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 Yes, pet cats have sadly been killed by electrical fires and shocks resulting from outdated consumer units.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

  • Our main RCD (on the right of the image) will trip intermittently and we can't quite work out why.

    Is it a simple RCD? I was under the impression that the first tier of RCD in France was typically EdF's device which is a combined 500mA RCD and load limiter, so unlike an ordinary RCD is prone to tripping on prolonged overload. I'd guess it'll have a thermal element in it rather like MCBs so will tend to be driven by the average load over a reasonable length of time rather than the exact load at the moment of tripping.

       - Andy.

    edited to add:

    https://uk.rs-online.com/web/p/mcbs/4820987

    "Two-pole low voltage subscriber circuit breakers (for French blue tariff).

    :
    Rating can be adjusted to limit the power on the EDF contract taken out."
  • in reply to AJJewsbury

    The one you see in the image Andy is just the secondary one. We also have one at the meter which is at the top of the driveway. A secondary one was fitted alongside the main board just to stop me having to walk all the way up to the top of the driveway in order to reset it if that one trips. This one will trip before the one at the meter does but as I say, we get a lot of nuisance tripping with it. 

    Wondering if we should just take it out and I leave a pair of hiking boots by the door instead Joy. #justbeinglazy 

  • in reply to Lisa Miles

    First step - can you get us a pic of the writing on the one that trips, and also of the one at the end of the drive, that does now, then we know if it is an RCD or an RCBO or something more complex with a maximum load -limit function. Then we can give you more informed unhelpful advice... And even if there is no simple answer it is good to know why.
    Mike.

  • in reply to mapj1

    Thanks Mike, I'll have to get back to you on this though as I'm back in the UK at the moment so not able to take a pic! Slight smile

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  • in reply to mapj1

    Thanks Mike, I'll have to get back to you on this though as I'm back in the UK at the moment so not able to take a pic! Slight smile

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