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 Yes, pet cats have sadly been killed by electrical fires and shocks resulting from outdated consumer units.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

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

  • in reply to Arran Cameron

    Do take care - I could say that in my experience as an experimental physicist specialising in solid state and electronics, some engineers are not so great either. We all have blind spots.

    !!!


    Mike

  • in reply to Arran Cameron

    Well, there might be a bit of "monkey see, monkey do". It's really a matter of talking to the customer. If the customer is a large landlord, economy may be at the forefront, but that's their decision.

    Isn't the real question, "what would I install for myself?"

    I rather like the Schneider "wireless" RCBO boards which I have seen at a NAPIT event, but £1k is enough to make anybody's eyes water. On the other hand, that might just be a quarter's electricity bill, so why the heck not?

  • in reply to Chris Pearson

    There's "monkey see, monkey do" in every profession...

    A few years ago there was a big debate on this forum about wiring up ceiling lights, and whether many electricians do it according to what they previously encountered or learned in training courses rather than considered different (and better) alternatives.

    Large landlords are one type of customer, but what I had in mind are small scale landlords who own just one or two houses, and more often than not just want things cheap and minimal with only the requirements of today and not tomorrow,

  • 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 Chris Pearson

    Fusebox do a nice double-stacker with all internal links and connectors pre-assembled for a good price.The Schneider items look to be something of an expensive faff, with lots of 'extras' to buy on top of what already is a very expensive board for what it is.

  • 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

    I see what you mean, but the size isn't the issue. Our current board is in fact two end-to-end.

  • 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.

Reply
  • 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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