Views taken from the top of the BT Tower Birmingham


  1. BulletNow consider your electric cooker consumes a maximum of 12kW - exactly as in the previous example. On face value, it seems that we will have to go for the expensive 10 mm cable at £2.50 per metre length!

  2. However, because this is a cooker, the 17th Edition wiring regulations actually tell us that we can take into account the concept of ‘diversity’ in our circuit design process. We take the first 10 amperes of required current and thirty percent of the ‘full load’ that remains, which gives a total current of 22 amperes. And the cost of cabling is back to 49 pence per metre length. But if you do want a 13A socket outlet built into your ‘cooker box’ then you will have to go for 4 mm cable!

  3. There are also other factors to take into account such as the ‘voltage drop’ that may occur and are dependent on circuit length.

  4. BulletAs a final example - say that you have at your electricity in-coming supply board one of those  ‘consumer’ units that ‘trips’ out if there is a fault with one of your appliances that cause a ‘leakage  current’ of more than 30 mA. But there is no regular pattern to the tripping and neither can you determine a faulty appliance.

  5. The problem is often ‘solved’ by swapping part of your consumer unit for a tripping device that requires a higher tripping current!

  6. There are several problems with this approach including that it may directly contravene the 17th Edition wiring regulations (Regulations 411.3.3, 411.5, 522.6.7, 522.6.8, 701) and that whilst you are also waiting for your faulty appliances to finally reveal themselves as they gradually deteriorate, someone might be electrocuted during the interval!

  7. The scenario that has been described is one where there is more than one appliance with a ‘faulty’ leakage current. Individually, the faulty appliances will not cause tripping and your electricity supply will not be disconnected. But the sum of the individual fault leakage currents will!

  8. In such circumstances we have no doubt that we would be able to locate any faulty appliances and tell you what has been happening and exactly how much current each appliance has been ‘leaking’!

For all customers!

What equipment and suppliers do we use?

It is a requirement of the 17th Edition wiring regulations (BS7671:2008) that:

  1. Regulation 133.1.1

  2. ‘Every item of equipment shall comply with the appropriate British Standard. In the absence of an appropriate British Standard, reference shall be made to the appropriate IEC standard or the appropriate national standard of another country’

This is why there has been a requirement for all electricians to hold a City & Guilds qualification in BS7671:2008 by January 2010, so that your installation will be carried out as it should be with your safety in mind:

  1. Regulation 120.1

  2. ‘This Standard contains the rules for the design and erection of electrical installations so as to provide for safety and proper functioning for the intended use’

We select equipment manufactured by, but not exclusively, such companies as Crabtree, Wylex, MK and Volex. If there is a specific manufacturer that you would like us to use on your behalf then all you have to do is let us know

Also, if you would like to select your own specific fittings, such as down lighters for example, then we can fit them for you and there can be no ‘hidden charges’ on the purchasing of such equipment because you have purchased it!


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Typically for the homeowner!

  1. BulletConsider that you would like 4 electrical heaters to be installed in your downstairs rooms and each of the heaters has a 3kW capacity. Calculation confirms a current requirement of over 52 amperes.

  2. The 17th Edition wiring regulations confirm the minimum cable size must be 10 mm and the cost of such cable is over £2.50 per metre length.

  3. But let us suggest two circuits each of which connects to 2 heaters. Each circuit now carries half of the originally calculated current and in accordance with the 17th Edition wiring regulations the minimal cable size for each circuit must now be 2.5 mm - and the cost of such cable is 49 pence per metre! And if you draw out the circuits you will see that you will not actually require twice the amount of cable!

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