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 Yes, pet cats have sadly been killed by electrical fires and shocks resulting from outdated consumer units.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

  • 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!

  • How big should a consumer unit be? 

    As big as is needed.... Slight smile

    Consumer Unit

  • I sometimes think French electrons are bigger than ours. And different rules about the height of the switches and mixing things in one enclosure. nice to see  a C16 on the  lights though - no tripping when the bulb fails. Still keeps it all together.


  • Another thing I have noticed in euro-boxes is that they don't mind at all if different brands of devices are mixed in the same board. I was looking at a Norwegian video where a 3 phase Hager board was filled with Hager main switches/fuseholders and RCDs but the mcbs were all ABB items.

    It seems the 'Thou shalt not mix brands' mantra doesn't apply in many parts of the continent. Must be a unique British protectionist hang-up which has become overly gold-plated as a supposed standard..

  • Actually  , something you may be able to help with (and sorry for taking this off topic!) Our main RCD (on the right of the image) will trip intermittently and we can't quite work out why. It will do it if we have too many things with a heating element on it such as if we have the water heater on and then switch on the kettle. Or if we have the Infrared heating panel on and then switch on the oven. There's no one thing that will do it although I did put on the kettle by itself once and that was enough to trip it. However, the kettle isn't a common factor as to when it trips. It just seems to be the catalyst to tip it over the edge. It's a 45 amp so should be enough to handle everything but it does trip annoyingly at really inconvenient moments! 

    I wonder if it's just a faulty main RCD or if there's something else going on? What would you suggest?