metering minimises the first cost of an installation, something which is always given a high priority by specifiers, even if the supposed economies lead to higher expenditure during the life of the building.
It must also be true that building inspectors are currently less than rigorous in their insistence on the provisions of Part L2 being met, possibly because they've seen so very few installations where sub-metering is correctly implemented.
Anyone, whether they're a contractor or a specifier, who is feeling a little complacent at this point about how easy it is to neglect Part L2 requirements should prepare themselves for something of a shock. Just when you thought it was safe to assume Part L2 was toothless, the rather sharper-toothed Energy Certificate for Buildings (ECB) has appeared on the scene!
From October 2008, it is a condition of selling or leasing commercial property that the landlord or vendor should supply an ECB. Rather like the ratings schemes for things like domestic freezers, ECBs give a rating for the energy performance of the building.
Buildings with poor energy ratings are likely to prove something of a liability, as would-be purchasers or tenants will have an all-too-clear indication that they'll be spending a lot of money on energy, and that they may well have to spend even more money somewhere down the road to improve the energy performance of their building.
But what has all this got to do with Part L2 of the Building Regulations in general, and with sub-metering in particular? The answer is that in buildings without proper sub-metering provisions, as prescribed by Part L2, it will be difficult, if not impossible to demonstrate good energy performance. It won't be at all surprising if the independent government-approved inspectors who issue ECBs take a very dim view of this, and give the building a poor energy rating.
So there it is - no sub-metering is likely to lead to a not-so-good ECB. And a not-so-good ECB will make a building hard to sell or let. It's not hard to see that the end result is going to be a big upsurge in interest in Part L2, and a big increase in demand for sub-metering, both for new and existing installations.
Let's now look at how this demand can best be satisfied. The most convenient place to provide sub-metering is undoubtedly at the distribution board. It is important, therefore, that any boards used should make provision for the fitting of meters.
In many cases this provision will be in the form of a meter box, and contractors in particular will need to give careful consideration to how easy this is to install, and whether it offers space for fitting any CTs that many need to be used in conjunction with the meters.
It's also important that the appearance of the meter box complements that of the rest of the distribution equipment - today's customers are unlikely to be happy with metering provisions that look like a bolt-on afterthought, even if that's exactly what they are.
One way to meet the need for monitoring energy usage separately for each type of load is to fit meters to all outgoing circuits. This is, however, an expensive and often inconvenient approach, particularly in simpler applications. In such cases, a better and more cost-effective solution is the use of split-load boards.
While usually having a single incomer, boards of this type group the outgoing circuits for lighting and power loads separately. This makes it easy to provide separate energy monitoring for each type of load with just two meters. Suitability for use in split-load configurations is, therefore, an important factor to consider when choosing distribution boards.
Some manufacturers, including Moeller Electric, have taken the growing need for sub-metering into account right from the earliest design stages of their latest distribution products. The result is complete ranges of products that make it easy to fit comprehensive metering, whether this is done during the assembly of the board, or as a retrofit operation on site.
Boards of this type have, for example, adequate room for the internal addition of CTs without them having to be crammed into inconvenient and inaccessible locations such as cableways.
The best products even allow meters to be added without the need for external meter boxes. With Moeller Electric's XEnergy modular distribution switchboards, for example, all that's needed is to replace the plain enclosure door with one that's fitted with a metering and display unit. This can be done easily, quickly and inexpensively either in the workshop or on site.
Unfortunately for the environment, and for occupiers of commercial buildings who are denied the information they need to optimise their energy usage, sub-metering in electrical distribution systems is currently the exception rather than the rule.
This regrettable situation must change, and it looks as if the introduction of ECBs is going to be the driving force to bring this change about. For contractors and specifiers, therefore, now is the time to dust off Part L2 of the Building Regulations and look at it again with renewed focus and interest!
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