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How big should a consumer unit be?

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 Yes, pet cats have sadly been killed by electrical fires and shocks resulting from outdated consumer units.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.

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


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

  • What does that mean?

  • 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.

  • 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.


  • 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!

  • 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. 

  • Back to 1st principles.

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

  • My experience, as an engineer, is that some electricians can get stuck in their ways. Electricians follow instructions and follow rules much more than carrying out problem solving and innovation that engineers do all the time.

    Electricians might think they know all there is to know about SPDs, but how many could develop such a device, or even determine that there is a good reason to have to develop such a device?!

    In my locality it's tricky to find tradesmen who are very good when it comes to owner occupied houses that don't burn a hole in your bank account, unless it's just the bare minimum the owner asks for. Instead, they overwhelmingly have a mindset geared to rentals, so tend to concentrate on offering the bare minimum. How many rentals have solar panels or EV chargers? How many that don't have them have a CU set up to accommodate them?

    So what do the electricians install as standard? A BG CU from Screwfix with provision for just 6 circuits, and no SPD unless the owner of the property specifically asks for one. If you want a 2 row box from Hager or Eaton installed, then expect to pay more than twice as much even if you supply all the parts and specify just 6 circuits at the outset with no fancy accessories, to have it installed by an electrician who is familiar with installing such devices. Most ordinary electricians will freak out at the sight of such consumer units, or ask a barrage of questions what you intend to put inside it, but more often than not take the advantage to charge more than twice as much as for the 6 circuit CU from Screwfix they usually install. If you want fancy accessories installed, then the electrician had probably never even seen such delights as a DIN rail mounted timeswitch before.

    As I stated in the OP, it's only a metal box.

  • Crikey that's dissed all electricians then. I'm guessing you've had a bad experience recently Arran Smirk

  • Crikey that's dissed all electricians then. I'm guessing you've had a bad experience recently Arran Smirk

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