I'm contemplating a new CU.
To update from the current 60s(?) vintage fusewire thing. Are all MCBs/RCD/RCCB/RCBO's compatible, and 'plug and play' ?
Or is it more complex than that, with CUs varying in spacing, and only one brand will fit?
It's "more complex than that", *some* MCBs are interchangeable between different makes of CU but it's not a good idea to depend on it. I have fitted a few non-original MCBs in my CUs and the usual problem is with the busbar connections being incompatible but there other problems too.
Thanks.
Most are to DIN rail standard, but the devil is in the detail.
The fitting onto the rail is standard, but the terminal position may differ slightly. Since CUs have a stout copper bus bar normally, that can be a problem between different brands of MCB
The height and width of the forward projecting piece of the MCB, where it locates through the cutout in the front cover is standard. However, the amount forward by which they project can vary meaning that the cover might not close properly.
In short, it's a better idea to buy everything from one manufacturer.
Keep an eye open for packaged products. I don't particularly mean those that come with a whole load of MCBs because they will probably be the wrong mix. However, since an incoming breaker and an RCD are pretty much standard, there are packaged product deals with these already included at a better price than the sum of the parts.
I did have a stab at a thead on this a while ago - the intention being to gather together a list of interchangeable brands etc for a FAQ. The thread did not seem to get that for however. Such as it was can be found here:
FWIW you can add this to your database
New style Square D are the same as the New Merlin Gerin C60's
Square D KQ range can be converted to the above by removal of the busbar clip
Merlin C45's can be fitted with a busbar converter
Protec mcb's [ CEF own crapcious brand] fit Wylex NB range [doesn't affect us as we 'smuugly' have a load of NB and HB breakers in stock!!]>
NOTHING is compatible with old Square D
MEM Still make a compatible breaker for the Memera 2000 range [mid 1980, cream coloured, with a side hung door and a 'ribbed' front]
Nothing fits the older MEM smoke plastic fronted boards [mem still have old stock though]
If I think of any more I will post again
FWIW many years ago Wylex put out a installer alert regarding the CEF aftermarket mcbs. This related to a poor fit on the 'phase side' causing heat overload etc...be warned
If you're replacing the CU, what's the issue? Simply get everything from one maker. Different if trying to source replacements, I suppose.
I bought a Crabtree CU off Ebay (buy it now) with a choice of MCBs and more if needed at the same price. Excellent value. Could probably find the suppliers nick if interested.
Naah, thanks. There seems to be a seller sort-of-local to me, so maybe can lose the postage.
However, I really need to plan it properly, as part of a modest rewire. For example, I plan to be adding quite a few 2(or 1?)A round pin sockets, connected to a UPS. (for fishtank filters, emergency lighting) Then I need to work out if I want to be able to hook the generator up to the UPS, and how to distribute the low power 12V bus, ... (not to mention avoiding anything not obviously safe)
While trying to avoid feature creep like adding automatic load shedding to the UPS side, or the fact that with automatic load shedding triacs in there, it's not that much more work to make every socket controllably dimmable, ...
Fortunately, the wiring is relatively (1980) vintage PVC, so does not need wholesale replacement.
Right. But the same applies - just buy one you know you can get spares for. If you stick to the common brands like MK or Wylex any wholesaler should stock all the MCBs, etc.
None of that really effects the CU.
Is this a CU question?
I'd say that is the least of your worries given your plans.
Very true. In all but terms of space in the electricity cupboard - which I need to plan too.
This was a problem I could only solve by having more than one CU... None of the split load units were narrow enough to fit the avilable gaps.
That's possibly where I'll be going too. Though probably with an external generator/battery kennel.
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