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How big should a consumer unit be?

Arran Cameron

Alright, it's only a metal box. So is the bodyshell of a Mercedes Benz. It's what you put inside it that really matters. Is the biggest really the best, or is most of it just going to end up as dead space? In some countries domestic consumer unit are so large that you can almost walk inside them, whereas us Brits seem to be content with a puny little canister filled with just 4 or 5 MCBs or (heaven forbid) rewirable fuses.

Those mega sized consumer units aren't just for show. They are filled with all sorts of weird (to us backwards Brits) and wonderful (to local folk who can't live without them) control devices, alongside protection for wiring, semiconductors, humans, and curious pet cats. Yes, pet cats have sadly been killed by electrical fires and shocks resulting from outdated consumer units.

The consumer unit is the central control box for all the electrics in a house. How big should the box be in order to meet the requirements of today and tomorrow? Think - EV chargers, solar panels, more electric heating appliances, home automation etc. Do you recommend 2 (or more) row boxes over the single row boxes, which are the norm for British houses, if wall space permits?

Is there a recommendation for the layout of a 2 row box for a domestic installation? For example, should all MCB / RCBO be located on bottom row and other devices on the top row? Boxes with more than one row are currently used mainly for commercial buildings, or mansions, rather than average size houses.

Consumer units are relatively 'dumb' devices even if fitted with microprocessor controlled AFDD and timeswitches. There are few, if any, official components that offer the facility to remotely monitor a consumer unit or connect it to the IoT. This will potentially be the next stage of development of consumer unit technology. For example, the next generation of SPDs will report the times and the voltages of each transient, and make them available for remote monitoring. RCBOs will be remotely resettable as well as providing details of the time they tripped and the fault current - including that which flowed to earth via a curious cat.

Parents

  • Sizing is a very basic self question for qualified electricians. Period!

    Jaymack    

  • in reply to Jaymack

    But very basic questions don't always have simple answers.

  • in reply to Jaymack

    What does that mean?

  • in reply to Jaymack

    Electricians can fail to understand a customer's requirements both now and in the future. It's still commonplace for electricians to install a CU with provision for just 6 circuits assuming that's all a 'conventional' house requires.

    They often don't think about things like solar panels or home automation systems - or even outside lights.

  • in reply to Arran Cameron

    I wouldn't refer to such as "Electricians". It's a basic knowledge requirement. If such a person requires guidance then physical supervision is required.

    Jaymack

  • in reply to Arran Cameron
    Arran Cameron said:
    It's still commonplace for electricians to install a CU with provision for just 6 circuits assuming that's all a 'conventional' house requires.

    Upstairs and downstairs lights and sockets makes 4. Combi boiler so no need for immersion heater or showers. Gas cooker. Yep, that'll do!

  • in reply to Jaymack

    mmmm....I think this is a rather relevant question - I would like all DBs in the UK to have 50% more space inside. All 3 phase DBs have too little space in them down the sides - where the cables run - especially when installing a lot of RCBOs. I know the OP is primarily talking of domestic boards but three phase ones are used in domestic on occasion. Even single phase "domestic" DBs do require more space inside them (IMO) too. 

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  • in reply to Jaymack

    mmmm....I think this is a rather relevant question - I would like all DBs in the UK to have 50% more space inside. All 3 phase DBs have too little space in them down the sides - where the cables run - especially when installing a lot of RCBOs. I know the OP is primarily talking of domestic boards but three phase ones are used in domestic on occasion. Even single phase "domestic" DBs do require more space inside them (IMO) too. 

Children
  • in reply to tattyinengland

    Back to 1st principles.

    Simple answer, a dist board/consumer unit should be large enough to properly accommodate all of the required circuits!

  • in reply to tattyinengland

    How many spare spaces would you allocate for solar panels and an EV charger?

    Are there any other things that warrant spaces allocating for them?

  • in reply to Arran Cameron

    As many as the customer is prepared to pay for is the simple straight answer If you have the money and the space allows it, I'll stick you a 18/24/36 way 3phase board in if you wish. But be aware that with short product life cycles, you may not be able to fill that last couple of spare ways in 10 year's time because the manufacturer has discontinued the range.

    ." Electricians follow instructions and follow rules much more than carrying out problem solving and innovation that engineers do all the time."

    This is because these days they are not taught critical thinking and problem solving skills, but merely to slavishly follow 'the regs' without question

    If you wish to apportion blame, then look to the rulemakers and educators rather than the end product..

  • in reply to whjohnson
    whjohnson said:
    But be aware that with short product life cycles, you may not be able to fill that last couple of spare ways in 10 year's time because the manufacturer has discontinued the range.

    You make a valid point about manufacturers discontinuing products. It's more of an issue with protective devices than other accessories, which should generally be deemed as safe if they physically fit and can safely be connected. In Continental Europe it's common practice to use wire links in consumer units whereas the British practice is to use a rigid live busbar, although dual live neutral busbars are also common in Continental Europe. This possibly helps to explain why mixing protective devices from different manufacturers is more commonplace in Continental Europe than in Britain.

    whjohnson said:

    This is because these days they are not taught critical thinking and problem solving skills, but merely to slavishly follow 'the regs' without question

    If you wish to apportion blame, then look to the rulemakers and educators rather than the end product..

    I don't honestly think that engineering degrees are good at developing critical thinking and problem solving skills.

    I think the problem is the general nature of day to day work. Some jobs are better at fine honing critical thinking and problem solving skills than others.

  • in reply to whjohnson
    whjohnson said:
    But be aware that with short product life cycles, you may not be able to fill that last couple of spare ways in 10 year's time because the manufacturer has discontinued the range.

    Then instead of blanks, fit an appropriate MCB or RCBO. Everything is there in my garage ready for an EVCP, but the technology (and the Regs) were still in a state of flux at the time.

    We also have a big fat distribution circuit up into the attics, so that is PV sorted as well.

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